The safety of child wheelchair occupants in road passenger vehicles

The safety of child wheelchair occupants in road passenger vehicles
The safety of child wheelchair occupants in
road passenger vehicles
TRL Report
TRL667
The study comprised a number of elements leading to a dynamic sled test programme with
instrumented child dummies. The research found that children in wheelchairs do not receive a level
of protection that is comparable to that for children in child restraints or vehicle seats. Changes
in legislation are therefore required to address and hence improve their protection. There are
three key influences: the vehicle, the restraint system and the wheelchair. All three areas must be
addressed for improvements in protection to be made, and for the greatest improvements, vehicle,
restraint system and wheelchair manufacturers must work together.
Related publications
TRL559
Review of the road safety of disabled children and adults. K Williams, T Savill and A Wheeler. 2002
PPR076
Development of measures for improving child protection in minibuses, buses and coaches.
G J L Lawrence and W M S Donaldson. 2006
CT22.4
Transport for the elderly and disabled update (2004-2007)
CT111.2
Taxi and paratransit update (2001-2005)
TRF8
The safety of wheelchair occupants in road passenger vehicles. M Le Claire, C Visvikis, C Oakley, T Savill
and M Edwards. 2003
The safety of child wheelchair occupants in road passenger vehicles
This TRL Report presents the findings of a study carried out by TRL for the UK Department for
Transport (DfT). The aim of the study was to examine the safety of children in wheelchairs in road
passenger vehicles. The key question was whether children who remain seated in their wheelchairs
are afforded a level of protection that is comparable to that for children travelling in a vehicle based
restraint system.
The safety of child wheelchair
occupants in road passenger
vehicles
C Visvikis, M Le Claire, O Goodacre,
A Thompson and J Carroll
Price code: T
ISSN 0968-4107
Published by
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United Kingdom
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United Kingdom
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TRL667
TRL
24/06/2008 11:08:41
The safety of child wheelchair occupants in road
passenger vehicles
C Visvikis, M Le Claire, O Goodacre, A Thompson and J Carroll
TRL Report TRL667
TRL Report TRL667
First published 2008
ISBN 978-1-84608-722-6
Copyright Transport Research Laboratory 2008
This report has been produced by TRL, under/as part of a
Contract placed by the Department for Transport (DfT), and
should not be referred to in any other document or publication
without the permission of the DfT. The views expressed
are those of the authors and not necessarily those of the DfT.
Published by IHS for TRL
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Nine Mile Ride
Wokingham
Berkshire RG40 3GA
United Kingdom
Tel: +44 (0) 1344 773131
Fax: +44 (0) 1344 770356
Email: [email protected]
www.trl.co.uk
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or
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United Kingdom
Tel: +44 (0) 1344 328038
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Email: [email protected]
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waste and promoting recycling and re-use. In support of these
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Contents
Abstract
vi
Glossary of terms
vii
Executive summary
ix
1 Introduction
1
1.1 Existing regulatory framework
1.1.1 Wheelchair restraint in vehicles
1.1.2 Child restraint in vehicles
1.1.3 Project aim
1.1.4 Scope
2 Overview
2
2
4
5
6
7
2.1 Literature and information review
2.1.1 Approach
2.1.2 Summary
2.2 Field study
2.2.1 Approach
2.2.2 Vehicles
2.2.3 Wheelchair types
2.3 Impact protection
2.3.1 Approach
2.3.2 Vehicles
2.3.3 Crash test pulses
2.3.4 Wheelchair types
2.3.5 Anthropometric dummy selection
2.3.6 Injury criteria
2.3.7 Impact test equipment
2.4 Non-impact protection
2.4.1 Background
2.4.2 Approach
2.4.3 Vehicles
2.4.4 Driving conditions
2.4.5 Wheelchair types
3 M1 and M2 forward facing
7
7
7
8
8
9
10
11
11
12
12
14
21
24
25
25
25
26
26
26
26
27
3.1 Field study
27
i
3.2 Scope of testing
3.3 Test design – phase 1
3.3.1 Key issues
3.3.2 Final test selection
3.3.3 Test matrix
3.3.4 Test set up
3.4 Findings – phase 1
3.4.1 Relative safety of current situation
3.4.2 Effect of restraint geometry
3.4.3 Effect of wheelchair stiffness
3.4.4 Effect of head and back restraint
3.4.5 Anchorage loading
3.4.6 Occupant space requirements
3.5 Test design – phase 2
3.5.1 Key issues
3.5.2 Final test selection
3.5.3 Test matrix
3.5.4 Test set up
3.6 Findings – phase 2
3.6.1 Effect of restraint geometry
3.7 Conclusions
4 M1 and M2 rear facing
28
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30
35
41
43
45
45
46
51
53
58
58
59
60
61
62
62
63
63
67
70
4.1 Field study
4.2 Scope of testing
4.3 Test design
4.3.1 Key issues
4.3.2 Final test selection
4.3.3 Test matrix
4.3.4 Test set up
4.4 Findings
4.4.1 Relative safety of current situation
4.4.2 Effect of wheelchair stiffness
4.4.3 Effect of head and back restraint
4.5 Conclusions
70
71
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76
81
82
84
84
84
86
90
5 M3 forward facing
91
5.1 Field study
5.2 Approach
5.3 Conclusions
91
92
92
6 M3 rear facing
94
ii
6.1 Field study
6.2 Approach
6.3 Conclusions
94
96
97
7 M3 non-impact protection
99
7.1 Scope
7.2 Testing methodology
7.3 Results
7.3.1 Observations before testing
7.3.2 Wheelchair space fitted with stanchion
7.3.3 Wheelchair space fitted with horizontal retractable rail
7.4 Discussion
7.5 Conclusions
8 Cost analysis
99
101
104
104
106
107
108
111
113
8.1 Introduction
8.2 Child wheelchair users and their involvement in collisions
8.3 M1 vehicles (cars and taxis)
8.3.1 Vehicle design changes
8.3.2 Annual production estimates
8.3.3 Cost estimates
8.4 M2 vehicles (minibuses)
8.4.1 Vehicle design changes
8.4.2 Annual production estimates
8.4.3 Cost estimates
8.5 M3 vehicles (buses and coaches)
8.5.1 Vehicle design changes
8.5.2 Annual production estimates
8.5.3 Cost estimates
8.6 Wheelchairs
8.6.1 Wheelchair design changes and indicative cost
estimates
8.7 Comparison of benefits and costs
8.8 Summary
9 Discussion
113
114
118
118
118
118
119
119
119
119
119
119
120
120
120
120
124
126
127
9.1 General observations
9.2 Wheelchair restraint system
9.2.1 Forward facing wheelchairs
9.2.2 Rear facing wheelchairs
9.3 Occupant restraint system
iii
127
128
128
128
129
9.3.1 Forward facing wheelchairs
9.3.2 Rear facing wheelchairs
9.4 Head and back restraint
9.4.1 Forward facing wheelchairs
9.4.2 Rear facing wheelchairs
9.5 Wheelchair design and stiffness
9.5.1 Forward facing wheelchairs
9.5.2 Rear facing wheelchairs
9.6 Limitations of the project
129
130
130
130
131
132
132
132
132
10 Conclusions
134
11 Recommendations
136
11.1 M1 and M2 forward facing
11.1.1 Vehicle anchorages
11.1.2 Occupant restraint
11.1.3 Head and back restraint
11.1.4 Occupant space
11.1.5 Wheelchair design and stiffness
11.2 M1 and M2 rear facing
11.2.1 Vehicle anchorages
11.2.2 Occupant restraint
11.2.3 Head and back restraint
11.2.4 Occupant space
11.2.5 Wheelchair design and stiffness
11.3 M3 forward facing
11.3.1 Vehicle anchorages
11.3.2 Occupant restraint
11.3.3 Head and back restraint
11.3.4 Occupant space
11.4 M3 rear facing
11.4.1 Head- and backrest
11.4.2 Restricting wheelchair movement into the gangway
136
136
137
138
138
139
140
140
140
140
141
141
141
141
142
143
143
143
143
144
Acknowledgements
145
References
146
Bibliography
148
Appendix A.
Literature and information review
iv
149
A.1 Introduction
A.2 Legislation and policy background
A.2.1 All children
A.2.2 Children in wheelchairs
A.3 Biomechanics of children
A.3.1 All children
A.3.2 Children in wheelchairs
A.4 Current practices
A.4.1 Introduction
A.4.2 M1 vehicles
A.4.3 M2 vehicles
A.4.4 M3 vehicles
A.5 Performance of children’s wheelchairs and restraint systems
A.5.1 Accident studies
A.5.2 Laboratory tests and simulations
A.6 Discussion
A.7 Conclusions
A.8 Recommendations
A.9 References
Appendix B.
B.1
B.2
B.3
B.4
B.5
B.6
B.7
B.8
C.1
C.2
C.3
C.4
Field study of vehicle and wheelchair interaction 177
Introduction
M1 and M2 forward facing
M1 and M2 rear facing
M3 forward facing
M3 rear facing
Conclusions
Recommendations
References
Appendix C.
177
179
184
188
190
192
193
193
Injury criteria and associated performance limits 194
Hybrid III three year old dummy
Hybrid III six year old dummy
Hybrid III ten year old dummy
References
Appendix D.
149
149
149
152
155
155
158
160
160
160
161
163
163
163
166
168
170
171
171
Test results
194
195
196
196
197
D.1 M1 and M2 forward facing test results
D.2 M1 and M2 rear facing test results
v
198
200
Abstract
This report presents the findings of a study carried out by TRL for the UK
Department for Transport (DfT). The aim of the study was to examine
the safety of children in wheelchairs in road passenger vehicles. The
key question was whether children who remain seated in their
wheelchairs are afforded a level of protection that is comparable to that
for children travelling in a vehicle based restraint system.
The study comprised a number of elements leading to a dynamic sled
test programme with instrumented child dummies. The research found
that children in wheelchairs do not receive a level of protection that is
comparable to that for children in child restraints or vehicle seats.
Changes in legislation are therefore required to address and hence
improve their protection. There are three key influences: the vehicle, the
restraint system and the wheelchair. All three areas must be addressed
for improvements in protection to be made, and for the greatest
improvements, vehicle, restraint system and wheelchair manufacturers
must work together.
vi
Glossary of terms
AIS
Abbreviated Injury Scale
ANSI
American National Standards Institute
CCIS
Cooperative Crash Injury Study
CHILD
CHild Injury Led Design
COST
Cooperation in the field of scientific and technical
research
DHSS
Department of Health and Social Security
DfT
Department for Transport
EC
European Commission
ECWVTA
European Commission Whole Vehicle Type Approval
EuroNCAP
European New Car Assessment Programme
FMVSS
Federal Motor Vehicle Safety Standard
HIC
Head Injury Criterion
ISF
TRL’s Impact Sled Facility
ISO
International Organisation for Standardisation
M1 vehicles
Vehicles with ≤ 8 seats in addition to the driver’s seat
M2 vehicles
Vehicles with > 8 seats in addition to the driver’s seat
and a maximum mass ≤ 5 tonnes
M3 vehicles
Vehicles with > 8 seats in addition to the driver’s seat
and a maximum mass > 5 tonnes
MADYMO
Proprietary ‘multi-body’ numerical modelling code
MHRA
Medicines and Healthcare products Regulatory Agency
vii
NEISS
National Electronic Injury Surveillance System
NHTSA
National Highway Traffic Safety Administration
NPACS
New Programme for the Assessment of Child restraint
Systems
OPCS
Office of Population Census and Surveys
PMHS
Post Mortem Human Subject
RESNA
Rehabilitation Engineering and Assistive Technology
Society of North America
SI
Statutory Instrument
SAE
Society of Automotive Engineers
TRL
Transport Research Laboratory
UNECE
United Nations Economic Commission for Europe
viii
Executive summary
The safety of children who remain seated in their wheelchairs when they
travel raises a number of issues. The UK Department for Transport
(DfT) commissioned TRL to investigate these issues for children
travelling in road passenger vehicles involved in front impact collisions.
The DfT also wished to examine the stability of children’s wheelchairs
within the protected space in buses during normal driving manoeuvres.
The study compared the level of protection afforded to children seated in
their wheelchair with that afforded to children travelling in a vehicle
based restraint system. The aim was to develop the knowledge needed
to inform policy decisions on appropriate requirements for M1, M2 and
M3 vehicles (i.e. private vehicles, taxis, minibuses, coaches and urban
buses).
The study began by reviewing published literature and existing
legislation and standards. This review was supplemented with
information gained from organisations involved in the transport of
children. A field study was then carried out to examine the way children
and their wheelchairs interact with real vehicles and restraint systems.
The final stage was to carry out physical observations and sled testing;
firstly, looking at wheelchair displacement in low floor buses during
normal driving conditions; secondly, comparing the level of impact
protection provided for children in wheelchairs with that provided for
children in vehicle based restraint systems.
For the purposes of the research, the vehicles were grouped as follows:
•
M1 and M2 vehicles with forward facing wheelchair passengers.
•
M1 and M2 vehicles with rear facing wheelchair passengers.
•
M3 vehicles with forward facing wheelchair passengers.
•
M3 vehicles with rear facing wheelchair passengers.
M category vehicles are defined in the European Commission Directive
2007/46/EC (Annex 2). Previous research carried out by TRL for the
DfT using adult dummies demonstrated that there is a lower risk of injury
in M3 vehicles compared with M1 and M2 vehicles. While it would have
been desirable to examine all vehicle categories in the impact test
ix
programme, it was necessary to prioritise M1 and M2 vehicles. This
allowed thorough investigation of M1 and M2 vehicles with a more
comprehensive range of children’s wheelchairs. Recommendations
were made for M3 vehicles, but these were based on observations of the
vehicles and on the test results for M1 and M2 vehicles.
The study found that children in wheelchairs do not receive a level of
protection that is comparable to that for children in child restraints or
vehicle seats. Changes in legislation are therefore required to address
and hence improve protection. There are three key influences: the
vehicle, the restraint system and the wheelchair. All three areas must be
addressed for improvements in protection to be made, and for the
greatest improvements, vehicle, restraint system and wheelchair
manufacturers must work together.
The vehicle must provide sufficient space to reduce the risk of the child’s
head striking the interior during a collision. A head and back restraint
must be provided for children in wheelchairs, irrespective of the direction
they face in a particular vehicle. This is the only means of ensuring that
the head and neck of a child in a wheelchair are afforded a comparable
level of protection as the head and neck of a child in a vehicle based
restraint system. It is essential that children in wheelchairs are provided
with at least a three point seat belt. The best practice is to anchor the
diagonal part of a three point belt to the vehicle above the shoulder level.
The seat belt should distribute the restraint forces over the strongest
parts of a child’s anatomy. It is critical that wheelchairs do not interfere
with or obstruct the path of the belt. Wheelchairs must be capable of
withstanding the forces in a collision of appropriate severity, if they are
intended to be used in a vehicle. The dynamic test conditions in United
Nations Economic Commission for Europe (UNECE) Regulation 44 are
appropriate to examine the performance of safety equipment in M1 and
M2 vehicles.
x
1 Introduction
Access for disabled people is an important aspect of the Department for
Transport’s (DfT) strategy and vision for the future of transport. Disabled
people should have the same access to transport as non-disabled
people and they should be provided with a comparable level of
protection during driving manoeuvres and in the event of a crash.
Access to transport can determine whether a person can live
independently, find a job, attend education, see friends and family and
take part in leisure activities. It can mean the difference between social
inclusion and exclusion within a community and can therefore have a
strong impact on an individual’s quality of life.
More than ten years ago, the Disability Discrimination Act 1995 was
passed into UK law. The Act is intended to end discrimination against
disabled people and allows the Government to make regulations in this
respect. Accessibility regulations have since been introduced for rail
vehicles and public service vehicles, and measures for taxis are
currently being considered.
These provisions will ensure that both vehicles used for personal use
and public transport will be accessible to wheelchair users who wish to
remain seated in their wheelchairs when they travel. In previous
research for the DfT, TRL investigated the safety of travelling in a
wheelchair in a range of M category vehicles (see Section 2.2.2). This
work helped to establish the relative level of safety afforded to
wheelchair seated adults compared with passengers travelling in vehicle
seats.
The number of children using wheelchairs in the UK has now risen
above 100,000 (www.wheelchairchildren.org.uk). In many cases, when
travelling in a vehicle, younger children can be transferred to a
conventional child restraint system; however, this becomes more difficult
as they grow older. As a result, parents and children report that their
access to services, social activities, education and employment broaden
or narrow depending on the accessibility of transport (Audit Commission,
2003). Since disabled children are also protected from discrimination
under the Act, the DfT needs to ensure that they are provided with an
appropriate level of safety compared with children restrained by
conventional means.
A great deal of research has been carried out on the protection of
children in child restraint systems, but the relative safety of children
1
using wheelchairs is less clear. Children are not simply small adults;
they are proportioned differently, their key organs are in different places
and their tissues have different biomechanical properties. Measures
introduced to improve access and safety for wheelchair seated adults
must also be compatible with children using wheelchairs and crucially,
they must not increase the risk of injury.
1.1
Existing regulatory framework
1.1.1 Wheelchair restraint in vehicles
In the past, people who wished to remain seated in their wheelchair
during transit were excluded from most forms of public transport. There
were no boarding aids to get on and off the vehicle and no space for the
wheelchair inside. Since that time, regulations passed under Part 5 of
the Disability Discrimination Act 1995 have led to growing numbers of
new accessible vehicles coming into service on Britain’s roads and
railways. This section outlines the way in which the 1995 Act deals with
transport and how wheelchair users are affected. It also describes the
changes introduced by the Disability Discrimination Act 2005 and its
supporting regulations. Finally, having established the legislative
framework for the vehicle, it sets out the requirements for the
wheelchair, in accordance with the Consumer Protection Act 1987.
Technical requirements for some M category vehicles are covered by
the Public Service Vehicles Accessibility Regulations 2000 (SI 2000 No.
1970; as amended). The Regulations benefit transport industries by
providing clear dimensions and other requirements (such as the need for
restraints) for different vehicles. They benefit disabled people by
ensuring vehicles used for public transport have adequate provision for
them and by setting ‘end dates’ by which all vehicles must comply.
Since the end of 2000, all new buses that carry more than 22
passengers on local and scheduled services have had to meet these
Regulations. This is achieved by providing a protected space for a
wheelchair user who, in most buses, faces rearwards against a padded
backrest. Coaches on local and scheduled services have to meet the
same regulations as buses. New coaches that carry more than 22
passengers have had to meet general accessibility requirements since
the end of 2000. However, unlike buses, the wheelchair accessibility
requirements for coaches were deferred until January 2005. All coaches
within the scope of the Regulations must be compliant with both the
general and wheelchair accessibility requirements by 2020. The
wheelchair faces forwards in a coach and must be restrained by a tiedown system and the occupant must be provided with a seat belt.
2
The Government recognises the vital role that taxis play in the
transportation of disabled people, and is committed to bringing forward
requirements for taxis. Consideration is currently being given as to how
this might be achieved, and this will comprise evaluation of all the
options, including both regulatory and non-regulatory approaches. All
licensed taxis in London have had to be wheelchair accessible since
January 2000 and some local authorities will only give new licences to
taxis that can carry wheelchairs. In London taxis (traditional ‘black
cabs’), wheelchair users face rearwards against the bulkhead that
separates the driver and passenger compartments. The wheelchair is
restrained with a tie-down system, adequate to prevent the wheelchair
from moving during the rebound phase of a crash. A seat belt is also
provided for wheelchair seated passengers. Elsewhere, London taxis
are sometimes used, but adapted people carriers or van based vehicles
are also allowed. In some of these vehicles, the wheelchair user will
travel facing forwards with a wheelchair and occupant restraint system in
place.
Part 5 of the Disability Discrimination Act 1995 provided the framework
for very specific technical regulations to be introduced. However,
disabled people could still be refused entry to an accessible vehicle
because transport vehicles were excluded from Part 3 of the Act. This is
the part of the Act that deals with access to goods, facilities, services
and premises. When the Act was passed in 1995, Parliament
introduced the exemption because there were very few accessible public
transport vehicles, especially for wheelchair users. The Disability
Discrimination Act 2005 enabled the Government to pass regulations to
lift the exemption for certain vehicles. The Disability Discrimination
(Transport Vehicles) Regulations 2005 (SI 2005 No. 3190) were made
under this power and came into force on 4th December 2006. As a
result, it is unlawful for public transport operators to discriminate against
disabled people or to offer a service at a lower standard or on different
terms to a disabled person because of their disability. For the first time,
transport providers will have to take positive steps to make their services
in respect of transport vehicles accessible to disabled people (Disability
Rights Commission, 2005).
Wheelchairs themselves are subject to the Consumer Protection Act
1987. This gave Ministers the power to make the Medical Device
Regulations 2002. As part of their CE marking process (which indicates
that one or more of the procedures referred to in the Regulations have
been followed), manufacturers of wheelchairs must undertake a risk
analysis. For the transportation elements of their risk management,
many wheelchair and seating manufacturers look towards the ISO
3
Standards for wheelchair transportation safety to show they have
reduced the risks and met some of the essential requirements of the
Regulations (Lynch, 2003).
1.1.2 Child restraint in vehicles
Seat belts provide a high level of protection for adults as they are
designed for people 150 cm (about 5 ft) and taller. Smaller occupants
cannot achieve the correct placement and fit (of the adult belt) over the
shoulders and pelvis and for some children, such as infants, it is
necessary to apply the restraint force over altogether different areas of
the body. For these reasons, a dedicated child restraint system must be
used to accommodate the needs of a child in a vehicle. However,
children in public transport vehicles are likely to be restrained only by a
seat belt. This is because their restraint use tends to be driven by the
minimum legal requirement. Part of the challenge for public transport
vehicles is the difficulty of having a supply of suitable child restraints on
hand. The following section outlines the way in which the Road Traffic
Act 1988 affects children. It covers the technical requirements for seat
belts in vehicles and describes the law on restraining children (and the
Government’s proposals to change the law). Finally, it sets out the
safety standards for child restraints sold in the UK and explains how
these standards are applied.
The Road Vehicles (Construction and Use) Regulations 1986 (SI 1986
No. 1078; as amended) were made under the Road Traffic Act. These
Regulations set out the minimum legal requirements for seat belts in
motor vehicles. In fact, most vehicles on the road today are likely to
have seat belts fitted; however, the application of the law depends on
the type of vehicle and the year of manufacture. For instance, seat belts
have been mandatory in the front seats of all new cars since 1965 and in
rear seats since 1987. Before 1987, child restraints were attached to the
car by means of straps bolted to the floor and parcel shelf. This gave a
stable installation, but relied on parents to take the time and effort to
modify their cars and fit the devices and led to many older children
travelling unrestrained. Since then, child restraints have been attached
to the car with seat belts. Although this is a simple and universal
method of attaching the child restraint, the original function of seat belts
was to restrain adult occupants. Some aspects of the belt assembly
design such as the anchorage locations, buckle size and length of the
belt can be in conflict with the need to secure child restraints.
The 1986 Regulations did not require seat belts to be fitted in the rear of
minibuses and coaches. However, the Regulations were amended in
4
1996 (SI 1996 No. 163), which set requirements for minibuses and
coaches to be fitted with seat belts, when used in certain circumstances.
The new Regulations stated that children (aged three to 15 years) on
organised trips must be provided with a seat belt and a forward facing
seat. Both the complete assembly and the belt anchorages were
required to meet the relevant European Standards.
Further Construction and Use Regulations were made in 2001 (SI 2001
No. 1043), to extend mandatory fitting requirements to minibuses and
coaches (except those designed for urban use with standing
passengers). As a result, three point seat belts have to be installed in all
forward facing seats in new minibuses. In coaches, two point belts are
permitted, provided that an appropriate energy absorbing seat is present
in front.
Although many vehicles now have seat belts fitted, the law does not
always require passengers to use them, and in the case of children, the
law does not always require the most appropriate form of restraint to be
used. The Motor Vehicles (Wearing of Seat Belts) Regulations 1993 (SI
1993 No. 176; as amended) set out the law on using seat belts and child
restraints. The law says that children must use an appropriate child
restraint when travelling in a car (except in a taxi when a child restraint is
not available). The law also says that any passenger aged three years
and over must wear a seat belt (if one is installed) in a minibus or coach.
From May 2008, where the Regulations call for the use of a child
restraint, it must meet the requirements of United Nations Economic
Commission for Europe (UNECE) Regulation 44.03 (or subsequent
versions). In fact, all child restraints sold in the UK must conform to the
Regulation, which includes a front impact test and a rear impact test,
although the rear impact test is required for rear facing devices only.
Side impact is not currently part of the Regulation; however, a side
impact test procedure for child restraints has been developed as part of
a consumer assessment and rating scheme for child restraints called
NPACS (New Programme for the Assessment of Child restraint
Systems).
1.1.3 Project aim
The DfT wished to examine the safety of children in wheelchairs in
vehicles. The project objectives were to develop the knowledge about
the effects on the safety of child wheelchair occupants travelling in road
passenger vehicles and inform policy decisions on appropriate
requirements for M1, M2 and M3 vehicles.
5
1.1.4 Scope
The project investigated the issues for children travelling in M category
vehicles involved in front impact collisions. The key question for the
project was whether children who remain seated in their wheelchair are
afforded a level of protection comparable to that for children travelling in
a vehicle based restraint system. The project focused on children aged
from three to ten years inclusive. Infants and very young children were
considered more likely to transfer to a child restraint system than travel
in a wheelchair. Older children are comparable in size to small adults;
hence their protection was addressed in the previous DfT project.
6
2 Overview
2.1
Literature and information review
2.1.1 Approach
A literature review was necessary to establish the relevance of any
previous research that had been carried out. The review comprised
published research from the UK and abroad and any other information
that it was possible to obtain.
TRL recognised that a review of this nature would highlight what was
known about the safety of children in wheelchairs from a science and
engineering point of view. It would also highlight any gaps in the
knowledge that should be addressed in the project. However, TRL was
concerned that the requirements of end users – children, parents and
transport operators – may not be found in the literature in any depth. To
give a feel for these practical issues, the literature review was extended
to gather relevant information and experiences from other organisations.
The literature and information review can be found in Appendix A, but a
summary is provided in the following section.
2.1.2 Summary
The literature review was divided into four sections. The first section of
the review examined the legislative and policy background relevant to
the carriage of children in vehicles, including children in wheelchairs.
This revealed that legislation is in place (or coming into force) that
covers the type and specification of wheelchair tie-down and occupant
restraint systems in certain vehicles. However, the technical
requirements for the performance of the restraint system (including the
wheelchair) do not address the protection of children directly in the way
that UNECE Regulation 44 does. It was also noted that there is no
legislation in place governing the use of a restraint system by children in
wheelchairs.
The second section of the literature review examined the biomechanics
of children. This highlighted the significant amount of research in child
biomechanics that can be drawn on by designers of child restraint
systems. This has led to solutions in restraint design that are tailored to
the child’s level of growth and development. The performance of these
solutions in real accidents confirms that children can withstand the
7
forces in a collision when they are restrained appropriately and
according to their level of development. No relevant literature could be
found on the biomechanical characteristics of children that use
wheelchairs. Nevertheless, it seems likely that some of the same
principles for restraint design would apply.
Another section of the literature review examined current practices in the
restraint of children in wheelchairs in M category vehicles. This was
based on discussions with organisations involved in the carriage of
children in wheelchairs and also on observations made of wheelchair
transportation at a special school. It was not intended to be a scientific
study, but instead provided a useful insight into some of the issues. This
revealed that parents and carers of children in wheelchairs would
appreciate any advice on the most appropriate way to restrain their
children including when it is safe for them to travel while seated in their
wheelchair. It would also appear that there is a wide variation in the
quality of the vehicles and equipment used to transport children in
wheelchairs. Transport operators would benefit, therefore, from further
guidance on the ideal vehicle and restraint system specifications for the
carriage and restraint of children in wheelchairs. Their drivers and
escorts would benefit from further guidance on the need for and use of
this equipment.
The final section of the literature review examined research carried out
to investigate the performance of children’s wheelchairs and restraint
systems during collisions. Unfortunately, there was no information about
their performance in real accidents. It is possible that very few accidents
have occurred involving children seated in their wheelchair in a vehicle;
however, it is also the case that accident databases are not usually
detailed enough to record whether an occupant was seated in a
wheelchair. Although some laboratory studies were identified in the
review, these were relatively few in number and tended to focus on
manual wheelchairs with a dummy that represented a six year old child.
2.2
Field study
2.2.1 Approach
The field study investigated the way children and their wheelchairs
interact with real vehicles and restraint systems. A range of
representative wheelchairs and vehicles was used to identify potential
problems in the orientation of the wheelchair, the location of vehicle
structures and the geometry of the (wheelchair and occupant) restraint
system. In each case, a dummy was seated in the wheelchair and
8
restrained in a vehicle using whatever means were provided or
recommended by the manufacturer. A qualitative assessment was then
made of the potential problems within the vehicle environment or with
the restraint system. A selection of the worst or most common problems
that were identified in each vehicle fed directly into the test programme
for further investigation.
2.2.2 Vehicles
The project considered the safety of wheelchair occupants when
travelling in M category vehicles which are defined according to the
European Commission Directive 2007/46/EC (Annex 2). M category
motor vehicles with at least four wheels used for the carriage of
passengers are categorised as follows:
•
M1: ≤ 8 seats in addition to the driver’s seat.
•
M2: > 8 seats in addition to the driver’s seat and a maximum mass ≤
5 tonnes.
•
M3: > 8 seats in addition to the driver’s seat and a maximum mass
> 5 tonnes.
A number of different M category vehicles were examined for the field
study. These were grouped as follows:
•
M1 and M2 vehicles with forward facing wheelchair passengers.
These included both converted small multi-purpose vehicles and
minibuses.
•
M1 and M2 vehicles with rear facing wheelchair passengers. In
fact, no M2 vehicles were found in which a wheelchair user regularly
travels rear facing. The vehicles examined were all M1 vehicles that
were purpose built or specially adapted to function as a taxi.
•
M3 vehicles with forward facing wheelchair passengers. These
were coaches.
•
M3 vehicles with rear facing wheelchair passengers. These were
buses used on scheduled urban services.
For each group, a number of different vehicles were examined to ensure
that the findings were not influenced by a particular example.
9
2.2.3 Wheelchair types
Four wheelchairs were used during the field study. The wheelchairs
were selected to represent the many different devices that children use.
The four wheelchairs were:
•
A folding manual wheelchair with a sling canvas seat.
•
A rigid manual wheelchair for active users.
•
An electric wheelchair with a reclining or tilting function.
•
A buggy style wheelchair with a seat comprising a postural
positioning system.
All four wheelchairs were production models loaned to TRL by the
manufacturers. The manual wheelchair, electric wheelchair and buggy
were suitable for use in a vehicle as stated in the product literature. The
active user wheelchair was not suitable for use in a vehicle; however,
this type of wheelchair is popular with some children and may be used in
transport despite the manufacturer’s instructions. The wheelchairs are
shown in Figure 1.
Basic manual wheelchair
Active wheelchair
10
Electric wheelchair
Buggy style wheelchair
Figure 1 Wheelchairs used in the field study
It was understood that these wheelchairs represented a limited cross
section of the devices available for children. However, for the purposes
of the field study, they included a number of key features shared by the
many different designs that are found. It was concluded, therefore, that
the selection of wheelchairs covered the widest range of features
considered to be important for the investigation of wheelchair interaction
with vehicles.
2.3
Impact protection
2.3.1 Approach
The impact test programme was carried out in two phases. The first
phase was intended to identify any problems in the way children in
wheelchairs travel in vehicles and compare their level of protection with
that for children in vehicle based restraint systems.
After the first phase was completed, the results were analysed to
determine where children in wheelchairs received lower levels of
protection. The aim was to propose solutions that could increase the
level of protection afforded to children in wheelchairs in line with children
in vehicle based restraints. It was anticipated that these solutions could
be encouraged through recommendations for vehicle legislation;
however, it became apparent that wheelchair design may also need to
11
be addressed. The second phase of testing was carried out to evaluate
possible solutions, where necessary.
2.3.2 Vehicles
Impact protection was examined for children travelling forward or rear
facing in M category motor vehicles. M category vehicles are defined in
the European Commission Directive 2007/46/EC (Annex 2) and in
Section 2.2.2 of this report. For the purposes of the project, the vehicles
were grouped as follows:
•
M1 and M2 vehicles with forward facing wheelchair passengers.
•
M1 and M2 vehicles with rear facing wheelchair passengers.
•
M3 vehicles with forward facing wheelchair passengers.
•
M3 vehicles with rear facing wheelchair passengers.
Previous research with adult dummies demonstrated that there is a
lower risk of injury in M3 vehicles compared with M1 and M2 vehicles
(Le Claire et al., 2003). While it would have been desirable to examine
all vehicle categories in this test programme, it was necessary to
prioritise M1 and M2 vehicles. This allowed thorough investigation of M1
and M2 vehicles with a more comprehensive range of children’s
wheelchairs. Recommendations were made for M3 vehicles, but these
were based on observations of the vehicles and on the test results for
M1 and M2 vehicles.
2.3.3 Crash test pulses
Le Claire et al. (2003) highlighted that the dynamic test conditions in
UNECE Regulation 44 (Child Restraint Systems) were appropriate to
represent a collision in an M1 or an M2 vehicle. The UNECE Regulation
44 test conditions were therefore used in the test programme to examine
the level of protection afforded to children in wheelchairs.
It is important to note that the conditions for the dynamic test in UNECE
Regulation 44 differ from those in the ISO Standards for wheelchair
safety in transport (ISO 7176-19:2001 and ISO 10542-1:2001). The
differences are summarised in Figure 2.
UNECE Regulation 44 prescribes separate limits for deceleration and
acceleration sleds. For example, the impact speed, deceleration curve
and stopping distance of the sled are required for deceleration devices.
12
The impact speed is the speed of the sled immediately before the impact
when no external forces are in action. The sled deceleration curve must
fall within an upper and lower limit, which form a corridor. Although the
limits are relatively wide, it is impossible to achieve a deceleration curve
that follows either limit of the corridor with an impact speed of
50 +0-2 km/h and a stopping distance of 650 ± 50 mm. In the case of
acceleration devices, the total velocity change and deceleration curve
are required. The same corridor is used; however, there is an additional
requirement (for acceleration devices) which states that the curve must
rise above a defined line within the corridor. This line is also illustrated
in Figure 2.
The ISO Standards do not prescribe separate limits for deceleration and
acceleration devices. Instead, there are limits for the velocity change
and deceleration curve irrespective of the type of sled. The overall
velocity change is usually determined by integration of the curve and can
incorporate the rebound phase of an impact when a deceleration sled is
used. The upper limit that is applied to the sled deceleration or
acceleration curve is similar to that in UNECE Regulation 44; however, it
does not limit the gradient of the curve during the onset. The lower limit
does not form a fixed corridor. Instead, the curve must exceed certain
levels of deceleration for the periods of time indicated in Figure 2.
30
UNECE Regulation 44
Deceleration devices
Test speed: 50 +0-2 km/h
Stopping distance: 650 ± 50 mm
Acceleration devices
Velocity change: 52 +0-2 km/h
25
a(t) > 20 g for 15 ms
Deceleration (g)
20
ISO Standards
+2
Velocity change: 48 -0 km/h
a(t) > 15 g for 40 ms
15
10
5
(tf - t0) > 75 ms
0
0
20
40
60
80
100
120
140
Time (ms)
Figure 2 Comparison of UNECE Regulation 44 test conditions with ISO
Standards
The key difference in the test conditions is the use of impact speed or
increased velocity change (for acceleration sleds) in UNECE
13
Regulation 44 and velocity change (irrespective of the sled type) in the
ISO Standards. For instance, an impact speed of 50 km/h results in a
total velocity change in excess of 50 km/h due to the contribution of the
rebound speed. While the velocity change in the ISO Standards is
48 +2-0 km/h, kinetic energy increases as a function of the square of the
velocity. Hence this moderate difference can influence the severity of
the test quite markedly.
This is illustrated further by Figure 3, which compares the mean sled
deceleration in a sample of five UNECE Regulation 44 tests with a
sample of five ISO tests. The higher impact speed and consequently
velocity change in the UNECE Regulation 44 tests resulted in higher
levels of sled deceleration than the ISO tests. Furthermore, the higher
levels of deceleration were maintained for a longer period, which
included the phase of the impact when the occupant was in contact with
the restraint system.
30
25
UNECE Regulation 44
ISO Standards
Deceleration (g)
20
15
10
5
0
0
20
40
60
80
100
120
140
Time (ms)
Figure 3 Comparison of UNECE Regulation 44 deceleration curves with
ISO Standards
2.3.4 Wheelchair types
TRL examined the wheelchair market to gain an understanding of the
different wheelchairs that children use. The aim was to highlight the key
aspects of their design that could affect their performance in a vehicle
collision. The outcome of this approach was a selection of wheelchairs
to use in the test programme.
14
There are various ways of classifying the different types of wheelchairs
on the market. For the purposes of this project, the following categories
were used:
•
Buggies.
•
Manual wheelchairs.
•
Electric wheelchairs.
Some children are provided with a supportive seating system for comfort
and posture. These commercial or custom made seating systems fit on
the top of a buggy or wheelchair chassis. However, it is sometimes the
case that the seating system has a different manufacturer than the base
or wheelchair with which it is being used. Seating systems are common
in the children’s wheelchair market and were therefore included as an
additional category for investigation in the project.
The remainder of this section looks at the different wheelchairs within
each category and introduces the wheelchairs selected for the impact
test programme.
Buggies
There are many different buggy models on the market; however, two
distinct styles have emerged. Throughout this report, these will be
referred to as basic buggies and supportive buggies. Basic buggies
have a reinforced nylon or fabric seat without additional support for the
child. The key features to examine when children are travelling in a
vehicle are:
•
The seat is forward facing and can have an adjustable backrest
angle.
•
The backrest may be tall enough to support the child’s head.
•
A harness is usually fitted for management of posture.
•
The push handles are large on some models and extend rearwards
of the buggy.
Supportive buggies are fitted with various support pads that help to keep
the child in a stable position. The key features to examine when children
are travelling in a vehicle are:
15
•
The seat is usually forward facing, but some rear facing and some
interchangeable models are available.
•
Postural supports can be fitted near to the child’s head, upper body,
hips and legs.
•
The seat and backrest tend to be rigid to allow the postural supports
to be attached securely.
•
The backrest may incorporate a headrest.
•
A harness is usually fitted for management of posture.
•
The backrest is usually adjustable for angle and some models allow
the seat and backrest to be fixed while they are tilted rearwards.
•
The push handles are large on some models and extend rearwards
of the buggy.
TRL used both basic and supportive buggies in the test programme.
These are shown in Figure 4 and Figure 5 respectively. The devices
were production models and were suitable for use forward facing in a
vehicle, as stated in the product literature.
Figure 4 Basic buggy
Figure 5 Supportive buggy
16
Manual wheelchairs
There are various terms in use to describe manual wheelchairs.
However, in this report, manual wheelchairs are referred to as basic
wheelchairs or active user wheelchairs. With the use of the wheelchair
in a vehicle in mind, this approach took account of the key differences
found between certain models.
Basic wheelchairs are the archetypal or classic wheelchairs familiar to
most people. They can be self propelling or attendant propelled. The
key features to consider when children are travelling in a vehicle are:
•
The backrest is high enough to stabilise the lower thoracic region.
•
The backrest is usually upright, but some models can be fitted with
a reclining backrest. In comfort wheelchairs, the seat and backrest
can be fixed while they are tilted rearwards.
•
A headrest can be fitted as an accessory.
•
Side guards are fitted to the wheelchair to protect the user’s clothes
from splashes from the wheels.
•
Push handles are usually fitted, even in the case of self propelling
models.
Active user wheelchairs are lighter than basic wheelchairs and can be
more adjustable. The key features to consider when children are
travelling in a vehicle are:
•
The backrest is relatively low compared with other wheelchair types.
•
A headrest is unlikely to be fitted.
•
Side guards are fitted to the wheelchair to protect the user’s clothes
from splashes from the wheels.
•
Push handles are not usually fitted.
TRL used basic and active user wheelchairs in the test programme. The
basic wheelchair is shown in Figure 6. A reclining version was also used
and is shown in Figure 7. The active user wheelchair is shown in Figure
8.
17
The basic manual wheelchairs were both suitable for use in a vehicle
forward facing, as stated in the product literature. The active user
wheelchair was not suitable for use in a vehicle; however, it was
included in the test programme to examine whether it would be possible
to develop some means of allowing these wheelchair users to travel
while seated in their wheelchairs.
Figure 7 Reclining basic manual
wheelchair
Figure 6 Basic manual wheelchair
Figure 8 Active user manual wheelchair
18
Electric wheelchairs
Although there is a wide range of electric wheelchairs available for
children, the most common devices are fairly typical in design. The key
features to consider when children are travelling in a vehicle are:
•
They are powered by rechargeable batteries that are usually
positioned at the rear of the wheelchair chassis. This can result in a
gap between the rear of the backrest and the rear of the chassis.
•
A headrest can be fitted as an accessory.
•
The backrest is usually adjustable for angle and some models allow
the seat and backrest to be fixed while they are tilted rearwards.
TRL used an electric wheelchair in the test programme. This is shown in
Figure 9.
Figure 9 Electric wheelchair
Supportive seating systems
Supportive seating systems help children to achieve a functional seating
position. Some systems are modular, while others are permanently
moulded to an individual. Modular seating systems are built up from a
19
number of adjustable components. The key features to consider when
children are travelling in a vehicle are:
•
Postural supports can be fitted near to the child’s head, upper body,
hips and legs.
•
A headrest is likely to be fitted to the seating unit.
•
A harness is usually fitted to assist posture.
•
Many systems aim to achieve a stable, upright, seated position;
however, some children are provided with a tilt-in-space unit. These
allow the seat and backrest to remain fixed while they are tilted
rearwards.
Moulded seating systems are unique to each user’s anatomy. The key
features to consider when children are travelling in a vehicle are:
•
The moulded seat follows the contours of the body very closely.
•
A harness is also fitted to assist posture.
Two modular seating systems were used in the test programme; one
was used with an upright base, while the other was used with a tilt-inspace base. These are shown in Figure 10 and Figure 11 respectively.
A moulded seating system was not used in the project. A child in a
moulded seat would not be accommodated easily by a standard
wheelchair tie-down and occupant restraint system. Furthermore,
current test dummies would not permit a full investigation of the
situation. Although a seat could be moulded to a crash test dummy, it
could not reproduce the physical characteristics and issues associated
with certain medical conditions.
20
Figure 11 Supportive seating
system with a tilt-in-space base
Figure 10 Supportive seating
system with an upright base
2.3.5 Anthropometric dummy selection
TRL considered three types of child dummies for the impact test
programme: the P Series, the Q Series and the Hybrid III Series. Each
dummy approximates the weight and size of children at the age they are
intended to represent. There are, however, differences in their geometry
and material properties such that dummies representing the same age
can display markedly different behaviour in dynamic tests. This is
because part of the challenge of designing a child dummy is the lack of
biomechanical data for children. In an attempt to address this, the
biomechanical response requirements for adult dummies are scaled to
give corresponding requirements for children. Unfortunately, the
techniques used and the assumptions made can influence the dummy
requirements.
For these reasons, the P, Q and Hybrid III Series of child dummies differ
greatly, both in terms of their degree of biofidelity and also their
measurement capacity. The P Series was developed in the late 1970s
alongside UNECE Regulation 44, which came into force in 1982. The
Regulation describes a full range of dummies representing children from
birth to ten years. The P Series has subsequently been adopted by the
European New Car Assessment Programme (EuroNCAP) and a great
21
deal of experience has been gained in the use and capabilities of this
dummy. The advantage of the P Series is its low cost and robustness
for routine testing of restraint systems; however, it is not biofidelic and
has very limited measurement options. Instrumentation is fitted in the
head, chest and in some cases the neck, but the head acceleration is
known to be unreliable and is not part of the Regulation. Although there
are no injury criteria for the dummy, limits are applied to the head
excursion and chest acceleration in Regulation 44.
The Q Series was developed as a potential successor to the P Series. It
represents a significant improvement in terms of its measurement
capacity; however, a number of issues remain to be resolved before the
dummy can be considered as a replacement for the P Series in
regulation. Research carried out by TRL showed that the behaviour of
the Q Series in dynamic tests is different to the P Series. However, no
comment can be made on the biofidelity of the Q Series, because it is
yet to be agreed and published. Although its measurement capacity is
an advantage, there are no injury criteria or regulatory limits that can be
used with this dummy. Progress towards injury risk curves was started
by the European Commission CHILD project, but the curves were not
developed fully within the project and the work is ongoing.
The Hybrid III Series was developed in the USA by the Society of
Automotive Engineers’ Biomechanics Committee and the National
Highway Transportation Safety Administration (NHTSA). The dummy
has been adopted by the Federal Code in the USA (49 CFR Part 572
Subparts N and P) and is mandated for use in testing child restraint
systems to meet Federal Motor Vehicle Safety Standard No. 213
(FMVSS 213). The dummy has demonstrated robustness in private
wheelchair tests carried out by TRL and has the capacity for greater
measurement than the P Series. The main advantage of the Hybrid III
Series, however, is the availability of regulatory performance limits from
FMVSS 213 and additional published injury criteria in the literature.
Table 1 summarises the differences between the three dummies. TRL
selected the Hybrid III Series for the project because it represents the
best option in terms of measurement capacity and injury criteria.
22
Scaled injury criteria
available and some
regulatory limits
Medium
None
High
None, but has
regulatory limits for
chest acceleration
Low
Injury criteria
Cost of use, calibration
and damage
All body regions
3 years to 10 years
All body regions
Full range from birth Birth to 6 years
to 10 years
Availability
Used by TRL in
private wheelchair
testing without
damage
Chest acceleration.
Head unrealistic
except in P1.5
Not established for
this type of testing
Significant damage
unlikely
Robustness
Hybrid III Series
Measurement capacity
Q Series
P Series
Table 1 Comparison of child dummies
23
2.3.6 Injury criteria
The performance limits for the dynamic test in FMVSS 213 apply to the
Head Injury Criterion (HIC) and resultant chest acceleration recorded
with the Hybrid III Series. However, additional injury criteria have been
proposed in the literature for these and other body regions of the dummy
(Eppinger et al., 2000; Mertz et al., 2003).
Injury criteria and their associated limits can be a useful means of
interpreting dummy measurements. They are usually derived from Post
Mortem Human Subject (PMHS) tests occasionally supplemented with
volunteer tests. Animal tests and accident reconstructions are also
techniques that are used, but much less frequently. The standard
method is to replicate the human tests with the dummy and then
compare the dummy measurements with the presence or absence of
injury. Statistical methods are used to create injury risk curves, from
which the injury limits are taken to represent a percentage risk of injury.
The PMHS samples available for such research tend to be elderly
adults. There are a number of ethical considerations that have limited
the use of PMHS children to a few tests, while the use of children in
volunteer testing is impossible. For these reasons, there are few data
available from which to develop injury risk functions and subsequent
limits for child dummies. However, this is sometimes resolved by scaling
injury limits for adults to take into account the differences in mass, size
and stiffness between adults and children.
Eppinger et al. (2000) presented a set of injury criteria and limits for
several dummies including the Hybrid III three year old and the Hybrid III
six year old. The Hybrid III ten year old had not been developed at that
time. Mertz et al. (2003) presented a set of updated injury limits for the
Hybrid III three and six year old dummies and also provided limits for the
ten year old dummy. Some of the limits presented by Mertz et al. (2003)
differed slightly from Eppinger et al. (2000), possibly because different
assumptions were made during the scaling process or because the
values were chosen to represent a slightly different risk level.
Exceeding an injury limit does not necessarily imply that a child would
experience the associated injury. It is usually the case that the limit
values are chosen to represent a relatively low risk of injury, typically a
5 percent risk of Abbreviated Injury Scale (AIS) ≥ 3 injury. Furthermore,
the relationship between injury and the corresponding injury criteria and
scaled limit is not well established for children. It is essential, therefore,
24
to take a pragmatic approach when applying the injury criteria and limits
to child dummy measurements.
A summary of the injury criteria and associated performance limits is
given in Appendix C.
2.3.7 Impact test equipment
The Impact Sled Facility (ISF) at TRL was used for the test programme.
The ISF comprises a rail mounted sled which is accelerated by elastic
cords and decelerated by polyurethane deceleration tubes and olives.
Dummy measurements were recorded by a DTS data acquisition
system. The data were analysed using the frequency response classes
described in SAE J211 (2003).
Two high speed digital cameras (500 fps) were used to record each
impact test. One camera was positioned perpendicular to the sled to
show the dummy at the point of impact and during its subsequent
motion. Another camera was positioned to observe lap belt penetration
in the forward facing tests or interactions with the bulkhead in the rear
facing tests.
2.4
Non-impact protection
2.4.1 Background
The Public Service Vehicles Accessibility Regulations 2000 (SI 2000 No.
1970; as amended) allow a wheelchair user on an urban bus to travel
rear facing in a protected area, against a back restraint or bulkhead.
The Regulations also demand a method for restricting lateral movement
of the wheelchair into the gangway, such as a vertical stanchion.
Previous research carried out for the DfT by TRL examined the extent of
such movement during normal driving conditions (Le Claire et al., 2003).
A dummy was seated in a wheelchair, while a bus was driven through a
manoeuvre that generated levels of lateral acceleration similar to those
recorded on real bus routes. Wheelchair displacement was observed,
but it was restricted by the vertical stanchion on the edge of the
wheelchair space. Children’s wheelchairs are narrower than those for
adults and some have pushchair style handles. It was necessary to
examine, therefore, whether the back restraint or methods for restricting
lateral movement described in the Regulations are adequate for
children’s wheelchairs.
25
2.4.2 Approach
A child dummy was seated in a wheelchair in the wheelchair space of a
low floor bus. The vehicle was then driven through a manoeuvre that
generated up to 0.4 g of lateral acceleration. Similar acceleration levels
were recorded in real journeys by Stone (1999; unpublished Project
Report).
Different sized dummies and different wheelchair types were used to
examine whether the key features of the wheelchair space in current
vehicles are appropriate for children. The study methodology and
findings are presented in detail in Section 7.
2.4.3 Vehicles
Two low floor vehicles were used for the study; one was fitted with a
vertical stanchion, the other with a retractable rail.
2.4.4 Driving conditions
The vehicle was driven in a semicircle with a radius of 20 metres, at a
speed of 21 - 23 miles per hour.
2.4.5 Wheelchair types
The wheelchairs used for these experiments were those used in the field
study. These are shown in Section 2.2.3 in Figure 1.
26
3 M1 and M2 forward facing
3.1
Field study
The field study included several M1 and M2 vehicles in which a
passenger in a wheelchair travels forward facing. In each vehicle,
dummies representing children aged three, six and ten years old were
seated and restrained in a range of wheelchairs. An overview of the
methods was given in Section 2.2 and the results of the study are
described in detail in Appendix B.
The study highlighted three main areas of concern: the geometry of the
occupant restraint system, the protection of the child’s head behind the
wheelchair and finally the amount of clear space around the child. In
previous research with adult dummies, the location of the diagonal belt
anchorage was an important factor in the performance of both the
wheelchair and the restraint system (Le Claire et al., 2003). Dynamic
sled tests demonstrated the benefit of an upper anchorage point
compared with a floor mounted anchorage. While the location of the
diagonal belt anchorage was also important for children, the field study
revealed that the path of the lap belt was the critical aspect of the
restraint geometry.
The geometry of the lap belt was influenced by the location of the
anchorages in the vehicle, but also by the design of the wheelchair. In
M1 vehicles with a permanent wheelchair space, the lap belt anchorages
were relatively wide to allow access to the space from the rear and to
accommodate a range of wheelchairs and occupants. However, this
tended to reduce the contact area between the lap belt and the dummy’s
pelvis, which might have affected its performance in a collision. In M1
and M2 vehicles with a flexible wheelchair space, the lap belt
anchorages and consequently the seat belt buckle were attached to floor
tracking behind the wheelchair. As a result, it was sometimes the case
that the diagonal part of the seat belt passed around the ribs of the
dummy before joining the lap belt at the buckle. The wheelchair
influenced the geometry of the lap belt by obstructing its path. These
obstructions were caused by side guards fitted to the wheelchair to
protect the user’s clothes from wheel splash and by hip support pads
fitted to the wheelchair to meet the user’s postural needs.
None of the vehicles examined provided a head and back restraint for
the wheelchair user. Furthermore, in the smaller vehicles the rear of the
dummy’s head was in close proximity to the vehicle structure or boarding
27
aid. In a collision, a child would have been at risk of neck injury through
overextension or of head injury through contact with the vehicle.
The amount of space in front of the wheelchair user was also important,
but varied significantly between vehicles. In one of the smallest
vehicles, the space was limited and the legs of the dummy were
adjacent to rigid parts of a folded seat. It was possible that the head of a
child in a similar position may also have been able to contact these parts
in a collision.
3.2
Scope of testing
The aim of the test programme was to examine whether children in
wheelchairs and children in vehicle seats or child restraints are likely to
receive a comparable level of protection in a collision. When children
travel forward facing, their protection is influenced by their wheelchair,
the vehicle they are travelling in and also by the restraint system.
When it is used in transport, a wheelchair takes the place of a vehicle
seat. It must, therefore, be able to withstand the forces in a crash
without transferring excessive forces to the child, to the same extent as
a vehicle seat. This is partially explored by the dynamic test in ISO
7176-19:2001; however, the Standard does not address occupant
loading. Since children use a range of different wheelchairs, as
highlighted in Section 2.3.4, it follows that the type of wheelchair could
influence their risk of injury in a collision. Furthermore, each wheelchair
type has various features and adjustments that could also affect the risk
of injury. With these points in mind, it was considered important for the
project to include all types of wheelchairs in common use by children. It
was also considered important to investigate the effect of the features
and adjustments that were most relevant for transport.
Assuming that the vehicle is crashworthy and there is no passenger
compartment intrusion, the layout of the interior is the main way that the
vehicle can influence the risk of injury. The environment must be
compatible with children’s needs during a collision. However, the field
study revealed that this can vary from vehicle to vehicle. Once again, it
was considered important for the project to address these issues.
The restraint system comprises a wheelchair restraint to hold the
wheelchair in place and an occupant restraint to prevent ejection and
reduce the risk of contact with the vehicle interior. It is vital that the
occupant restraint also absorbs and distributes the impact forces over
the strongest parts of a child’s body. This is partially explored by the
dynamic test in ISO 10542-1:2001, but again, the Standard does not
28
address occupant loading. As a result, there are several devices on the
market with a similar performance in terms of occupant excursion, but
they may perform differently in terms of occupant protection. For
instance, there are static belt systems, single inertia reel systems and
double inertia reel systems. Some include a third point, similar to the
upper anchorage point in cars, while others do not.
A very large test programme would be required to examine every
combination of wheelchair, vehicle and restraint system, particularly
when all the various types and adjustments are considered. TRL and
the DfT agreed a more pragmatic approach, which was to test a series
of common worst cases. This approach was used for the wheelchair
and vehicle issues; however, a different approach was used for the
restraint system.
Most wheelchair restraints on the market are four point webbing
restraints. These can include adjustable straps or retractable straps;
however, their performance is similar; hence this feature is unlikely to
influence the risk of injury. Clamps were available in the past, but are
now discontinued. With this in mind, a typical four point webbing
restraint with adjustable rear straps was used in all the forward facing
tests.
Most wheelchair occupant restraints include a lap and diagonal seat belt.
Some offer a better fit while others offer better energy absorption. TRL
considered the likely performance of different systems with children and
also their market share in the UK and Europe, but there was no clear
choice of which to use in the test programme. Following consultation
between TRL, the DfT and two of the leading manufacturers in the UK, a
surrogate occupant restraint was developed. The advantage of the
surrogate restraint was that it displayed the characteristics of several
production devices.
The surrogate occupant restraint consisted of a single inertia reel and an
upper anchorage point. The relative merit of an upper anchorage point
compared with a diagonal belt attached directly to the floor was
established for adults by Le Claire et al. (2003). It seemed likely that
dynamic tests to investigate this issue for children would make the same
observations. Diagonal belt anchorage location was not, therefore,
investigated in the test programme.
The surrogate occupant restraint, like many market products, could be
installed with a range of belt angles. There is a great deal of research
and knowledge to draw from when recommending the most appropriate
29
angles for seat belt webbing. Hence this aspect of the restraint system
was not investigated in the test programme.
In summary, a worst case approach was adopted when selecting the
wheelchair and vehicle issues to examine in the test programme. In
each test, the wheelchair was restrained by a common four point
webbing system while the occupant was restrained by a surrogate lap
and diagonal seat belt with upper anchorage. The seat belt was
installed to achieve the best fit possible for the particular wheelchair.
3.3
Test design – phase 1
As a starting point, the key wheelchair and vehicle design issues were
combined in order to determine which issues should be examined in
more depth. The next step was to take these issues and construct a
matrix for each type of wheelchair. Each matrix displayed all the tests
that would be required to complete the picture for the particular
wheelchair when it was used forward facing in an M1 or M2 vehicle. The
final step was to apply our knowledge of impact biomechanics and injury
mechanisms to identify priorities within each matrix. These priorities
would be used to develop solutions for all combinations of wheelchair
type, adjustment and child occupant size, etc. The following sections
outline this process.
3.3.1 Key issues
Tables 2 to 5 each represent a type of wheelchair. The first row in each
table lists the key issues for that device when it is used forward facing in
an M1 or M2 vehicle. There were a number of different options or
adjustments for each issue that might affect a child’s risk of injury in a
crash. The most important issues for a particular wheelchair were
selected on the basis of their frequency and likely influence on injury. In
each table, a tick means that the issue was examined in the test
programme and a square means that the most common or worst case
was adopted during the test set up, as appropriate. A shaded cell
means that no option or adjustment was possible for that wheelchair.
Table 2 describes the key issues for buggies when children travel
forward facing in M1 or M2 vehicles. Backrest angle, tilt angle and
occupant size were identified as having the greatest potential to affect
the injury mechanisms in a buggy and were therefore considered for the
test programme. When a backrest is reclined, the child’s pelvis is tilted
rearwards. This could increase the likelihood of the lap belt slipping off
the pelvis in a collision and loading the abdomen. When a backrest is
upright (i.e. 80 - 90˚), the lap belt can engage better with the pelvis, but
30
head excursion will be greater so the space in front of the wheelchair
becomes more important. When the seat and backrest are fixed but
tilted rearwards, there is also a risk that the lap belt could slip off the
pelvis. This risk might be mitigated by the angle of the seat, but it is
more likely that the seat cushion would compress or the buggy would
deform during the collision. The size of a child affects the way they load
the wheelchair and restraint system. It also affects the amount of clear
space needed in the vehicle around the wheelchair.
Most children using a buggy will have a positioning harness. This might
interfere with the path of the seat belt and could increase loads to the
child if the harness buckle rests under the belt. Although the presence
of a harness could be important, differences in design may not affect the
injury mechanisms greatly. A typical positioning harness was therefore
fitted in all tests with a buggy.
The seat is usually forward facing in a buggy, but some models have
rear facing seats while others have dual facing seats. Although the
effect of the seat orientation could be significant, only a few products
display this feature and it seems likely that most buggies will be used
with the seat installed forward facing. Seat orientation was not,
therefore, investigated in the test programme.
In some vehicles, the lower seat belt anchorages are positioned
outboard of the wheelchair. When this is the case, the contact area
between the lap belt and the pelvis is reduced and the path of the belt is
potentially more susceptible to obstruction from the side structure of the
wheelchair. Although the position of the lower anchorages could be
important for children in buggies, it was not possible to investigate the
issue with every wheelchair type.
Table 3 describes the key issues for manual wheelchairs when children
travel forward facing in M1 or M2 vehicles. Backrest angle, occupant
size and seat belt lower anchorage position were identified as having the
greatest potential to affect the injury mechanisms in a manual
wheelchair and were therefore considered for the test programme. As
discussed above, the backrest angle can affect the likelihood of the belt
remaining on the pelvis and it can affect the dummy excursion.
Occupant size can affect the wheelchair and restraint loading and the
space needed in the vehicle.
When the lower anchorages of the seat belt are outboard of the rear
wheels, the contact area between the lap belt and the pelvis is reduced.
It may also be the case that the lap belt needs to pass through the side
31
of the wheelchair. This may be difficult if large side guards are fitted.
Seat belt anchorage location was considered for the basic manual
wheelchair to examine whether there was an increased risk of abdomen
injury in a collision.
Although tilt angle may affect the likelihood of the belt remaining on the
pelvis, tilting manual wheelchairs (i.e. comfort wheelchairs) are not used
widely by children. This issue was not investigated in the test
programme.
Most manual wheelchairs are fitted with side guards to protect the child’s
clothes from spray thrown up by the wheels. Although they perform an
important function, they can complicate the fitment of the occupant
restraint in a vehicle. This aspect of the wheelchair design is not
necessarily covered when a wheelchair is assessed for ISO 717619:2001. Side guards were fitted, therefore, in all tests with manual
wheelchairs.
32
33
9
9
Occupant
size
Active user
Side guards
9
Tilt angle
9
Backrest
angle
Basic
Frame type
9
9
9
Supportive
Table 3 Manual wheelchairs – key issues
9
9
Lower
anchorages
9
Lower
anchorages
Occupant
size
9
Backrest
angle
Basic
Seating type
Table 2 Buggies – key issues
Postural
Seat
Tilt angle
belts
direction
Table 4 describes the key issues for electric wheelchairs when they
travel forward facing in M1 or M2 vehicles. Backrest angle, tilt angle and
occupant size were identified as having the greatest potential to affect
the injury mechanisms in an electric wheelchair and were therefore
considered for the test programme. As discussed above, the backrest
angle can affect the likelihood of the belt remaining on the pelvis and it
can affect the dummy excursion. Tilt angle may also affect the likelihood
of the belt remaining on the pelvis. Occupant size can affect the
wheelchair and restraint loading and the space needed in the vehicle.
The location of the lower seat belt anchorages can affect the contact
area between the lap belt and the pelvis; however, this was not identified
as a priority for electric wheelchairs.
Table 4 Electric wheelchairs – key issues
Backrest
angle
Electric
9
Tilt angle
9
Occupant
size
Lower
anchorages
9
Table 5 describes the key issues for supportive seating systems when
they travel forward facing in M1 or M2 vehicles. Moulded seating
systems were not investigated in the test programme. A child in a
moulded seat would not be accommodated easily by a standard
wheelchair tie-down and occupant restraint system. Furthermore,
current test dummies would not permit a full investigation of the
situation. Although a seat could be moulded to a dummy, it could not
reproduce the physical characteristics and issues associated with certain
medical conditions. The restraint of a child in a moulded seat may
require a bespoke solution to meet their particular needs. However, it
was impossible to examine individual cases within the project.
Tilt angle and occupant size were identified as having the greatest
potential to affect the injury mechanisms in a modular seating system
and were therefore considered for the test programme. As discussed
above, tilt angle may affect the likelihood of the belt remaining on the
pelvis. Occupant size can affect the wheelchair and restraint loading
and the space needed in the vehicle.
There are various types and levels of support used within modular
seating units. Although it would be desirable to understand the effects of
the different levels of support that are available, the number of tests
required for such an assessment was too high to consider for this
34
project. As such, this issue was not examined in detail, but a modular
seating system was used with the full range of support equipment fitted.
Most children using a modular seating system will have a positioning
harness. This could interfere with the occupant restraint system in the
vehicle, but the type of harness may not affect the injury outcome
greatly. A common positioning harness was fitted in all tests with
modular seating systems.
The position of the lower anchorages could be important for children in
seating systems because the contact area between the lap belt and the
pelvis is reduced and the path of the belt is potentially more susceptible
to obstruction from the side structure of the wheelchair. However, it was
not possible to investigate this issue for seating systems.
Table 5 Supportive seating systems – key issues
Seating
system
Tilt
angle
Modular
9
Supports
Postural
belts
Occupant Lower
size
anchorages
9
Moulded
3.3.2 Final test selection
Having identified the key issues that demanded further investigation, the
next step was to take these issues and construct a matrix for each type
of wheelchair. These are shown in Tables 6 to 9. Each matrix displays
all the tests that would be required to complete the picture for the
wheelchair when it is used forward facing in an M1 or M2 vehicle. While
it would be desirable to perform all the tests in each table, a number of
priorities were identified, which could be used to investigate the issues
and develop solutions for all combinations. A tick meant that a test was
selected for the final test matrix.
Table 6 shows all the tests that would complete the picture for children
travelling forward facing in buggies in M1 or M2 vehicles. Backrest
angle, tilt angle and occupant size were identified as key issues for both
types of buggy. The pelvis is tilted rearwards when a backrest is
reclined. Hence, there is a greater risk of the lap belt slipping off the iliac
crests and loading the abdomen. This risk is reduced when a backrest
is upright, but the risk of head injury might increase because a child’s
head is further forwards in the wheelchair space. There might also be a
risk of the lap belt loading the abdomen when the seat and backrest are
tilted rearwards.
35
Buggies are usually available with different seating dimensions and
some can be adjusted. The smallest seat size for a typical basic buggy
would hold a six year old child dummy and the largest size would hold a
ten year old dummy. The smallest seat size for a typical supportive
buggy would hold a three year old child dummy and the largest size
would hold a six year old dummy. There might, of course, be some
exceptions; however, these sizes seemed to reflect the seats in most
buggies.
If a basic buggy was used upright during an impact, the head excursion
with a larger child would be higher than the head excursion with a
smaller child. Although it could be argued that a smaller child would
have a lower tolerance to injury if head contact occurred, the larger child
represents the worst case in terms of the space required. The ‘upright’
test with the ten year old dummy was therefore selected as the priority in
Table 6.
If a basic buggy was reclined during an impact, the lap belt would be
more likely to slip off the pelvis if the child was small, because their iliac
crests would be less well developed. The ‘reclined’ test with the six year
old dummy was therefore selected as the priority.
A similar approach was taken for supportive buggies. If the backrest
was upright during a collision, a larger child would experience greater
head excursion than a smaller child. The ‘upright’ test with the six year
old dummy was therefore selected as the priority. If a supportive buggy
was reclined, the lap belt would be more likely to slip off the pelvis of a
small child. The ‘reclined’ test with the three year old dummy was
therefore selected as the priority.
Although some buggies are available with a tilting seat, TRL concluded
that the issues around tilt-in-space could be investigated better with
another type of wheelchair. As a result, no ‘tilted’ tests were prioritised
for either type of buggy.
36
Table 6 Buggies – test selection
Buggy
Backrest or tilt angle Dummy
6 year old
Upright
Basic
Priorities
Reclined
10 year old
9
6 year old
9
10 year old
6 year old
Tilted
10 year old
3 year old
Upright
Supportive Reclined
6 year old
9
3 year old
9
6 year old
3 year old
Tilted
6 year old
Table 7 shows all the tests that would complete the picture for children
travelling forward facing in manual wheelchairs in M1 or M2 vehicles.
Backrest angle, lower anchorage position and occupant size were
identified as key issues for manual wheelchairs.
As described above, the wheelchair backrest angle can influence the
head excursion and path of the lap belt in a collision. The position of the
seat belt lower anchorages can influence the contact area between the
pelvis and the lap belt and might make the path of the lap belt more
prone to obstructions from the wheelchair.
It was not the intention to carry out a large study of the effect of
anchorage location. There is a significant amount of research on the
subject and a range of angles for lap belts and lap belt anchorages are
outlined in ISO 10542-1:2001. Instead, the intention was to investigate a
specific situation observed during the field study whereby the lower
anchorages were relatively wide to allow access to a permanent
wheelchair space from the rear. This situation was represented by the
outboard anchorage tests in Table 7.
37
The inboard location in Table 7 refers to M1 vehicles and M2 vehicles
with a flexible wheelchair space where the lap belt anchorages are
attached to floor tracking behind the wheelchair. This was the normal
anchorage location for the test programme.
Basic manual wheelchairs usually have an upright backrest, but some
models can be fitted with a reclining backrest. Active user wheelchairs
have a small upright backrest only. Both types are usually available with
different seating dimensions and active user wheelchairs can sometimes
be adjusted. The smallest seat in a typical basic wheelchair with an
upright backrest would accommodate a child similar in size to a three
year old child dummy. The largest seat would accommodate a child
similar in size to a ten year old dummy. The smallest seat in a typical
basic wheelchair with a reclining backrest would accommodate a child
similar in size to a six year old dummy and the largest seat would
accommodate a child similar to a ten year old dummy. The
corresponding dummies for a typical active user wheelchair are a six
year old and a ten year old.
Children travelling in a basic upright manual wheelchair, with inboard
lower anchorages, might be at risk of abdominal injury from submarining
and head injury from head contact with the vehicle structure. Smaller
children are more likely to submarine because their pelvises are less
well developed; however, larger children experience greater head
excursion and are more likely, therefore, to strike the vehicle or another
wheelchair. In this instance, both the smallest and the largest needed to
be considered because they are very different in terms of their level of
development and therefore have different injury mechanisms. The three
year old and the ten year old were therefore selected as the most
important for children travelling in upright basic manual wheelchairs with
inboard lower seat belt anchorages.
When the lower anchorages are outboard of the wheelchair, there is an
added risk of poor lap belt fit and abdominal injury. The smallest
children are most at risk, so the three year old dummy was selected as
the most important for upright standard manual wheelchairs and
outboard lower seat belt anchorages.
The risk of submarining could be greater in reclining wheelchairs
because the pelvis is tilted rearwards. This could be an issue with both
inboard and outboard lower seat belt anchorages, but smaller children
are most at risk because their pelvises are less well developed and may
not fully engage with the seat belt. Tests with the six year old dummy
with inboard seat belt anchorages and also with outboard seat belt
38
anchorages are therefore selected as most important in a reclined
wheelchair.
The low backrest in active user manual wheelchairs places an additional
risk to the back and spine of a child due to the lack of support in
rebound. Larger children are likely to receive the least protection from
the small backrest; hence the ten year old was selected as the priority
for active user manual wheelchairs.
Table 7 Manual wheelchairs – test selection
Manual
wheelchair
Backrest
angle
Lower
anchorages
Inboard
Upright
Outboard
Basic
Inboard
Reclined
Outboard
Active
Upright
Inboard
Dummy
3 year old
6 year old
10 year old
3 year old
6 year old
10 year old
6 year old
10 year old
6 year old
10 year old
6 year old
10 year old
Priorities
9
9
9
9
9
9
Table 8 shows all the tests that would complete the picture for children
travelling forward facing in electric wheelchairs in M1 or M2 vehicles.
Backrest angle, tilt angle and occupant size were identified as key
issues for electric wheelchairs. Based on the dimensions of the seat,
electric wheelchairs are used by children that correspond in size to six
year old and ten year old child dummies.
A child restrained in an electric wheelchair with an upright backrest
during a collision would be at risk of head injury if their head struck the
interior of the vehicle. It is also possible that wheelchair displacement
might occur and apply loads to the child, which could result in chest and
abdomen injuries. Younger children would be more susceptible to the
risk of injury from wheelchair movement, while older children would
experience greater head excursion and hence a greater risk of head
contact. The level of risk perceived meant that it was necessary to
consider both the youngest and oldest children. The six year old and the
ten year old dummies were selected, therefore, for electric wheelchairs
with an upright backrest. While it would be desirable to perform tests
39
with reclined or tilted electric wheelchairs, it was decided not to include
these devices after taking their prevalence for children into account.
Table 8 Electric wheelchairs – test selection
Wheelchair
Backrest or
tilt angle
Upright
Electric
Dummy
Priorities
6 year old
9
10 year old
9
6 year old
Reclined
10 year old
6 year old
Tilted
10 year old
Table 9 shows all the tests that would complete the picture for children
travelling forward facing in supportive seating systems in M1 or M2
vehicles. Tilt angle and occupant size were identified as key issues for
supportive seats. Based on the dimensions of the seat, these are used
by children that correspond in size with a range of child dummies from
the three year old up to the ten year old.
If a seating system was used with an upright backrest during a collision,
a child would be at risk of head injury if their head struck the vehicle
interior. They would also be at risk of abdominal injury if the seat belt
did not remain on the top of their thighs. Younger children are
particularly at risk from poor belt fit and performance while older children
experience greater head excursion. Both the youngest and oldest
children needed to be considered to investigate both these risks
because the injury mechanisms are different. The three year old dummy
and the ten year old dummy were selected, therefore, as the priorities for
supporting seating units with upright bases.
If a seating system was used with a tilt-in-space base during a collision,
a child might be at risk of abdominal injuries due to submarining.
Younger children are more likely to submarine; however, larger children
would apply greater loads to the wheelchair seat base, which could
increase their risk of submarining. Both the three year old and the ten
year old dummies in a fully tilted wheelchair base were selected,
therefore, as the priorities for seating systems with tilt-in-space
wheelchair bases. While it would be desirable to perform tests across
the full range of seat angle adjustment, fully tilted represented the
greatest risk.
40
Table 9 Supportive seating systems – test selection
Seating
system
Tilt angle
Dummy
3 year old
Upright
Priorities
9
6 year old
Modular
Tilted
10 year old
9
3 year old
9
6 year old
10 year old
9
3.3.3 Test matrix
The final step was to compile the tests identified as priorities from Tables
6 to 9. These are shown in Table 10, along with some baseline tests
with the dummy restrained in a vehicle based restraint system. These
tests represented the minimum required to investigate the key issues.
This vehicle scenario was intended to represent the range of vehicles in
which wheelchairs travel in this way, from small converted vehicles (M1
vehicles) for the private market or for the taxi market up to minibuses
(M2 vehicles) used for community transport.
In many ways, the wheelchair user travels in the same way in each of
these M1 and M2 vehicles. The wheelchair is held in place, usually by
means of a four point webbing restraint system attached to tracking in
the floor of the vehicle. The wheelchair user wears a seat belt, which is
also attached to this tracking. Occupant contact with the vehicle interior
is possible during an impact, but there is no initial direct contact between
the wheelchair (or user) and the vehicle walls or bulkheads. There was
no need, therefore, for any representation of the interior surfaces of the
vehicle in the test programme. The risk of contact was examined from
dummy displacement measurements.
In some M1 vehicles, the lower seat belt anchorages are positioned
outboard of the wheelchair to allow rear wheelchair access to the
vehicle. When this is the case, it is possible that the lap part of the seat
belt will fit less well on the child’s abdomen. While it was desirable to
combine M1 and M2 vehicles, this issue was also examined separately
as shown in Table 10.
41
Whereas a wheelchair user may travel in similar circumstances
irrespective of the vehicle category, this is not the case for other
children. For instance, the vehicle seat in an M1 vehicle is different to
that in an M2 vehicle and may, therefore, affect the level of protection
afforded to the child. Furthermore, there is a legal requirement to use an
additional child restraint system in an M1 vehicle (with some limited
exceptions), but in an M2 vehicle, a child restraint must be used only if
one is available.
The implication for the test programme was that a high number of
baseline tests would be needed to cover each scenario. TRL and the
DfT agreed a more pragmatic approach in order to maximise the number
of tests available for the wheelchairs. It seemed likely that the effect of
the vehicle seat and/or child restraint would be greatest with the three
year old dummy. It was agreed, therefore, that the main baseline tests
would use a minibus seat with the three, six and ten year old dummies.
However, additional tests would be carried out with the three year old
dummy seated in a child restraint on a car seat and with the three year
old dummy seated in a child restraint on a minibus seat. If the results
displayed significant differences, then the possibility of further baseline
tests would be discussed.
42
Table 10 Test matrix – M1 or M2 forward facing
Wheelchair
Buggy – basic
Buggy – supportive
Backrest or Lower
tilt angle
anchorages
Upright
Reclined
Inboard (M2)
Upright
Reclined
Upright
Manual – basic
Inboard (M2)
Manual – active user Upright
Outboard (M1)
Inboard (M2)
Outboard (M1)
Inboard (M2)
Electric
Inboard (M2)
Reclined
Supportive seating
system – modular
Upright
Upright
Inboard (M2)
Tilted
M1 vehicle seat (car seat) and child restraint
M2 vehicle seat (minibus seat) and child restraint
M2 vehicle seat (minibus seat)
Dummy
10 year old
6 year old
6 year old
3 year old
3 year old
10 year old
3 year old
6 year old
6 year old
10 year old
6 year old
10 year old
3 year old
10 year old
3 year old
10 year old
3 year old
3 year old
3 year old
6 year old
10 year old
3.3.4 Test set up
Figure 12 shows the set up in typical tests with forward facing
wheelchairs. The image on the left shows a baseline test with the six
year old dummy, while the image on the right shows a corresponding
wheelchair test.
The wheelchairs were restrained by a production model four point
webbing system that was secured to the floor by aluminium track fittings.
The dummy was restrained independently by a three point seat belt.
The seat belt included an inertia reel and an upper anchorage point.
The seat belt was a surrogate model developed for the test programme
by a manufacturer of commercial wheelchair tie-down and occupant
restraint systems through consultation with another manufacturer of
wheelchair and occupant restraint systems. The performance of the
surrogate seat belt was verified with the four point webbing restraint
during a dynamic test according to ISO 10542-1:2001. The wheelchair
43
tie-down and occupant restraint system was replaced following each
test.
All test pieces were installed according to the manufacturer’s instructions
and to the ISO Standards, unless there was a strong reason for not
doing so. Any deviations from the Standards were documented. In
particular, the occupant restraint was installed to achieve the best
possible belt path for the child dummy, although it was recognised that
this was not always the case in the real world. However, it was not
within the scope of the project to investigate potentially unfavourable belt
routes and misuse. Reclined or tilted wheelchairs were adjusted to the
limit of the mechanism. This produced a backrest angle of around 30˚ to
the vertical.
Figure 12 Forward facing six year old child dummy restrained in a
vehicle seat (left) and electric wheelchair (right)
The main aim of the tests was to investigate occupant loading in a range
of common children’s wheelchairs and compare these loads with a
vehicle seated baseline. This included the measurement of seat belt
forces.
In one test, the wheelchair anchorage forces were recorded. The
electric wheelchair with the ten year old dummy was selected as the
priority for measuring the forces at the restraint anchorages. Previous
research with adult dummies proposed vehicle anchorage strength
requirements for wheelchair restraint systems (Le Claire et al., 2003).
The heaviest wheelchairs for children are likely to generate lower forces
than wheelchairs for adults. Although separate requirements for
vehicles which depend on the weight of the occupant or of their
wheelchair would introduce a range of issues, it was considered useful
to obtain some comparative data. For instance, it might be considered
inappropriate to ask someone to buy a larger or stronger vehicle than
44
necessary, if it is a privately owned vehicle used to carry a child. It might
be appropriate, in these circumstances, to have less stringent
requirements for anchorage strength.
3.4
Findings – phase 1
3.4.1 Relative safety of current situation
The test programme highlighted a number of issues for children
travelling forward facing in a wheelchair in an M1 or an M2 vehicle.
These issues related to the geometry of the occupant restraint, the
stiffness of the wheelchair and the environment within the vehicle.
The seat belt was installed to achieve the best possible fit for the child
dummy in each test (within the limits of possibility when a tracking based
system is used). Nevertheless, the lap part of the belt tended to rest
higher on the pelvis and abdomen than desirable. The path of the belt
was influenced by the location of the anchorages in the tracking and by
the design of the wheelchair. Film analysis revealed that the belt loaded
the abdomen of the dummy in most tests. The forces in a lap belt would
result in serious abdominal injuries for a child in these circumstances.
The initial position of the belt was important, but another factor was the
deformation of the wheelchair during the impact. When the dummy was
seated on a vehicle seat, it was noted that the path of the lap belt could
be improved. However, the belt remained on the pelvis during the
impact tests and did not load the abdomen of the dummy.
The stiffness of the wheelchairs affected their capacity to withstand the
forces of the impact. A number of wheelchairs deformed during the tests
to the point where additional loads were transferred to the dummy. In
addition, the likelihood of the belt loading the abdomen increased when
the wheelchair deformed. In contrast, the vehicle seat maintained its
integrity during the tests and although the management of the dummy’s
loads could be improved, the dummy was not exposed to any additional
loading in vulnerable body regions.
The environment created to represent a typical M1 or M2 vehicle did not
include a head and back restraint. As a result, the dummy received no
additional support above that provided by the wheelchair backrest or
headrest (when provided). In the absence of an effective head restraint,
the dummy head extended rearwards during the rebound phase of the
impact. A child travelling in this way would be exposed to the risk of
head contact with the interior of the vehicle and soft tissue injuries to the
neck. A child in a vehicle seat would usually be provided with a head
and back restraint and would not, therefore, be exposed to these risks.
45
The amount of space in front of the wheelchair user is another important
aspect of the environment within a vehicle. The dummy displacement
measurements were used to derive space requirements for children in
wheelchairs.
The following sections examine the effects of restraint geometry,
wheelchair stiffness, head and back restraint and occupant space in
more depth.
3.4.2 Effect of restraint geometry
An effective occupant restraint system absorbs and distributes the
restraint forces over the strongest parts of the body. The anterior
superior iliac spines of the pelvis (i.e. the wings) provide an anchor for
the lap part of a seat belt and are strong enough to withstand the forces
in adults and older children. However, it is important that the belt fits
correctly. This means it must pass low over the hips, touching or even
lying flat over the thighs. The shoulder provides an anchor for the
diagonal part of a seat belt and restrains the upper torso. This is
important to prevent rapid bending and stretching of the spine, which
has been linked to the risk of injury in lap only seat belts.
A restraint system designed for adults will not fit children so well.
Furthermore, their underdeveloped anatomy means that their natural
anchor points are smaller and may not engage with the seat belt in the
same way. Younger children are most at risk, but the key development
of the pelvis, the formation of the iliac wings, is not complete until at
least ten years of age. Since the level of protection is likely to change as
a child develops, this section examines the effect of restraint geometry
at each dummy ‘age’ in the test programme.
It must be noted that the Hybrid III Series of child dummies was not
equipped with instrumentation in the abdomen. Hence the investigation
of the effects of seat belt geometry on the protection afforded to the
abdomen was based on analysis of high speed films of each test. It
must also be noted that the abdomen of the dummy is stiffer than that of
real children; hence any effects may be greater in the real world.
Figure 13 shows the path of the seat belt during selected tests with the
three year old dummy. The image on the left of the first row shows the
dummy seated on a booster seat on a standardised test seat that
represents a modern passenger car. The image on the right of the first
row shows the dummy seated directly on a minibus seat. The image on
46
the left of the second row shows the dummy seated on a booster seat on
a typical minibus seat, and the remaining images are selected
wheelchair tests to illustrate the findings.
M1 vehicle seat and booster
M2 vehicle seat
M2 vehicle seat and booster
Seating system – tilt-in-space
Basic manual wheelchair
Supportive buggy
Figure 13 Seat belt geometry in selected tests with three year old
dummy
47
Figure 13 shows that the seat belt remained on the three year old
dummy pelvis during the vehicle seated tests. However, when the
dummy was restrained in a wheelchair, the lap belt loaded the abdomen.
This occurred due to obstructions caused by the wheelchair structure or
due to deformation of the wheelchair. For instance, the supportive
seating system with tilt-in-space wheelchair base included large hip
support pads. This meant that it was impossible to achieve the ideal
path for the lap part of the belt. In addition, the tilt-in-space facility did
not simply rotate about the seat axis. Instead, it moved the pelvis
downwards in an arc by approximately 100 mm with respect to the
horizontal. The anchorages could not be moved forwards due to the
wheelchair tipping levers; hence the side view belt angle was lower than
desired at approximately 45˚. These factors, combined with the angle of
the pelvis and the compression of the seat cushion, led to the dummy
submarining under the lap belt.
Another example of an obstruction caused by the wheelchair structure
was found with the manual wheelchair. The wheelchair was fitted with
side guards attached to the seat and backrest. The lap belt had to pass
over the top of the side guards, which affected the position of the belt on
the dummy pelvis. Finally, the supportive buggy was also fitted with hip
pads that obstructed the path of the lap belt. In addition, the five point
positioning harness in this wheelchair made it harder to fit the seat belt
over the pelvis. During the impact, the buggy compressed, which also
contributed to the submarining illustrated in the figure.
Figure 14 shows the path of the seat belt during selected tests with the
six year old dummy. The image on the left of the first row shows the
dummy seated on a typical minibus seat and the remaining images are
selected wheelchair tests to illustrate the findings.
The seat belt remained on the six year old dummy’s pelvis during the
vehicle seated test. However, problems were observed once again with
the path of the lap belt during the wheelchair seated tests. For example,
although the basic buggy did not obstruct the path of the lap part of the
belt to the same extent as some of the other wheelchairs, the buggy
deformed during the impact resulting in the submarining shown in the
figure.
The six year old dummy also submarined during the tests with the
reclined manual wheelchair. This occurred irrespective of the distance
between the lap belt anchorages and was a result of the dummy pelvis
tilting rearwards in the reclined seat.
48
M2 vehicle seat
Basic buggy
Reclined manual wheelchair
Reclined manual wheelchair –
outboard anchorages
Figure 14 Seat belt geometry in selected tests with six year old dummy
Figure 15 shows the path of the seat belt during selected tests with the
ten year old dummy. The image on the left of the first row shows the
dummy seated on a typical minibus seat and the remaining images are
selected wheelchair tests to illustrate the findings.
The seat belt remained on the ten year old dummy pelvis in the vehicle
seated test and in the tests with the manual wheelchair and active user
wheelchair. It also remained on the pelvis during the test with the
upright supportive seat, although this device was fitted with knee blocks.
However, the seat belt loaded the ten year old dummy abdomen in
several wheelchair seated tests. Some of these are illustrated in the
figure. The same issues emerged: compression of the wheelchair
resulted in forward and downward motion of the dummy under the lap
part of the belt, or poor geometry brought about by obstructions in the
side of the wheelchair.
49
M2 vehicle seat
Basic buggy
Supportive seat – tilt-in-space
Electric wheelchair
Figure 15 Seat belt geometry in selected tests with ten year old dummy
The test programme highlighted that children restrained in wheelchairs
could be at risk of abdomen injury during a collision. Although the seat
belt geometry could also be improved for children in vehicle seats, the
lap belt remained on the dummy pelvis during these tests. The path of
the lap belt during the impact was influenced by the side structure of the
wheelchair and by the capacity of the wheelchair to withstand the impact
test.
ISO 7179-19:2001 includes a test procedure to assess the extent to
which a wheelchair can accommodate vehicle anchored occupant
restraints. However, the test procedure is currently voluntary and will
not necessarily address submarining resulting from wheelchair
compression or deformation. A better solution might be to establish a
performance criterion for abdomen penetration during an impact test.
The surrogate occupant restraint was designed to remove any
influences of restraint design. It was set up according to the ISO
Standards and to achieve the best fit possible for each wheelchair.
Nevertheless, it is recognised that wheelchair manufacturers may
50
recommend that a specific make or model of wheelchair tie-down and
occupant restraint system is used with their product. It is also
recognised that these recommended commercial restraints may differ in
fit and performance from the surrogate restraint.
3.4.3 Effect of wheelchair stiffness
All wheelchairs used in the test programme (except the active user
wheelchair) were suitable for use forward facing in a vehicle, as stated in
their product literature. Although the UNECE Regulation 44 sled test
conditions were slightly more stringent than the ISO Standards, it was
surprising to find that several of the wheelchairs were unable to
withstand the impact test. This was generally the case with the six year
old and ten year old dummies, but there were also examples with the
three year old, as shown in Figure 16. The image on the left shows the
dummy and the modular seating system following a test and the image
on the right shows the supportive buggy during a test.
The modular seating system in the image on the left of Figure 16 was
fitted to a base supplied by a different manufacturer. There were
dedicated attachment points and all fitting was carried out by the seating
manufacturer. In addition, the mass of the seating system and dummy
were well within the limits stated for the base within its product literature.
The seating system had been tested according to ISO 16840, which
includes a dynamic test with a surrogate base. The base had been
tested with its own seating according to ISO 7176-19:2001. It seems
that presence of the modular seating system affected the performance of
the base in a manner that would not be evaluated by the ISO Standards.
The dummy measurements were generally quite low in the test;
however, it is likely that a child in these circumstances would receive
multiple fractures, which are not readily predicted by crash test
dummies. There would also be a greater risk of the child’s head striking
the interior of the vehicle.
The supportive buggy in the image on the right of Figure 16 was able to
withstand the impact; however, it compressed forwards and downwards.
This contributed to the lap belt slipping off the pelvis and loading the
abdomen. In addition, the peak head and neck loads corresponded to
the maximum compression of the wheelchair. The loads were usually
higher than the baseline test and exceeded some published injury limits.
For example, the head acceleration exceeded the M2 vehicle seat
baseline test by 35 percent. The neck tensile force exceeded this
baseline by 90 percent and the limit proposed by Mertz et al. (2003) by
194 percent.
51
Figure 16 Wheelchair stiffness in selected tests with three year old
dummy
Some examples with the six year old dummy are shown in Figure 17.
The image on the left shows the basic buggy during the impact and the
image on the right shows the supportive buggy. Both buggies deformed
during the test, which contributed to the lap part of the seat belt loading
the abdomen. The basic buggy seemed to absorb some of the forces
without transferring them to the occupant. Nevertheless, it would be
undesirable for the structure of a wheelchair to fail in this way. Some of
the neck loads with the supportive buggy displayed a period of increased
magnitude that seemed to correspond to the peak compression of the
device. The loads were usually higher than the baseline test and
exceeded some published injury limits. For example, the neck tensile
force exceeded the baseline by 60 percent and the limit proposed by
Mertz et al. (2003) by 154 percent.
Figure 17 Wheelchair stiffness in selected tests with six year old dummy
Some examples with the ten year old dummy are shown in Figure 18.
The image on the left shows the basic buggy during the impact and the
52
image on the right shows the electric wheelchair. Both devices
compressed during the impact, resulting in the dummy submarining
under the lap part of the seat belt. In the case of the electric wheelchair,
an attachment between the seat and the base failed during the forward
motion of the dummy and resulted in rotation of the seat during rebound.
It was interesting to note that the electric wheelchair performed
adequately with the six year old dummy.
Figure 18 Wheelchair stiffness in selected tests with ten year old dummy
Most wheelchairs in the test programme deformed to some extent,
resulting in additional loading to the dummy. The effects varied by
wheelchair type, but typically led to greater dummy accelerations and
forces or greater loading to vulnerable body regions such as the
abdomen. Children’s wheelchairs derived from adults’ wheelchairs
seemed to be stronger than those devices developed specifically for
children. This was probably because adult versions had been designed
to withstand the loads with a 50th percentile dummy.
3.4.4 Effect of head and back restraint
Few vehicles provide a head and back restraint for wheelchair users.
The wheelchair backrest (and headrest if one is fitted) is therefore the
main support for the occupant during the rebound phase of an impact.
The backrest must be capable of withstanding the forces from the
occupant to reduce the risk of body contact with the interior of the
vehicle. Backrest strength requirements can be derived from general
requirements about the position of the dummy and signs of wheelchair
failure following the dynamic test in ISO 7176-19:2001. There is also a
limit placed on the rearward head displacement of the dummy during the
test. However, this limit allows significant neck extension. A child in a
wheelchair could therefore be at risk of injury even if their wheelchair
backrest remains intact. This was examined in the test programme.
53
Figure 19 shows some examples with the three year old dummy. The
image on the left of the top row shows the dummy seated on a booster
seat on a standardised test seat that represents a modern passenger
car. The image on the right of the top row shows the dummy seated
directly on a minibus seat and the remaining images are selected
wheelchair tests to illustrate the findings.
When the dummy was seated in a vehicle seat (with or without a
booster), the head and neck were supported through the rebound phase.
If a child was travelling in this way, there would be no possibility of
contact with the vehicle (or other occupants) behind the seating position
and minimal neck extension. When the dummy was seated in the
modular seating system with a tilt-in-space wheelchair, the head rose
above the top of the head- and backrest and the neck extended
rearwards. This was due to the poor belt geometry combined with the
angle of the seat, which led to the dummy ramping up the backrest. The
dummy head remained within the footprint of the wheelchair.
Nevertheless, a child would be exposed to the risk of contact with the
vehicle interior. This risk could be mitigated by the provision of
adequate space around the wheelchair, but that would not address the
neck extension. Although the neck forces and extension moments were
low during this part of the impact, the neck was bending below the level
of the load cell. It is possible, therefore, that there is a further injury
mechanism that the dummy is not able to predict.
When the three year old dummy was seated in the manual wheelchair,
the push handle folding mechanism failed. As the figure shows, the
dummy tended to move towards the left hand side of the sled during
rebound, possibly because the upper anchorage point was on that side.
As a result, the dummy loaded the left push handle to a greater extent
than the right push handle. If this occurred in a real vehicle, a child
would be at greater risk of striking the interior surfaces.
54
M1 vehicle seat and booster
M2 vehicle seat
Seating system – tilt-in-space
Basic manual wheelchair
Figure 19 Head and back restraint in selected tests with three year old
dummy
Some further examples are shown in Figure 20 with the six year old
dummy. The vehicle seat supported the head and neck of the dummy,
so the figure shows two examples with the dummy seated in a
wheelchair. The image on the left shows a test with an electric
wheelchair and the image on the right shows a test with a reclined
manual wheelchair.
The backrest of the electric wheelchair withstood the loading from the six
year old dummy, but the neck extended rearwards. The dummy head
remained within the footprint of the wheelchair and restraint system, but
a child travelling in this way would be placed at greater risk of head
contact in some vehicles. Furthermore, the level of neck extension was
considerably greater than the vehicle seated test.
The reclined wheelchair was fitted with a headrest, but this offered
limited protection during the impact test. As the figure shows, the
55
headrest was pushed away as the dummy ramped further up the
backrest.
Electric wheelchair
Reclined manual wheelchair
Figure 20 Head and back restraint in selected tests with six year old
dummy
Figure 21 shows some tests with the ten year old dummy. Once again,
the vehicle seat supported the head and neck of the dummy, so the
figure shows two examples with the dummy seated in a wheelchair.
The image on the left shows the dummy seated in a manual wheelchair
and the image on the right shows the dummy seated in the active user
wheelchair.
When the dummy was seated in the manual wheelchair, the push handle
folding mechanism failed during the test, which was also observed with
the three year old dummy. If this occurred in a real vehicle, the child
might strike their head on the interior. Furthermore, their neck could
extend rearwards, perhaps leading to injury.
The dummy was not contained during the rebound phase of the test with
the active user wheelchair. This wheelchair was not designed to be
used in a vehicle while occupied; however, it was included in the test
programme to examine the issues. The test demonstrated that active
wheelchairs can withstand the forces during a collision, but that the
occupant is not protected by the wheelchair backrest during rebound.
The low backrest is an important part of the design of active user
wheelchairs and is likely to be appreciated by users.
56
Basic manual wheelchair
Active user manual wheelchair
Figure 21 Head and back restraint in selected tests with ten year old
dummy
A child restraint system (or a vehicle seat) will support a child’s head and
neck during the rebound phase of a front impact. This reduces the risk
of head contact with any vehicle structures behind the child and reduces
the risk of neck injuries associated with extension. The buggies used in
the test programme provided similar levels of support as the booster
seat (and/or the vehicle seat), due to the height of their backrests.
However, a number of issues emerged when the dummies were seated
in other wheelchair types.
The strength of the backrest and any folding mechanism is critical. As
the tests showed, if the backrest fails, the child could be thrown
rearwards during a collision with the risk of head contact with the vehicle
interior. It is very important to protect the head from contact because the
bones in a child’s skull are not developed fully, hence low levels of
loading can result in relatively high deformations of the skull and brain.
When the backrest remains in position, the rearward head displacement
and therefore the risk of head contact is reduced to some extent.
However, the tests demonstrated that the head moves rearwards
extending the entire neck. Uncontrolled movement of the head in this
way is likely to result in soft tissue neck injuries. Although these injuries
are sometimes classified as relatively minor, they can lead to long term
problems.
Wheelchair headrests are not designed to be head restraints and did not
perform that function in the impact tests. In some cases, the dummy
ramped up the wheelchair backrest missing the headrest altogether,
while in other cases the head pushed the headrest away.
57
The test programme has highlighted that children in some wheelchairs
do not receive a comparable level of protection as children travelling in a
child restraint or even a vehicle seat. This could be addressed by
providing a head and back restraint for all wheelchair users in vehicles.
A head and back restraint within the vehicle might be appropriate for
manual and electric wheelchairs; however, there would need to be a
wheelchair integrated solution for wheelchairs with supportive seating.
This is because these wheelchairs may be fitted with a headrest for
postural support which would prevent the child’s head from being
positioned against a head and back restraint in the vehicle.
3.4.5 Anchorage loading
One of the tests described in Section 3.3.3 was used to investigate the
loading on the vehicle anchorages. This test used the ten year old
dummy restrained in the electric wheelchair.
The longitudinal forces (i.e. x axis) measured in the test were resolved to
45˚ to provide a consistent basis for a static strength test for a vehicle
intended for children’s wheelchairs only. The longitudinal component of
the force was the largest in magnitude and therefore represents the
worst case. Table 11 shows the resolved forces.
Table 11 Restraint anchorage loads
Wheelchair restraint – front
Combined wheelchair and occupant restraint – rear
Occupant restraint – upper anchorage
Force (kN)
2.65
28.50
7.30
The loads in Table 11 were derived from a dynamic test using a rigid
sled platform. The floor of the sled did not flex or deform during the
impact in the way that a vehicle floor might under this type of loading.
However, Forinton and Glyn-Davies (2004) demonstrated that any load
attenuation due to vehicle deformation is likely to be negligible.
3.4.6 Occupant space requirements
The risk of injury resulting from body contact with the vehicle interior can
be reduced if there is sufficient space for the wheelchair and occupant.
Figure 22 shows the minimum space required for forward facing children
in wheelchairs in M1 and M2 vehicles. The space was derived from
head, knee and ankle excursion measurements with the Hybrid III ten
year old dummy.
58
Figure 22 Occupant space
The minimum space is the perimeter of the combined shape of the three
sections in the figure. The red section represents the space required for
the head, the green section represents the space required for the knee
and the blue section represents the space required for the ankle. In
each section, the shaded area denotes the initial position of each body
part before the impact.
All vertical distances were taken from the floor of the sled, while the
horizontal distances were taken from the upper anchorage position.
These planes are represented by the black lines in the figure.
3.5
Test design – phase 2
Following the first phase of testing, it was clear that the test results could
be used to make practical recommendations about the carriage of
children in wheelchairs in M category vehicles. However, it was also
clear that some further tests would be a useful means of supporting the
recommendations, where necessary.
TRL and the DfT agreed that recommendations could be made to
address the issues related to wheelchair stiffness, head and back
restraint, anchorage loads and occupant space without further testing.
Recommendations could also be made to address the issues related to
59
occupant restraint geometry, but two proposals emerged that required
further evaluation. The following sections describe these proposals in
more detail and outline the process to develop the test matrix for the
second phase of testing.
3.5.1 Key issues
The first phase of the test programme highlighted that the geometry of
the occupant restraint is an important issue for children who travel while
seated in their wheelchairs. Although the occupant restraint was
installed according to ISO 10542-1:2001 and to achieve the best fit
possible around the dummy, the lap part of the belt loaded the abdomen
in some tests. The capacity of the wheelchair to withstand the impact
without deforming was important, but another factor was the initial
position of the belt. The tests revealed that the belt was more likely to
load the abdomen when the ideal path over the upper thighs was
obstructed by the side of the wheelchair. The obstructions included side
guards to prevent splashing from the wheelchair wheels and hip pads to
position the child’s pelvis.
Side guards and hip support pads both have an important function. It
would be inappropriate, therefore, to remove them from wheelchairs.
However, it would be relatively straightforward to design the wheelchair
to guide the seat belt more easily. Booster seats are an ideal example
of what can be achieved. These often include a side structure, but
incorporate guides that ensure that the lap part of the seat belt passes
over the top of the thighs. These guides also keep the lower part of the
diagonal belt adjacent to the pelvis. An additional guide ensures that the
upper part of the diagonal belt lies flat on the centre of the shoulder and
crosses the centre of the chest. The potential of seat belt guides to
improve the path of the lap belt and therefore reduce the risk of
abdomen loading was examined in the second phase of the test
programme.
The first phase of the test programme also highlighted that the
positioning harnesses and straps in some wheelchairs can complicate
the fitment of the seat belt. In some cases, the positioning belts already
occupied the ideal route for the seat belt. In other cases, the positioning
straps and buckles were placed in an inappropriate place, resulting in
additional loads being applied to the dummy.
It would be inappropriate to remove these harnesses and straps;
however, they could be designed to provide restraint and distribute the
forces in a collision. This would remove the need for an additional seat
60
belt and might offer improved occupant protection by distributing the
restraint forces more effectively. There would be a number of practical
and technical issues to consider. Nevertheless, the potential benefits of
a wheelchair integrated harness were examined in the second phase of
the test programme.
3.5.2 Final test selection
Two proposals were made for further investigation in the second phase
of impact testing: a seat belt guide and an integrated crash tested
harness. The intention was to repeat tests from the first phase of the
test programme using wheelchairs that were modified to include a seat
belt guide or an integrated harness. This would allow the results to be
compared with the unmodified baseline test.
As a starting point, the wheelchairs that would benefit most from these
proposals were included in a matrix. This is shown in Table 12. The
matrix displays all the tests that could be carried out to evaluate each
proposal fully. Buggies were excluded due to their structural
performance in the first phase of testing. A number of other wheelchairs
did not display sufficient strength in the first phase to be considered.
These were highlighted by shading in the table. While it would be
desirable to perform all the tests in the matrix, a number of priorities
were identified. A tick meant that the test was selected for the final test
matrix.
The greatest obstruction of the lap part of the seat belt was observed
with the supportive seating system with tilt-in-space wheelchair base.
The test with the three year old dummy was selected as the priority due
to its small pelvis. It was anticipated that (in our sample) this
combination of wheelchair type and occupant size would benefit most
from the seat belt guide. In fact, the design of the seating system used
with the tilt-in-space wheelchair was similar to buggies and other seating
systems on the market. TRL was confident, therefore, that the findings
could be applied to other wheelchairs.
The supportive seating system with tilt-in-space wheelchair base and
three year old dummy were selected to investigate the potential of an
integrated harness. The three year old dummy was expected to benefit
most from a wheelchair integrated harness. A test with the ten year old
dummy was also selected to examine a potential worst case in terms of
the additional loads applied to the wheelchair.
61
Table 12 Phase 2 – test selection
Proposal
Wheelchair
Seat belt guide
Seating
system –
modular
Manual –
basic
Integrated
harness
Seating
system –
modular
Backrest or
tilt angle
Upright
Tilted
Upright
Upright
Tilted
Dummy
Priorities
3 year old
10 year old
3 year old
10 year old
3 year old
10 year old
3 year old
10 year old
3 year old
10 year old
9
9
9
3.5.3 Test matrix
The tests selected for the second phase of the impact test programme
are shown in Table 13. The vehicle environment created on the impact
sled was identical to that created for the first phase of the testing.
Table 13 Test matrix – M1 or M2 forward facing phase 2
Wheelchair
Seating system
Backrest or tilt angle
Dummy
Upright
10 year old
3 year old
3 year old
Tilted
3.5.4 Test set up
Figure 23 shows the set up for the tests in the second phase of the
impact test programme. The image on the left shows the three year old
dummy in the supportive seating system with a tilt-in-space wheelchair
base. The seating system was modified to guide the lap and diagonal
parts of the seat belt. The image in the centre also shows the three year
old dummy in the supportive seating system with a tilt-in-space
wheelchair base. However, this time the seating system was modified to
include a five point harness. The image on the right shows the ten year
old dummy in the supportive seating system with an upright base. This
seating system was also modified to include a five point harness.
62
Figure 23 Wheelchair modifications and set up for phase 2 of impact
testing
The wheelchairs were restrained by the same production model four
point webbing system described in Section 3.3.4. The dummy was
restrained by the surrogate seat belt described in Section 3.3.4 during
the test to investigate seat belt guides. The integrated harnesses were
provided by a child restraint system manufacturer in consultation with a
supportive seating manufacturer.
3.6
Findings – phase 2
3.6.1 Effect of restraint geometry
Figure 24 shows a comparison between the lap belt path over the
dummy in a supportive seating system and a seating system modified
with a seat belt guide. The seating system was attached to an identical
tilt-in-space wheelchair base in each test. As the figure shows, the path
of the lap belt was improved in the modified wheelchair. This was due to
the lap belt being positioned lower on the dummy, thus reducing the
loading on the abdomen.
63
With seat belt guides
Without seat belt guides
Figure 24 Seat belt geometry in tests with three year old dummy in a
seating system and tilt-in-space wheelchair
A clear improvement in belt path and abdomen loading was achieved
when seat belt guides were added to the seating system. However, the
advantage was limited by the design of the tilt-in-space wheelchair base
in this restraint system configuration. This was because it was
necessary to locate the anchorages further rearwards (with respect to
the wheelchair) than would usually be the case. This was done to
prevent the straps from fouling against the tipping levers on the
wheelchair. The resulting side view angle of the lap belt was therefore
lower than desirable (at around 40˚ from the horizontal) and affected the
capacity of the belt to engage with the pelvis of the dummy.
The position of the diagonal belt path was also improved throughout the
impact, as the upper belt guide maintained the favourable routing across
the dummy’s torso. These factors also assisted in reducing the dummy
rearward excursion. This is shown in Figure 25. Reducing the occupant
rearward excursion reduces the risk of the occupant’s head striking an
object behind the wheelchair, e.g. part of the vehicle interior. The
maximum rearward head excursion for the unmodified version was
347 mm. The maximum rearward head excursion for the version with
the seat belt guide was 218 mm. This is a decrease in rearward head
excursion of 37 percent.
64
Figure 25 Rearward head excursion in tests with three year old dummy
in a seating system and tilt-in-space wheelchair
Figure 26 shows a comparison between the lap belt path over the three
year old dummy in a seating system and a seating system modified to
incorporate an integrated five point harness. The seating system was
attached to an identical tilt-in-space wheelchair base in each test.
Figure 27 shows a comparison between the lap belt path over the
ten year old dummy in a seating system and a seating system modified
to incorporate an integrated five point harness. The seating system was
attached to an identical base in each test. As the figure shows, the five
point harness provides preferable restraint routing as the loads are
distributed more evenly over the strongest areas of the child’s anatomy.
Three point seat belt
Integrated five point harness
Figure 26 Comparison of three point seat belt and five point harness in
a seating system and tilt-in-space wheelchair (three year old dummy)
65
Three point seat belt
Integrated five point harness
Figure 27 Comparison of three point seat belt and five point harness in
a seating system (ten year old dummy)
The use of a harness also reduced the level of rearward occupant
excursion. The rearward head excursion of the three year old dummy in
the seating system with a tilt-in-space wheelchair base was reduced by
98 percent when the harness was used in place of the seat belt. The
corresponding figure for the ten year old dummy in the seating system
with an upright base was 90 percent.
The resultant chest acceleration (3 ms exceedance) and the chest
compression of the three year old dummy in the seating system with a
tilt-in-space wheelchair base were reduced by 27 percent and 70
percent respectively when the harness was used in place of the seat
belt. The corresponding figures for the ten year old dummy in the
seating system with an upright base were 21 percent and 39 percent.
However, care must be used when drawing conclusions from the dummy
loads or head excursions for these tests, as both wheelchairs with
integrated harnesses sustained damage due to the loads placed on the
wheelchair structure by the harness system. These loads were not
present when the unmodified wheelchairs were tested, as the relevant
loads were placed through the surrogate three point restraint system.
Therefore, a certain amount of the impact energy was absorbed in
damaging the wheelchair. Whereas deforming wheelchair structures
can sometimes reduce the loads on an occupant, it is also the case that
very high loads can result when the maximum deformation occurs.
There is also a greater risk of contact with the interior of the vehicle
because occupant excursion is usually greater when a wheelchair
deforms.
66
The testing has shown that although the addition of a five point restraint
harness to a wheelchair was a very simple solution, it requires further
development. The ability of current wheelchairs to withstand the loads
induced by an integrated harness system is poor as the wheelchair
structure has not been designed for this purpose. However, if
wheelchairs were designed with an integrated harness from the outset,
and thus with a strong enough structure, the intention of the integrated
system could be achieved.
3.7
Conclusions
•
The path of the seat belt is important for the protection of the
abdomen.
•
Film analysis suggested that a child in a wheelchair might be placed
at a higher risk of receiving an abdomen injury through belt loading
than a child in a child restraint or even a vehicle seat.
•
The lap part of the belt is more likely to load the abdomen when the
wheelchair obstructed the ideal path of the belt.
•
Wheelchair manufacturers should be encouraged to manage
positively the path of the lap and diagonal parts of the seat belt.
•
Measures to manage the path of the seat belt have the potential to
reduce the risk of abdomen loading and vertical and rearward head
excursion.
•
Some positioning harnesses can complicate the fitment of a seat
belt and may result in additional loads being applied to the abdomen
if the harness buckle rests under the seat belt.
•
A wheelchair integrated restraint harness is one way to reduce the
risk of abdomen loading and to distribute the restraint forces over a
wider area.
•
A wheelchair intended for use in a vehicle would need to be
designed to accommodate an integrated restraint harness from the
outset due to the additional loads on the backrest.
•
A wheelchair fitted with an integrated harness could potentially
increase the loads on the wheelchair tie-downs and associated
anchorages.
67
•
The lap part of the seat belt is more likely to load the abdomen
when the wheelchair compresses or deforms.
•
Manufacturers who design wheelchairs for use in a vehicle should
be encouraged to design anti-submarining features into their
products.
•
A performance criterion for abdomen loading should be included in
the dynamic test for wheelchairs to encourage the development of
occupant protection solutions.
•
Some wheelchairs are unable to withstand the forces in an impact
when they are used forward facing.
•
In some cases, the maximum deformation or compression of the
wheelchair coincides with periods of increased loading in the
dummy.
•
A crash tested supportive seating system and a crash tested base
may not perform well together.
•
The head and neck of a child in a wheelchair are not protected
during the rebound phase of an impact.
•
Wheelchair headrests (where fitted) are not intended to protect the
user in a vehicle collision and are inadequate for that function.
•
A child in a wheelchair will be exposed to a higher risk of head
contact with the vehicle structure behind their seating position than
a child in a child restraint or a vehicle seat.
•
A child in a wheelchair might be exposed to a higher risk of
receiving a soft tissue neck injury (due to the motion of their head
relative to their torso) than a child in a child restraint or a vehicle
seat.
•
A head and back restraint would reduce the risk of head contact or
soft tissue neck injury.
•
A head and back restraint within the vehicle would be appropriate
for some wheelchairs; however, it would be difficult to accommodate
wheelchairs fitted with positioning headrests with a vehicle based
68
solution. Instead, these wheelchairs would benefit from a
wheelchair integrated solution.
69
4 M1 and M2 rear facing
4.1
Field study
No M2 vehicles were found in which a wheelchair user regularly travels
rear facing. The vehicles examined in the field study were all M1
vehicles that were either purpose built or specially adapted to function as
a taxi. In each vehicle, the wheelchair user travels rear facing against
the bulkhead that separates the driver and passenger compartments.
During the study, dummies representing children aged three, six and ten
years old were seated and restrained in a range of wheelchairs. An
overview of the methods was given in Section 2.2 and the results of the
study are described in detail in Appendix B.
The study highlighted three main areas of concern: the protection that a
child’s head and neck would receive during a collision, the protection
that a child’s torso would receive during a secondary collision with the
taxi bulkhead and the geometry of the occupant restraint system.
None of the vehicles examined in the field study provided a head and
back restraint. In one vehicle, an 80 mm thick foam head support was
attached to the clear centre division, but it was unlikely to afford any
protection in a crash. When the dummy was seated in a wheelchair, the
head was adjacent to a range of surfaces and structures. The distance
between the head and these surfaces varied quite markedly in each
vehicle and for each wheelchair. It seemed likely that a child’s head
would strike one of these surfaces during a collision, which could result
in serious head and neck injuries. It was also likely that the neck would
bend significantly, possibly leading to extension injury to the cervical
spine.
The wheelchair push handles or rear wheels prevented contact between
the rear of the wheelchair backrest and the taxi bulkhead. The width of
the gap between the backrest and the bulkhead depended on the
vehicle and the type of wheelchair. It seemed likely that the wheelchair
backrest would fail if it was unsupported or the wheelchair would rotate
about the rear wheels. In either event, the child would be thrown against
the bulkhead with considerable force, which could result in multiple
injuries.
When a wheelchair user is travelling rear facing, the main function of the
occupant restraint is to prevent them from riding up the back of the
wheelchair and to hold them in place during rebound. Although the
70
effects of poor seat belt geometry may be less significant for rear facing
children compared with forward facing children, it might lead to greater
vertical excursion and less favourable belt paths. A child would
therefore be at greater risk of head and neck injury due to head contact
and at greater risk of soft tissue injuries from the seat belt.
4.2
Scope of testing
The aim of the test programme was to examine whether children in
wheelchairs and children in vehicle seats are likely to receive a
comparable level of protection in a collision. When children travel rear
facing, their protection is influenced mainly by their wheelchair and the
vehicle they are travelling in, but also by their restraint system.
A wheelchair takes the place of a vehicle seat when it is used in
transport. It must, therefore, be able to withstand the forces in a crash
without transferring excessive forces to the child. A rear facing front
impact test is not included in ISO 7176-19:2001, and hence the literature
that accompanies a new wheelchair usually states that it should be used
forward facing only in a vehicle. Nevertheless, wheelchair users are
asked to travel rear facing in purpose built or adapted taxis. However,
children use a range of different wheelchairs, as highlighted in Section
2.3.4, and each type of wheelchair has various features and adjustments
that could affect the risk of injury in a crash. Furthermore, most of these
wheelchairs result in there being a gap between the wheelchair and the
bulkhead. As a result, it seems unlikely that the bulkhead will afford the
necessary support to the rear of the wheelchair. It also seems unlikely
that the head and neck of the child will be supported during a collision.
With these points in mind, it was considered important for the project to
include all types of wheelchairs in common use by children. It was also
considered important to investigate the effect of the features and
adjustments that were most relevant for transport.
Assuming that the vehicle is crashworthy and there is no passenger
compartment intrusion, the layout of the interior is the main way that the
vehicle can influence the risk of injury. The environment must be
compatible with children’s needs during a collision. However, the field
study revealed that aspects of the interior might cause injury when
children travel rear facing.
The restraint system comprises a wheelchair restraint to hold the
wheelchair in place during rebound and an occupant restraint to prevent
ejection and reduce the risk of contact with the interior. It is also
important for the occupant restraint to distribute the restraint forces over
71
the strongest parts of the child’s anatomy. Although these forces may
be relatively low compared with the front impact situation, they may
nevertheless cause soft tissue injuries if the belt route is poor. The
performance of wheelchair and occupant restraints for rear facing
wheelchair users is not currently assessed dynamically. Most vehicles
are fitted with similar equipment: a two point wheelchair restraint
integrated into the bulkhead and a three point inertia reel seat belt,
which is sometimes shared with the rear facing tip-up seat.
It was not considered worthwhile to make a detailed investigation of the
restraint system issues for rear facing children in wheelchairs, since the
devices currently in use are relatively similar in design and probable
performance. Nevertheless, a very large test programme would be
required to examine every combination of wheelchair and other vehicle
issues, particularly when all the various types and adjustments are
considered. TRL and the DfT agreed a more pragmatic approach, which
was to test a series of common worst cases. This approach was used
for the wheelchair and vehicle issues.
In summary, a worst case approach was adopted when selecting the
wheelchair and vehicle issues to examine in the test programme. In
each test, the wheelchair was restrained by a two point webbing system
while the occupant was restrained by a surrogate lap and diagonal
inertia reel seat belt with an upper anchorage. The seat belt was
installed to achieve the best fit possible for the particular wheelchair.
4.3
Test design
As a starting point, the key wheelchair and vehicle design issues were
combined in order to determine which issues should be examined in
more depth. The next step was to take these issues and construct a
matrix for each type of wheelchair. Each matrix displayed all the tests
that would be required to complete the picture for the particular
wheelchair when it was used rear facing in an M1 or M2 vehicle. The
final step was to apply our expertise in impact biomechanics and our
knowledge of injury mechanisms to identify priorities within each matrix.
These priorities would be used to develop solutions for all combinations
of wheelchair type, adjustment and child occupant size, etc. The
following sections outline this process.
4.3.1 Key issues
Tables 14 to 17 each represent a type of wheelchair. The first row in
each table lists the key issues for that device when it is used rear facing
in an M1 or M2 vehicle. There were a number of different options or
72
adjustments for each issue that might affect a child’s risk of injury in a
crash. The most important issues for a particular wheelchair were
selected on the basis of their frequency and likely influence on injury. In
each table, a tick means that the issue was examined in the test
programme and a square means that the most common or worst case
was adopted during the test set up, as appropriate. A shaded cell
means that no option or adjustment was possible for that wheelchair.
Table 14 summarises the key issues for buggies when children travel
rear facing in M1 or M2 vehicles. Backrest angle, tilt angle and occupant
size were identified as having the greatest potential to affect the injury
mechanisms in a buggy and were therefore considered for the test
programme.
Buggies are not intended to be used rear facing in a vehicle and are not
tested in that condition. Nevertheless, the reality is that they will travel
that way in a purpose built or adapted taxi. It is possible that the
backrest of a buggy will collapse when loaded by a child during an
impact. However, assuming that the strength of the backrest is
sufficient, the child’s injury mechanisms could be affected by the
backrest angle. When a backrest is reclined, there is a risk that the child
would ride up the surface of the backrest, increasing vertical head
excursion and the risk of head and neck injury through head contact with
the vehicle interior. When a backrest is upright, a child is less likely to
ride up the backrest, but there is a risk of neck injury due to
overextension. Some buggies provide a headrest or a backrest tall
enough to support the head; however, this would not have been
designed or tested as a head restraint for a rear facing system. When
the seat and backrest are fixed but tilted rearwards, there is also a risk
that the child would ride up the surface of the backrest. Occupant size
was included because the size of the child affects the way they load the
wheelchair backrest and also their sitting height with respect to the
bulkhead.
Most children using a buggy will have a positioning harness. This type
of harness is not usually crash tested and is not, therefore, intended to
take the place of a seat belt. It is possible that the harness might
interfere with the path of the seat belt during a crash. An investigation of
different harness designs and their potential to affect the performance of
the seat belt was not carried out. Instead, a typical positioning harness
was fitted in all tests with a buggy.
Buggies can be found with a range of different push handle styles and
some can be deployed or folded away. The style and position of the
73
push handles would affect the way the buggy interacts with the vehicle;
however, a large number of tests would be required to investigate each
combination. Buggies with fairly typical push handles were used in the
test programme and they were adjusted to reflect the most likely
scenario of use.
The seat is usually forward facing in a buggy, but some models have
rear facing seats while others have dual facing seats. Although the
effect of the seat orientation could be significant, only a few products
display this feature and it seemed likely that most buggies would be
used with the seat installed forward facing. Seat orientation was not,
therefore, investigated in the test programme.
Table 14 Buggies – key issues
Seating
type
Backrest Tilt
Postural Push
Seat
Occupant
angle
angle belts
handles direction size
Basic
9
9
9
Supportive
9
9
9
Table 15 describes the key issues for manual wheelchairs when children
travel rear facing in M1 or M2 vehicles. Backrest angle, tilt angle and
occupant size were identified as having the greatest potential to affect
the injury mechanisms in a manual wheelchair and were therefore
considered for the test programme. As discussed above, backrest angle
can affect the likelihood of the occupant riding up the wheelchair
backrest and the likelihood of neck extension. Occupant size can affect
the wheelchair loads and the position of the head with respect to the
bulkhead.
Although tilt angle may affect the way the child rides up the wheelchair
backrest, manual wheelchairs with a tilt-in-space facility (i.e. comfort
wheelchairs) are not used widely by children. This issue was not
investigated in the test programme.
Most manual wheelchairs are fitted with side guards to protect the child’s
clothes from spray from the wheelchair wheels. Although they perform
an important function, they can complicate the fitment of the occupant
restraint in a vehicle. Side guards were fitted in all tests with a manual
wheelchair to give a feel for their effect.
The style of the push handles fitted to manual wheelchairs can vary and
sometimes they are removed. Push handles would affect the way the
74
wheelchair interacts with the vehicle; however, the majority of basic
manual wheelchairs are likely to have fairly typical push handles fitted.
Active user wheelchairs are unlikely to have push handles. For these
reasons, this issue was not considered for the test programme.
Table 15 Manual wheelchairs – key issues
Frame
type
Basic
Backrest Tilt
angle
angle
Side
guards
Push
handles
Occupant
size
9
9
Active
user
9
Table 16 summarises the key issues for electric wheelchairs when they
travel rear facing in M1 or M2 vehicles. Backrest angle, tilt angle and
occupant size were identified as having the greatest potential to affect
the injury mechanisms in an electric wheelchair. As a result, these
issues were considered for the test programme.
Table 16 Electric wheelchairs – key issues
Backrest Tilt angle Occupant
angle
size
Electric
9
9
9
Table 17 summarises the key issues for supportive seating systems
when they travel rear facing in M1 or M2 vehicles. Moulded seating
systems were not investigated in the test programme. A child in a
moulded seat would not be accommodated easily using the restraint
system in a purpose built or adapted taxi. Furthermore, current test
dummies would not permit a full investigation of the situation. Although
a seat could be moulded to a dummy, it could not reproduce the physical
characteristics and issues associated with certain medical conditions.
As such, the restraint of a child in a moulded seat may require a
bespoke solution to meet their particular needs. However, it was
impossible to examine individual cases in the project.
Tilt angle and occupant size were identified as having the greatest
potential to affect the injury mechanisms in a modular seating system
and were therefore considered for the test programme. As discussed
above, tilt angle can affect the likelihood of the occupant riding up the
backrest and occupant size can affect the loads applied to the
wheelchair and the position of the head with respect to the bulkhead.
75
There are several different types and levels of support cushions and
pads used within supportive seating units. Although it would be
desirable to understand the effects of the different levels of support that
are available, this type of assessment was impossible within this project.
This issue was not examined in detail in the test programme, but a
modular seat was used with the full range of support equipment fitted.
Children in supportive seats are likely to use a positioning harness. As
discussed above, this harness might interfere with the path of the
occupant restraint system in the vehicle. However, this issue was not
considered for the test programme and a typical harness was used.
Table 17 Supportive seating systems – key issues
Seating
system
Modular
Tilt angle
Supports
9
Postural
belts
Occupant
size
9
Moulded
4.3.2 Final test selection
Having identified the key issues for further investigation, the next step
was to take these issues and construct a matrix for each type of
wheelchair. These are shown in Tables 18 to 21. Each matrix displays
all the tests that would be required to complete the picture for the
wheelchair when it is used rear facing in an M1 or M2 vehicle. While it
would be desirable to perform all the tests in each table, a number of
priorities were identified, which could be used to investigate the issues
and develop solutions for all combinations. A tick means that a test was
selected for the final test matrix.
Table 18 shows all the tests that would complete the picture for children
travelling rear facing in buggies in M1 or M2 vehicles. Backrest angle,
tilt angle and occupant size were identified as key issues for both types
of buggy. When the backrest is upright, the child is at risk of
overextension injury to the neck and applies greater loads to the
backrest. When it is reclined, the child is more likely to ride up the
backrest and strike their head on the vehicle interior. Buggies are
usually available with a range of seat sizes. These were compared with
the dimensions of child dummies, which revealed that the six year old
dummy matched the smallest seat size for a basic buggy while the ten
year old matched the largest seat size. Similarly, the three year old
dummy matched the smallest seat size for a supportive buggy while the
six year old matched the largest seat size.
76
If a basic buggy was used upright during a collision, a larger child would
apply greater loads to the backrest than a smaller child. It is also
possible that the head of a larger child would be more likely to be
exposed above the top of the backrest. This could result in head injury
due to impact with the vehicle structure and/or neck injury due to
extension. The ‘upright’ test with the ten year old dummy was therefore
selected as a priority.
If a basic buggy was reclined during a collision, the head of a larger child
would be more likely to strike the interior of the vehicle after riding up the
backrest. The ‘reclined’ test with the ten year old dummy was therefore
selected as a priority.
A similar approach was taken for supportive buggies. If the backrest
was upright during a crash, a larger child would apply greater loads than
a smaller child and they would be more likely to strike their head. The
‘upright’ test with the six year old dummy was therefore selected as a
priority. If a backrest was reclined, the risk of head and neck injury due
to ramping would be greater for a larger child. The ‘reclined’ test with
the six year old dummy was therefore selected as a priority.
Although some buggies are available with a tilting seat, TRL concluded
that the issues around tilt-in-space could be investigated better with
another type of wheelchair. As a result, no ‘tilted’ tests were prioritised
for either type of buggy.
77
Table 18 Buggies – test selection
Seating
type
Basic
Backrest or
Dummy
tile angle
6 year old
Upright
10 year old
9
6 year old
Reclined
10 year old
9
6 year old
Tilted
10 year old
3 year old
Upright
Supportive
Priorities
6 year old
9
3 year old
Reclined
6 year old
9
3 year old
Tilted
6 year old
Table 19 shows all the tests that would complete the picture for children
travelling rear facing in manual wheelchairs in M1 or M2 vehicles.
Backrest angle and occupant size were identified as key issues for
manual wheelchairs. Basic manual wheelchairs are available with an
upright or a reclined backrest, but active user wheelchairs have a small
upright backrest only.
Both types are usually available with different seating dimensions and
active user wheelchairs can sometimes be adjusted. The smallest seat
in a typical basic wheelchair with an upright backrest would
accommodate a child similar in size to a three year old dummy. The
largest seat would accommodate a child similar in size to a ten year old
dummy. The smallest seat in a typical basic wheelchair with a reclining
backrest would accommodate a child similar in size to a six year old
dummy and the largest seat would accommodate a child similar to a ten
year old dummy. The corresponding dummies for a typical active user
wheelchair are a six year old and a ten year old.
Children travelling in a basic manual wheelchair with an upright backrest
are at risk of head and neck injury due to head contact with the interior.
They are also at risk of extension injury to the neck with or without head
78
contact. Furthermore, the wheelchair backrest might fail, which could
result in multiple injuries if the child is thrown against the vehicle
bulkhead. Very young children have a lower injury tolerance; however,
older children apply greater loads to the backrest. In this instance, both
the smallest and largest children needed to be considered because they
were very different in terms of their level of development and could have
different injury mechanisms. The three year old dummy and the ten year
old dummy were therefore selected as priorities for basic manual
wheelchairs with an upright backrest.
If a basic manual wheelchair with a reclined backrest was used in a
crash, it is likely that the child would ride up the backrest and strike their
head on the bulkhead. Taking into account the prevalence of reclining
wheelchairs for children, it was concluded that the risks associated with
travelling in this way would be examined with other wheelchair types.
The low backrest in active user wheelchairs places an additional risk on
the back and spine due to the lack of support above the thoraco-lumbar
region. The risk of injury is similar irrespective of occupant size;
however, a larger child would apply greater loads to the wheelchair.
The test with the ten year old dummy was therefore selected as a
priority.
Table 19 Manual wheelchairs – test selection
Frame type
Backrest
angle
Dummy
3 year old
Upright
Basic
Active user
Upright
9
6 year old
10 year old
Reclined
Priorities
9
6 year old
10 year old
6 year old
10 year old
9
Table 20 shows all the tests that would complete the picture for children
travelling rear facing in electric wheelchairs in M1 or M2 vehicles.
Backrest angle, tilt angle and occupant size were identified as key
issues for electric wheelchairs. Based on the dimensions of the seat,
electric wheelchairs are used by children that range in size between the
six year old and ten year old child dummies.
79
During a collision, a child travelling in an electric wheelchair with an
upright backrest would be at risk of head and neck injury from head
contact and neck injury from extension. It is also possible that the
wheelchair backrest might fail, which could result in multiple injuries if
the child is thrown against the vehicle bulkhead. Younger children would
be most at risk from the added danger of wheelchair movement, while
older children apply greater loads to their backrest and may find their
head closer to the vehicle interior. The level or risk meant that it was
necessary to consider both the youngest and oldest children. The six
year old dummy and the ten year old dummy were therefore selected as
priorities for electric wheelchairs with an upright backrest. Taking their
prevalence for children into account, it was decided not to include
electric wheelchairs with a reclining backrest or a tilt-in-space facility.
Table 20 Electric wheelchairs – test selection
Backrest or
tilt angle
Upright
Electric
Reclined
Tilted
Dummy
Priorities
6 year old
9
10 year old
9
6 year old
10 year old
6 year old
10 year old
Table 21 shows all the tests that would complete the picture for children
travelling rear facing in supportive seating systems in M1 or M2 vehicles.
Tilt angle and occupant size were identified as the key issues for
supportive seats. Based on the dimensions of the seat, these are used
by children that correspond in size with a range of child dummies from
the three year old up to the ten year old.
If a supportive seating system was used with an upright backrest during
a collision, a child would risk head and neck injury due to head contact
and neck injury due to extension. It is also possible that the backrest
might fail, which could result in multiple injuries if the child is thrown
against the vehicle bulkhead.
Younger children have a lower injury tolerance than older children;
however, older children apply greater loads to the backrest and their
head is more likely to be closer to the interior surfaces of the vehicle. In
this instance, both the smallest and largest children needed to be
80
considered because they are very different in terms of their level of
development and have different injury mechanisms. The three year old
dummy and the ten year old dummy were therefore selected as priorities
to examine the possible injury mechanisms for children in supportive
seating units with an upright backrest.
If a supportive seating system was used with a tilt-in-space wheelchair
base during a collision, a child would be at risk of riding up the backrest
and striking their head on the vehicle interior. The largest tilt angle
represents the greatest risk. When the wheelchair is used in this way,
children travelling rear facing in an M1 or M2 vehicle could be at a
significant risk of injury. Their head would be positioned very close to
the bulkhead and the potential for ramping up would be great. The
perceived level of risk necessitated tests with both dummy sizes. The
three year old and the ten year old dummies in a fully tilted wheelchair
were therefore selected as priorities for seating units with a tilt-in-space
base.
Table 21 Supportive seating systems – test selection
Seating
system
Tilt angle
Dummy
3 year old
Upright
Priorities
9
6 year old
Modular
Tilted
10 year old
9
3 year old
9
6 year old
10 year old
9
4.3.3 Test matrix
The final step was to compile the tests identified as priorities from Tables
18 to 21. These are shown in Table 22, along with three baseline tests
with the dummies restrained in a typical vehicle based restraint system.
This vehicle scenario was intended to represent purpose built or adapted
taxis where wheelchair users travel rear facing against the bulkhead that
separates the driver and passenger compartments. Whereas a full body
shell would represent the complex interaction between the wheelchair,
the occupant and the bulkhead, it was important to represent the range
of different vehicle makes and models. It was felt that a generic mock
up would provide information that could lead to more robust
recommendations for this vehicle type. A mock up was created to
81
reproduce the essential interactions without being linked to a specific
vehicle.
Table 22 Test matrix – M1 or M2 rear facing
Wheelchair
Buggy – basic
Buggy – supportive
Backrest or
tilt angle
Upright
Reclined
Upright
Reclined
Manual – basic
Upright
Manual – active user
Upright
Electric
Upright
Supportive seating system –
modular
Upright
Tilted
Vehicle seat
Dummy
10 year old
10 year old
6 year old
6 year old
3 year old
10 year old
10 year old
6 year old
10 year old
3 year old
10 year old
3 year old
10 year old
3 year old
6 year old
10 year old
4.3.4 Test set up
Figure 28 shows the set up in typical tests with rear facing wheelchairs.
The image on the left shows a baseline test with the ten year old
dummy, while the image on the right shows a corresponding wheelchair
test. A two point webbing restraint was used to restrain the wheelchair
in rebound and a three point seat belt held the dummy in place.
The wheelchairs were restrained by the two rear straps from a
production model four point webbing system that was secured to the
floor by aluminium track fittings. The wheelchair restraints were not
designed for use in this orientation. However, it was considered that the
loads in the restraints during the later phase of the impact, when the
wheelchair moves away from the bulkhead, would be much lower than
the loads that the restraints were designed and tested to withstand.
The dummy was restrained independently by a three point seat belt.
The seat belt included an inertia reel and an upper anchorage point on
the B pillar. The seat belt was a surrogate model developed for the test
programme by a manufacturer of commercial wheelchair tie-downs and
82
occupant restraint systems through consultation with another wheelchair
and occupant restraint manufacturer. The performance of the surrogate
seat belt was verified with the four point webbing restraint during a
dynamic test according to ISO 10542-1:2001.
All test pieces were installed according to the manufacturer’s instructions
and to the ISO Standards, unless there was a strong reason for not
doing so. Any deviations from the Standards were documented. In
particular, the occupant restraint was installed to achieve the best
possible belt path for the child dummy, although it was recognised that
this was not always the case in the real world. However, it was not
within the scope of the project to investigate potentially unfavourable belt
routes and misuse.
The main aim of the tests was to investigate occupant loading in a range
of common children’s wheelchairs and compare these loads with a
vehicle seated baseline.
Figure 28 Rear facing ten year old dummy restrained in a vehicle seat
(left) and a basic manual wheelchair (right)
83
4.4
Findings
4.4.1 Relative safety of current situation
The test programme highlighted a number of issues for children
travelling rear facing in a wheelchair in an M1 or an M2 vehicle. These
issues related to the stiffness of the wheelchair and to the environment
within the vehicle.
The stiffness of the wheelchair affected its capacity to withstand the
forces of the impact. When the wheelchair deformed excessively, the
rear of the backrest struck the vehicle bulkhead and the dummy tended
to record high chest acceleration. It seemed likely that a real child would
be at risk of serious injury in these circumstances. When the dummy
was seated on the rear facing vehicle seat, the impact forces were
applied very early in the impact and over a wide area. As a result, the
chest acceleration tended to be lower than the wheelchair tests and
within the limit in FMVSS 213.
The environment within the vehicle did not afford any protection of the
head and neck (of the dummy in a wheelchair) during the impact and did
not protect the chest during secondary impact with the bulkhead. For
instance, the dummy head extended rearwards and struck the bulkhead
or the clear plastic division. Head and neck loads were high when this
occurred, although the neck bending occurred below the level of the
instrumentation. A child would be at risk of serious head and neck
injuries in these circumstances. A similar issue was observed with the
rear facing vehicle seat; however, the head tended to be closer to the
bulkhead or plastic division. This seemed to mitigate some of the loads
in certain circumstances. A secondary impact with the bulkhead
occurred when the wheelchair rotated or deformed. This usually
resulted in high chest accelerations in the dummy and hence an
increased risk of injury for a child. A child in a vehicle seat would not be
exposed to this risk, because they would be supported by their backrest
during the collision.
The following sections examine the effects of wheelchair stiffness and of
head and back restraint in more depth.
4.4.2 Effect of wheelchair stiffness
ISO 7176-19:2001 does not include a rear facing front impact test.
Since wheelchairs are not usually tested in that condition, most
manufacturers will say that their wheelchair should be used forward
facing only. It was not surprising, therefore, that wheelchair stiffness
84
varied significantly during the test programme and some wheelchairs
were unable to withstand the impact forces. An example with the three
year old dummy is shown in Figure 29. The image on the left shows the
dummy and the wheelchair just before the impact and the image on the
right illustrates how wheelchair deformation can result in additional
loading to the child. The wheelchair was a common supportive seating
system with a base supplied by a different manufacturer. The seating
attachments withstood the impact, but the base compressed and the
rear of the backrest struck the bulkhead. The chest acceleration
exceeded the baseline test by 184 percent and exceeded the limit in
FMVSS 213 by 164 percent.
Figure 29 Wheelchair stiffness in selected tests with three year old
dummy
An example with the ten year old dummy is shown in Figure 30. Once
again, the image on the left shows the dummy and the wheelchair just
before the impact and the image on the right shows the wheelchair
deformation. The wheelchair was a basic buggy. The frame of the
buggy failed during the impact and the rear of the backrest struck the
bulkhead. The chest acceleration exceeded the baseline test by 27
percent and exceeded the limit proposed by the NHTSA by 32 percent.
85
Figure 30 Wheelchair stiffness in selected tests with ten year old dummy
These two examples were selected to illustrate the importance of
wheelchair stiffness, but the same outcome was observed in all tests
with buggies (basic and supportive). In fact, wheelchairs tended to
deform in this way when the push handles were pressed against the
bulkhead, thereby preventing rotation about the rear wheels. It seems
likely that other wheelchairs that are similar in design will also be unable
to withstand the forces in a front impact crash when they are used rear
facing in a vehicle.
4.4.3 Effect of head and back restraint
Current vehicles in which a wheelchair user travels rear facing do not
provide a head and back restraint. The test programme examined the
implications for children when their head and neck are not protected
during a collision.
Figure 31 shows an example with the three year old dummy. The image
on the left shows the baseline test with the dummy seated on the vehicle
seat. The image on the right shows the dummy seated in a basic
manual wheelchair. The vehicle seat included a backrest but there was
no head restraint. During the impact, the head of the dummy struck the
bulkhead, as shown in the figure. When the dummy was seated in the
manual wheelchair, the wheelchair rotated about the rear wheels. The
backrest made contact with the bulkhead and the head of the dummy
extended rearwards until it struck the top of the bulkhead, in a similar
place as the vehicle seated test. In the case of the manual wheelchair,
the sled had come to rest when head contact occurred. As a result, very
high head acceleration and HIC were recorded. The HIC value
exceeded the vehicle seat test by 212 percent and the limit used in
86
FMVSS 213 by 124 percent. Neck loads also tended to be greater than
the baseline test.
Figure 31 Neck extension in selected tests with three year old dummy
An example with the six year old dummy is shown in Figure 32. The
image on the left shows the baseline test with the dummy seated on the
vehicle seat. The image on the right shows the dummy seated in an
electric wheelchair. When the dummy was seated on the vehicle seat,
the head struck the clear plastic division above the bulkhead before any
significant neck extension. When the dummy was seated in the electric
wheelchair, the push handles displaced the clear plastic division and
hence the neck was able to extend. As a result, very high bending
moments in extension were recorded in the neck. The extension
moment exceeded the vehicle seat test by 780 percent and the limit
proposed by Mertz et al. (2003) by 193 percent.
Figure 32 Neck extension in selected tests with six year old dummy
Figure 33 shows an example with the ten year old dummy. The image
on the left shows the baseline test with the dummy seated on the vehicle
seat. The image on the right shows the dummy seated in a supportive
87
seating unit. When the dummy was seated on the vehicle seat, the head
struck the clear plastic division above the bulkhead and displaced it from
its mounting attachments. This allowed some bending of the neck to
occur, although the head was supported to some extent by the displaced
plastic surface.
When the dummy was seated in the supportive seating unit, the push
handles displaced the clear plastic division to a much greater extent. As
a result, the neck was able to extend significantly despite the presence
of a headrest on the seating unit. The dummy recorded high bending
moments in extension in the neck. The extension moment exceeded the
vehicle seat test by 21 percent but it did not exceed the limit proposed
by Mertz et al. (2003). In general, the dummy loads in this test were not
as high as the kinematics suggested, which may have been a function of
the location of the instrumentation.
Figure 33 Neck extension in selected tests with ten year old dummy
A few examples were presented here, but the protection of the head and
neck was an important issue when the dummy was seated in every type
of wheelchair that was used in the test programme. The headrests
provided on some wheelchairs were not intended to be vehicle head
restraints and were inadequate for that purpose in these tests.
The test programme also examined the implications for children when
their chest is not protected during a secondary impact with the vehicle
bulkhead. This issue is illustrated in Figure 34 with the ten year old
dummy. The image on the left shows the dummy and the wheelchair
just before the impact and the image on the right shows the wheelchair
in contact with the bulkhead. The wheelchair was a basic manual
wheelchair. Before the impact, there was a gap between the wheelchair
backrest caused by the rear wheels and push handles. However, during
the impact, the wheelchair rotated about the rear wheels and the
88
backrest struck the bulkhead. This secondary impact occurred when the
sled had come to rest; hence the loads on the dummy were high. The
chest acceleration was 85 percent higher than the baseline test and 92
percent higher than the limit proposed by the NHTSA.
Figure 34 Chest loading in selected tests with ten year old dummy
A secondary impact with the bulkhead can occur when the wheelchair
rotates or when the wheelchair fails as shown in Section 4.4.2.
Wheelchair rotation could be prevented by an additional wheelchair
restraint, but that would increase the loads on the wheelchair backrest
and occupant neck extension. The effects of the secondary impact
could be mitigated by specifying performance requirements for the
bulkhead surfaces.
A vehicle based head and back restraint compatible with children’s
wheelchairs would address the protection of the head and neck during
the impact and the protection of the chest from secondary impacts within
the vehicle. While this would be a relatively straightforward solution for
manual and electric wheelchairs, the design of buggies and supportive
seating systems would be difficult to accommodate with a vehicle based
solution. For these devices, it may be necessary for the wheelchair to
protect these body regions.
The results of this study will have been influenced by the surface
characteristics and dimensions of the vehicle mock up and by the way
the clear plastic division was attached. However, every effort was made
to ensure that these aspects of the bulkhead were representative of real
vehicles. It follows, therefore, that the issues highlighted by the test
programme would also apply to the real world.
89
4.5
Conclusions
•
Some wheelchairs were unable to withstand the forces in an impact
when they were used rear facing.
•
When a wheelchair deformed or failed, the dummy struck the
vehicle bulkhead after it had come to rest. This resulted in high
accelerations and forces, which suggested that a child would be at
risk of injury.
•
A rear facing front impact test would address the wheelchair
strength issues.
•
The head and neck of the dummy were not protected by the vehicle
or by the wheelchair. The head struck the bulkhead or the clear
plastic division and the neck extended rearwards. A child would be
at risk of head and neck injuries in these circumstances.
•
Wheelchair headrests are not intended to protect the user in a
collision and were inadequate for that function.
•
The chest of the dummy was not protected during secondary
impacts with the bulkhead.
•
A head and back restraint would address the protection of the
child’s head and neck and would prevent secondary impacts with
the bulkhead.
90
5 M3 forward facing
5.1
Field study
The field study included M3 vehicles in which a passenger in a
wheelchair travels forward facing. In each vehicle, dummies
representing children aged three, six and ten years old were seated and
restrained in a range of wheelchairs. An overview of the methods was
given in Section 2.2 and the results of the study were described in detail
in Appendix B.
The study highlighted that the wheelchair space in an M3 vehicle is likely
to be similar to that in other M category vehicles when the wheelchair is
forward facing. As a result, the main observations for M1 and M2
vehicles with forward facing wheelchairs (summarised in Section 3.1)
also applied to M3 vehicles. Although an M3 vehicle would experience a
lower deceleration during a collision, the geometry of the occupant
restraint system, the protection of the child’s head and neck during
rebound and the amount of clear space around the child remain
important. This is because vulnerable parts of a child’s anatomy are
affected.
The occupant restraint system was installed according to ISO
10542-1:2001 and to achieve the best fit. The vehicles examined did not
provide an upper anchorage point for the occupant restraint. The lap
belt anchorages and consequently the seat belt buckle were attached to
floor tracking behind the wheelchair. This meant that the diagonal part
of the seat belt passed around the ribs before joining the lap belt at the
buckle. In some cases, the wheelchair obstructed the ideal path of the
lap part of the seat belt. These obstructions were caused by side guards
to prevent splash from the wheelchair wheels and by hip support pads to
position the child’s pelvis within the wheelchair.
The vehicles did not provide a head and back restraint for the wheelchair
user. Although there is no requirement to fit a head and back restraint,
some coaches on scheduled interurban services are equipped with
them. The vehicles examined in the field study therefore represent the
worst case. In a collision, a child’s neck would extend rearwards during
the rebound phase. This would increase the risk of head contact behind
the seating position and could lead to soft tissue neck injuries. This was
thought to represent a greater risk of injury to a child than positioning
their wheelchair with a gap between their backrest and the head and
back restraint.
91
The amount of space in front of the wheelchair user was also important,
although the current requirements would seem to be adequate to reduce
the risk of head contact for children.
5.2
Approach
The field study highlighted some similarities with other M category
vehicles that carry wheelchair users forward facing. As a consequence,
the main observations were the same for M3 vehicles as they were for
M1 and M2 vehicles. The study revealed that vulnerable parts of a
child’s body were affected, such as the head, neck or abdomen. These
body regions can be injured with relatively low rates of loading, due to
the way the human body develops through childhood. Nevertheless, the
risk of injury is likely to be lower in an M3 vehicle compared with an M1
or M2 vehicle. This was the case for adults in a previous research
project for the DfT (UG327).
During the course of the project, it became clear that there were a
number of important issues to consider for children in wheelchairs. A
comprehensive investigation of all the issues for every vehicle category
and wheelchair direction would require a very high number of sled tests.
Since M1 and M2 vehicles represented the main priority in terms of the
risk of injury to children, the DfT agreed that M3 vehicles with forward
facing wheelchairs would not be included in the test programme.
However, given the similarities mentioned above, it was anticipated that
conclusions and recommendations could be made for M3 vehicles with
forward facing wheelchairs based on the results of the sled tests
representing M1 and M2 vehicles with forward facing wheelchairs.
5.3
Conclusions
•
The path of the seat belt could be improved for children in
wheelchairs.
•
Although the vehicle deceleration pulse would be relatively low in an
M3 vehicle, a child in a wheelchair might be placed at a higher risk
of receiving an abdomen injury through belt loading than a child in a
vehicle seat.
•
The greatest improvements would be made if wheelchair
manufacturers were encouraged to manage positively the path of
the seat belt.
92
•
It is likely that children’s wheelchairs will be able to withstand the
forces in a collision when they are used forward facing in an M3
vehicle.
•
The head and neck of a child are unlikely to be protected during the
rebound phase of a front impact.
•
A child in a wheelchair should be provided with a head and back
restraint if it is intended that they should receive a level of protection
that is comparable to that for a child travelling in a vehicle seat.
•
A head and back restraint within the vehicle would be appropriate
for some wheelchairs; however, it would be difficult to accommodate
wheelchairs fitted with positioning headrests with a vehicle based
solution. Instead, these wheelchairs would benefit from a
wheelchair integrated solution.
93
6 M3 rear facing
6.1
Field study
The field study included M3 vehicles in which a passenger in a
wheelchair travels rear facing (i.e. usually low floor buses). In each
vehicle, dummies representing children aged three, six and ten years old
were seated in a range of wheelchairs. The wheelchairs were
positioned in the wheelchair space, which is a protected area fitted with
a padded backrest. An overview of the methods was given in Section
2.2 and the results of the study are described in detail in Appendix B.
In this section, any references to locations or directions within the
wheelchair space are made with respect to the bus. For example, the
front end of the wheelchair space is towards the front end of the bus and
the rear end of the space is towards the rear of the bus. However, any
references to locations or directions on the wheelchair are made with
respect to the wheelchair, irrespective of the direction that it faces.
The study highlighted some potential issues of compatibility between
children’s wheelchairs and the padded backrest in low floor buses. For
example, the backrest was wider than the distance between the handles
on the manual wheelchair used in the study. This meant that the
handles were unable to pass either side of the backrest. Instead, they
rested against the padded surface, resulting in a gap between the
backrest and the dummy. The head of a child travelling in this way
would extend rearwards (i.e. towards the front of the bus) in the event of
heavy braking or a collision. This motion might result in a soft tissue
neck injury. It was also noted that the wheelchair was not as far
forwards in the wheelchair space when the handles rested against the
backrest. This meant that the wheelchair was positioned differently with
respect to the vertical stanchion or the retractable rail than it would have
been if the handles passed either side of the backrest. This might
increase the risk of the wheelchair moving sideways into the gangway
during normal driving manoeuvres. This will be examined in Section 7.
The Public Service Vehicles Accessibility Regulations 2000 (SI 2000 No.
1970; as amended) include dimensions for a backrest to be fitted when
wheelchair users travel rear facing. The width of the backrest must fall
between 270 mm and 300 mm at a height exceeding 830 mm from the
floor. Below this height, the width of the backrest must fall between
270 mm and 420 mm. The DfT commissioned a survey of occupied
wheelchairs and scooters to determine their overall mass and
94
dimensions. The findings of the survey were reported by Hitchcock et al.
(2006). The average distance between the handles of the children’s
wheelchairs in the survey was 292 mm. A child was defined as a person
under the age of 16 years and the average age of the children was ten
years.
Another compatibility issue was found when the electric wheelchair was
positioned against the padded backrest in each vehicle. The electric
wheelchair used in the study included a large base that extended
rearwards behind the wheelchair seat. This pressed against the
mounting structure below the bottom edge of the padded surface and
introduced a gap between the backrest and the dummy. Once again, a
child travelling in this way might be at risk of soft tissue neck injury in the
event of heavy braking or a collision and their wheelchair would be
positioned differently with respect to the stanchion or rail.
Hitchcock et al. (2006) assessed whether the wheelchairs in their survey
would be likely to fit against the backrest defined in the Regulations.
This revealed that 71 percent of the electric wheelchairs used by
children would not fit. The reasons included the handles being too close
together, a continuous bar handle preventing the backrest from locating
against the body of the wheelchair, narrow wheels and the battery or
other items obstructing the backrest. While this gives an indication of the
compatibility of children’s wheelchairs with the backrest in buses,
dimensions of the area around the base of electric wheelchairs were not
included.
In order to understand further the influence of the base or battery of
electric wheelchairs on the interaction with the backrest, Hitchcock
(2008) provided some additional measurements. These included the
distance from the rear surface of the wheelchair backrest to the rear
edge of the base and the height of the base from the floor. Of the 59
electric wheelchairs examined, 51 (86 percent) were found where the
base extended further rearwards than the rear surface of the wheelchair
backrest. The implication is that these wheelchairs might not fit against
the backrest. The measurements are summarised in Table 23.
In addition, Hitchcock (2008) provided similar measurements for manual
wheelchairs. The manual wheelchair used in the field study was
incompatible with the backrest because the push handles were too
narrow to pass by the sides. Other manual wheelchairs may have push
handles that are further apart, but instead, the anti-tip devices may
prevent the wheelchair from achieving the correct position against the
backrest. The measurements provided by Hitchcock included the
95
distance from the rear surface of the wheelchair backrest to the rear
edge of the anti-tip devices and the height of the anti-tip devices from
the floor. Of the 151 manual wheelchairs examined, 125 (83 percent)
were found with anti-tip devices that extended further rearwards than the
rear surface of the wheelchair backrest. The data from these
wheelchairs are summarised in Table 24.
Table 23 Electric wheelchair measurements (Hitchcock, 2008)
Measurement
Backrest to base
Height of base
Function
Mean
95th percentile
50th percentile
5th percentile
Mean
95th percentile
50th percentile
5th percentile
Value (mm)
111
263
102
7
365
449
369
293
Table 24 Manual wheelchair measurements (Hitchcock, 2008)
Measurement
Backrest to anti-tip
devices
Height of anti-tip
devices
6.2
Function
Mean
95th percentile
50th percentile
5th percentile
Mean
95th percentile
50th percentile
5th percentile
Value (mm)
112
216
115
15
263
426
261
125
Approach
The field study raised some questions about the interaction between
children’s wheelchairs and the equipment in the wheelchair space in low
floor buses. A backrest is required to support the back of the wheelchair
(and the user) and to prevent the wheelchair from tipping rearwards
when the vehicle is in motion. A means of restricting movement of the
wheelchair into the gangway is required to maintain the wheelchair
within the wheelchair space. It is likely that this equipment will afford a
degree of protection in the event of a collision as well as in normal
driving manoeuvres.
96
Other vehicle occupants, and in particular standing passengers, are
afforded little protection in the event of a collision. The Public Service
Vehicles Accessibility Regulations 2000 (SI 2000 No. 1970; as
amended) specify requirements for the strength of the backrest,
although this may only address loads in normal travel. The
management of the occupant’s loads is not considered for vehicle
seated passengers or for wheelchair seated passengers. It could be
argued, therefore, that a comparable level of protection is afforded.
Nevertheless, children in wheelchairs may be more vulnerable,
particularly due to the issues highlighted in the field study.
During the course of the project, it became clear that there were a
number of important issues to consider for children in wheelchairs. A
comprehensive investigation of all the issues for every vehicle category
and wheelchair direction would require a very high number of sled tests.
Since M1 and M2 vehicles represented the main priority in terms of the
risk of injury to children, the DfT agreed that M3 vehicles with rearward
facing wheelchairs would not be included in the test programme.
However, it was anticipated that conclusions and recommendations
could be made for M3 vehicles with rearward facing wheelchairs based
on the results of the field study. Furthermore, a study was carried out to
examine whether the backrest or methods for restricting lateral
movement of wheelchairs described in the Regulations are adequate for
children’s wheelchairs. This study will be reported in Section 7.
6.3
Conclusions
•
M3 vehicles in which a passenger in a wheelchair travels rear facing
(i.e. low floor buses) also carry standing passengers and do not,
therefore, offer crash protection above that provided by the vehicle
structure.
•
Although it is not its intended function, the backrest that supports
the wheelchair user, and the stanchion or other means of restricting
movement into the gangway, are likely to provide a degree of
protection for a child in the event of a collision.
•
The gap between the handles of some children’s wheelchairs is
likely to be too small for the handles to pass on either side of the
backrest.
•
The base of some electric wheelchairs might extend further
rearwards than the space below the backrest in vehicles.
97
•
A gap between a child in a wheelchair and a backrest in the vehicle
might result in the child being placed at an increased risk of soft
tissue neck injury.
98
7 M3 non-impact protection
7.1 Scope
The requirements of the Public Service Vehicles Accessibility
Regulations 2000 (SI 2000 No. 1970; as amended), being the relevant
legislation in the UK, are the focus for this section; however, it is
recognised that requirements for M3 vehicles are also made in
European Commission Directive 2001/85/EC and in UNECE
Regulation 107 and that these requirements may differ slightly from the
UK Regulations.
The Public Service Vehicles Accessibility Regulations 2000 (SI 2000 No.
1970; as amended) allow a wheelchair user in a bus to travel facing
rearwards, in a protected area fitted with a backrest. Earlier research
carried out by TRL demonstrated that this configuration will prevent an
adult in a wheelchair from tipping during normal transit (Le Claire et al.,
2003).
The Regulations also demand a method for restricting lateral movement
of the wheelchair into a gangway. This lateral restraint can be a vertical
stanchion situated at the front end of the wheelchair space and running
continuously from the floor to the roof, or a retractable horizontal rail
extending from the front of the wheelchair space. A range of positions
for both these items within the wheelchair space is specified. Figure 35
summarises the requirements for the wheelchair space in buses.
Previous research carried out for the DfT by TRL (UG327) examined the
extent of lateral movement of an adult wheelchair during normal driving
conditions in a bus that was compliant with the Regulations. A 50th
percentile male Hybrid II dummy was seated in the Disability
Discrimination Act Reference Wheelchair, while a bus was driven
through a manoeuvre that generated levels of lateral movement
recorded on real bus routes. Wheelchair displacement was observed,
but it was restricted by the vertical stanchion on the edge of the
wheelchair space. Performance of the horizontal rail was dependent on
height, as it restricted lateral movement of the wheelchair at lower
positions but did not at higher positions that were allowable within the
Regulations.
Children’s wheelchairs are narrower than those for adults and some
have pushchair style handles. It was not clear whether the backrest or
the methods for restricting lateral movement (namely the vertical
99
100mm
120mm
100
830mm
870mm
1300mm min
Figure 35 Wheelchair space in buses
400mm
560mm
4 degrees min
8 degrees max
Backrest
300mm max
1000mm min
540mm
560mm
Padded surface
must pass
through this
area
To the point
where there is
at least 45mm
clearance
Vertical stanchion
Handrail
750mm min
900mm max
270mm
420mm
270mm
300mm
90mm
max
stanchion or horizontal rail) that are described in the Regulations are
adequate to restrict movement of children’s wheelchairs.
830mm max
1000mm max
850mm min
775mm max
350mm
480mm
The main objective of the work reported here was to investigate
paediatric wheelchair displacement during normal driving conditions in a
bus that is compliant with the Regulations. A series of trials was
undertaken to repeat the adult study described above, this time using
children’s wheelchairs and child dummies. A number of combinations of
wheelchairs and child dummy sizes were used in order to check the
effect of different styles of child wheelchair and occupant size and
weight.
7.2 Testing methodology
Previous research at TRL has demonstrated that lateral accelerations on
low floor buses can reach 0.4 g on bus routes selected as being difficult
to negotiate (Stone, 1999; unpublished Project Report). The study using
adult wheelchairs described a test procedure to achieve this level of
lateral acceleration where a low floor bus was driven around a bend of
20 metres constant radius at a constant speed of approximately 24 mph.
The procedure was replicated for this testing (Figure 36). However, it
was found that a speed of 21 to 23 mph was sufficient to achieve the
required lateral acceleration. The speed and lateral acceleration of the
bus was measured using global positioning system technology.
40 metres
21 - 23 mph
Figure 36 Diagram showing test procedure
Two low floor buses were used for the testing, one with each type of
lateral restraint fitted. The vertical stanchion was fitted in Bus 1, and the
horizontal retractable rail was fitted in Bus 2 (Figure 37). Both buses
were in current use on scheduled services and had been certified
according to the Public Service Vehicles Accessibility Regulations 2000
(SI 2000 No. 1970; as amended).
In the remainder of this section, any references to locations or directions
within the wheelchair space are made with respect to the bus. For
example, the front end of the wheelchair space is towards the front of
the bus and the rear end of the space is towards the rear of the bus.
101
Bus 1 (vertical stanchion)
Bus 2 (retractable rail)
Figure 37 Buses used in study
Bus 1 had the wheelchair space on the right side of the bus, and
therefore was driven around the bend in a clockwise direction (right hand
turn) to ensure that the lateral acceleration on the wheelchair acted
towards the opposite side of the bus. The wheelchair space in Bus 2
was on the left side of the bus, so it was driven around the bend in an
anti-clockwise direction (left hand turn).
The cranked vertical stanchion and backrest in Bus 1 are shown in
Figure 38.
Back restraint
Cranked stanchion
Figure 38 Vertical stanchion and back restraint in Bus 1
The horizontal retractable rail in Bus 2 in both the raised and lowered
positions is shown in Figure 39.
102
Back restraint
Raised rail
Lowered rail
Figure 39 Retractable rail and backrest in Bus 2, showing rail raised
(left) and lowered for use (right)
Three different-sized child dummies and three different wheelchairs
were used in the study. The dummies used were a Q3 (three year old),
a Hybrid III six year old and a P10 (ten year old). The wheelchairs used
were a supportive buggy, an electric wheelchair and a manual
wheelchair. These wheelchairs were described in detail in Section 2.2.3.
The six year old and ten year old dummies were tested in both the
electric and manual wheelchairs, while the three year old was only
tested in the supportive buggy. The three year old dummy was seated
in the supportive buggy using the integral harness provided. The
dummies and wheelchairs are shown in Figure 40.
Three year old dummy in
supportive buggy
Six year old dummy in
electric wheelchair
Ten year old
dummy in manual
wheelchair
Figure 40 Dummies and wheelchairs used in study
The wheelchairs were positioned in the wheelchair spaces such that the
centreline of the wheelchair aligned with the centreline of the backrest.
The wheelchair was moved as far forwards in the wheelchair space as
103
possible, so that the wheelchair was in contact with the backrest. All the
wheels on the wheelchair were aligned in the fore/aft direction, with the
brakes applied where fitted. Two video cameras were mounted in the
bus to film the movement of the wheelchairs and dummies during the
test runs.
7.3 Results
Both the vertical stanchion and the horizontal retractable rail are
designed to prevent movement of a wheelchair into the gangway of a
bus, as this could be hazardous for both the wheelchair occupant and
other bus users, especially those standing in the vicinity. In this study, a
wheelchair was considered to be restrained effectively if all parts of it
remained inside the wheelchair space during the manoeuvre and the
occupant remained in the wheelchair at the end of the manoeuvre.
7.3.1 Observations before testing
A number of observations were made before testing regarding the
position of the wheelchairs within the wheelchair spaces. One of the
main observations was that there were compatibility issues between the
wheelchairs and the backrests in each bus. This is illustrated in Figure
41.
The first incompatibility issue was that the backrests on both buses were
wider than the gap between the handles on the manual wheelchair,
meaning that the wheelchair occupant was not in contact with the
backrest. This meant that there was no restraint to support the head of
the dummy, which could lead to potential injury to the neck in the event
of heavy braking or a front impact.
The second issue that was identified was an incompatibility between the
battery pack and motor on the electric wheelchair with the base of the
backrest, which also resulted in the wheelchair occupant not being in
contact with the backrest. This, again, could lead to potential neck injury
as mentioned above.
Both of the compatibility issues discussed above also meant that the
wheelchair occupant was positioned further rearwards in the wheelchair
space on the bus in relation to the lateral restraint.
104
Figure 41 Examples of compatibility between children’s wheelchairs and
the backrests in typical buses
One of the other observations was that the wheelchair space was wider
than the children’s wheelchairs, resulting in there being a gap between
the wheelchair and the vertical stanchion or horizontal rail (Figure 42).
This would potentially allow more movement of a paediatric wheelchair
in the wheelchair space before contact with the lateral restraint than an
adult wheelchair.
Figure 42 Example of the distance between a typical children’s
wheelchair and the method of restricting lateral movement in a bus
105
In the bus fitted with the retractable rail, it was observed that the rail did
not align with any of the side structures of the manual or electric
wheelchairs (with the exception of the backrest of the chair) as it was too
high. This can be seen in Figure 41, shown previously.
7.3.2 Wheelchair space fitted with stanchion
The stanchion in Bus 1 was tested at three different positions in the
fore/aft direction within the allowable range in the Regulations (400 mm
to 560 mm rearwards of the front of the wheelchair space). These were
the furthest forward position (400 mm), mid position (480 mm) and
furthest rearward position (560 mm). Each wheelchair and occupant
combination was tested with each stanchion position. The stanchion
was located 875 mm from the side of the bus in the lateral direction, and
this was kept constant for all the tests.
The stanchion did not restrain the manual wheelchair effectively when in
the 400 mm or 480 mm positions. As the bus performed the manoeuvre,
the front castor wheels on the manual wheelchair turned and the front of
the wheelchair rotated around the stanchion. This led to the ejection of
both the six year old and ten year old dummies during the test (Figure
43). The brakes on the rear wheels remained engaged during the tests,
and the rear wheels were observed to skid over the floor of the bus while
the manual wheelchair rotated, with no rolling of the rear wheels being
observed.
Figure 43 Ejection of six year old dummy from manual wheelchair after
rotation of seat around stanchion (400 mm position)
The manual wheelchair was only restrained by the stanchion in the
560 mm position as the front of the large rear wheel contacted the
stanchion as the chair rotated. This prevented the full rotation of the
chair as seen in the tests with the stanchion in the 400 mm and 480 mm
106
positions. However, the chair started to tip over sideways and the
occupant was almost ejected out of the chair sideways, but was
prevented from doing so by the stanchion.
The electric wheelchair was restrained by the stanchion in all three
stanchion positions and the occupant remained seated, although rotation
of the chair was observed before it contacted the stanchion. In the test
with the stanchion in the 400 mm position, the front wheel of the
wheelchair was outside the wheelchair space at the end of the test.
The supportive buggy was restrained by the stanchion in all stanchion
positions. The front wheel of the supportive buggy was fixed in the
fore/aft position, rather than being a rotating castor as in the manual and
electric wheelchairs. This appeared to prevent any rotation of the
supportive buggy during the manoeuvre. In the tests the supportive
buggy started to tip over sideways, but was prevented from doing so as
the side rail of the supportive buggy contacted the stanchion.
7.3.3 Wheelchair space fitted with horizontal retractable rail
The horizontal retractable rail was tested in one position, as it was not
possible to adjust the height of the rail on the bus tested. The front of
the rail was approximately 725 mm above the floor of the bus in its
deployed position. The Regulations allow a rail such as this to be in the
range of 600 mm to 800 mm above the floor of the bus. As described
previously, the rail did not align with the side structures of the manual or
electric wheelchairs as it was too high. The front of the rail was
approximately 770 mm from the side of the bus in the lateral direction.
Both the manual and electric wheelchairs rotated by 90˚ during the tests,
as there was no structure on the bus to prevent this. The chairs were
not restrained within the wheelchair space by the horizontal rail. The six
year old and ten year old dummies were either ejected from the
wheelchairs or trapped between the wheelchair and the rail (Figure 44).
107
Figure 44 Ejection and entrapment of child dummies observed in testing
with horizontal rail
In the bus tested, the horizontal rail did not lock in the deployed position,
which meant that it was able to rise up when it was contacted by the
dummy in the wheelchair. In some cases this resulted in the rail
contacting the child dummy’s chest, or even the neck as shown in Figure
45.
Figure 45 Horizontal rail rose during testing, resulting in contact with
child dummy’s chest and neck
The supportive buggy did not rotate during the testing and remained
within the wheelchair space. The supportive buggy started to tip over
sideways during the manoeuvre but was restrained by the horizontal rail.
7.4 Discussion
The results indicated that there were several issues relating to the
adequacy of the Public Service Vehicles Accessibility Regulations 2000
(SI 2000 No. 1970; as amended) with regard to the restraint of children’s
108
wheelchairs in buses. The main areas of concern were the
incompatibility between the paediatric wheelchairs and the backrest and
the potential for injury to children in wheelchairs and other bus users as
a result of ejection from the wheelchairs and/or contact with the lateral
restraint.
The incompatibility issue between the manual and electric wheelchairs
and the backrest in the buses gave cause for concern. The handles on
the manual wheelchair and the battery/motor on the electric wheelchair
prevented the wheelchair occupant from being positioned close enough
to the backrest, meaning that the wheelchair occupant’s head would not
be prevented from moving rearwards in the event of heavy braking or a
frontal impact. This has the potential to result in occupant injury due to
extension of the neck. A secondary result of this incompatibility issue is
that it may result in the wheelchair being positioned further rearwards in
the wheelchair space relative to the vertical stanchion or horizontal rail.
This may reduce the ability of the lateral restraint to keep the wheelchair
and occupant within the wheelchair space during normal driving
conditions.
There are two general options for rectifying this incompatibility issue.
The first is to change the wheelchair design and the second is to change
the design of the wheelchair space. For example, potential solutions to
the issue with incompatibility between the handles and back restraint are
making the backrest narrower or modifying the wheelchair handles.
Narrowing the backrest may lead to problems with adult wheelchair
occupants not being adequately supported, so this may not be practical.
However, modifying the handles to be slightly further apart, or perhaps
able to fold out of the way of the back restraint, may be a potential
solution. In terms of the battery and motor on the electric wheelchair, it
may be more practical to change the design of the base of the backrest
rather than the wheelchair, as changes to the wheelchair may affect its
stability, for example.
The vertical stanchion in Bus 1 was not effective in restraining the
manual wheelchair in the 400 mm or 480 mm positions. The wheelchair
was able to rotate about the base of the stanchion during the
manoeuvre, which led to the ejection of both the six year old and ten
year old dummies. The stanchion only restrained the manual wheelchair
when in the 560 mm position, the furthest rearward position in the
wheelchair space allowable in the Regulations. The vertical stanchion
did restrain the electric wheelchair in all positions, although rotation of
the chair was still observed during the manoeuvre. However, these
results do not mean that the 560 mm position is necessarily the most
109
appropriate, as it is likely to be the relative position of the wheelchair and
stanchion that is more important. In the event that the compatibility
issues between the wheelchairs and the backrest are resolved, the
wheelchairs and their occupants will be seated further towards the front
of the wheelchair space.
The performance of the retractable rail in Bus 2 gave cause for concern.
The rail did not align with any part of the side structure on the manual
and electric wheelchairs due to its height above the floor and small
contact area. If the wheelchairs rotated during the manoeuvre, the rail
would most likely directly contact the wheelchair occupant. The rail
appeared to pose an injury risk to child wheelchair occupants in the
manual and electric wheelchairs as they were often contacted directly by
the restraint and either ejected from the wheelchair or trapped between
the chair and the rail. The single rail did not have any features that
might mitigate injury in the event of direct contact between the rail and a
wheelchair occupant, such as padding. The end of the rail trapped the
dummy by the chest in some cases, and in one test the end of the rail
rose up and contacted the dummy’s neck. These appeared to be
scenarios which could be potentially injurious to a child in a wheelchair.
In previous research with a 50th percentile adult dummy seated in the
Disability Discrimination Act Reference Wheelchair, the horizontal rail
was not effective at restraining the wheelchair in positions within the
allowable height of 600 mm to 800 mm (Le Claire et al., 2003). The rail
was found to be more effective at a lower height (550 mm) where it
contacted the handrims of the wheelchair and prevented movement of
the wheelchair into the gangway. This indicated that the rail may also be
more effective at restraining children’s wheelchairs if it were positioned
at a lower height. However, the reduced width of children’s wheelchairs
compared with adult wheelchairs may mean that children’s wheelchairs
are able to rotate in the wheelchair space before contacting the rail,
even if the rail is positioned at a lower height.
The rotation of the wheelchairs in the tests appeared to be a significant
contributory factor to the overall performance during the tests, especially
in relation to ejection or entrapment of the wheelchair occupants. Both
the manual and electric wheelchairs rotated in the tests with the vertical
stanchion and the horizontal rail, and the occupants were ejected in
several of these tests. The only wheelchair that was consistently
restrained within the wheelchair space with both lateral restraints was
the supportive buggy with the three year old dummy. There was no
rotation of the supportive buggy in any of the tests performed with either
lateral restraint, and this was considered to be a significant factor in the
110
supportive buggy remaining within the wheelchair space. The
supportive buggy had a fixed front wheel that could not rotate like the
front wheels on the manual and electric wheelchairs, which appeared to
be the main factor in the prevention of rotation of the supportive buggy.
Preventing the rotation of the wheelchairs could be achieved in several
different ways. Locking the front wheels in the fore/aft direction when
the wheelchair is in a wheelchair space in a bus is a potential solution,
although it is not known how effective it would be on a manual
wheelchair with much smaller front wheels than the supportive buggy.
Alternatively, the use of an additional restraint to hold the wheelchair in
place may be effective, but this could affect the ease of use of the
vehicle and wheelchair space. Solutions such as these could be further
explored through assessment.
7.5 Conclusions
• The backrest on both buses was wider than the gap between the
handles on the manual wheelchair. This meant that the head of the
dummy was not supported by the backrest.
• The battery pack on the electric wheelchair was obstructed by the
supporting structure below the backrest in each vehicle. This meant
that the head of the dummy was not supported by the backrest.
• A gap between a child’s head and the surface of the backrest could
lead to potential injury to the neck in the event of heavy braking or a
frontal impact.
• The vertical stanchion did not restrain the manual wheelchair when it
was positioned 400 mm or 480 mm rearwards of the front of the
wheelchair space; however, the stanchion did restrain the manual
wheelchair when it was 560 mm from the front of the space.
• The retractable horizontal rail appeared to pose an injury risk to
children in wheelchairs as they could be ejected from the wheelchair
or become trapped between the wheelchair and the rail.
• The rail was too high to interact with the side structure of the manual
or electric wheelchairs. This resulted in direct contact between the
rail and the dummies when the wheelchairs moved during the driving
manoeuvre.
• The rotation of the wheelchairs in the wheelchair space during the
cornering manoeuvre appeared to be a contributory factor to the
ejection of the child dummies from the wheelchairs.
111
• The manual wheelchair rotated around the stanchion in both the
400 mm and 480 mm positions, resulting in the ejection of the child
dummies.
• Both the manual and electric wheelchairs rotated in the wheelchair
space with the retractable rail, leading to either ejection or entrapment
of the child dummies.
• The supportive buggy, which had a fixed front wheel, did not rotate in
either bus during testing and remained in the wheelchair space.
112
8 Cost analysis
8.1
Introduction
In conventional vehicle safety analyses of effectiveness, changes are
evaluated in terms of the potential injuries that they would prevent. This
provides a theoretical number of injuries saved by the safety
intervention. The DfT has derived figures in order to value the benefit to
society arising from such a reduction in injury numbers. These figures
were developed based on the ‘willingness to pay’ approach. Essentially,
this approach estimates the amount that society should be willing to pay
in order to prevent an injury. It considers both human costs, such as
pain, grief and suffering, as well as direct economic costs associated
with hospital treatment and loss in earnings. The latest versions of
these figures, for 2006, can be found in Road Casualties Great Britain
2006 (DfT, 2007). It should be noted that these figures were developed
to represent the average road traffic casualty and may not be
appropriate for use exclusively with children or wheelchair users. For
instance, the expected loss in earnings may not be accurate. However,
they should provide indicative figures against which the costs of injury
saving proposals can be evaluated.
The costs associated with design changes to wheelchairs and the
vehicles that carry them also need to be derived. The costs used here
have been developed with particular consideration of three main
categories: economic and societal costs as well as environmental
effects. The costs estimated by the authors have then been considered
alongside those produced by Le Claire et al. (2003), and moderated if it
seemed appropriate to do so.
It is very important to consider that these costs are initial estimates
made by the authors. They are based on suggested changes which
have been proposed for other similar cost analyses, but are supported
by a limited knowledge of the wheelchair manufacturing processes and
market conditions. The costs have been presented here to provoke
consideration as to whether the suggested interventions would be
beneficial from a cost perspective. As such, they should be treated with
a level of caution before they have been validated by stakeholders in the
industry.
It would be possible to increase the robustness of the cost estimates
made here, through two key steps:
113
1. Wheelchair manufacturers should be consulted on the proposed
changes to improve safety for children in wheelchairs. The
manufacturers should be able to provide more accurate estimates
of costs that they might incur.
2. The costs provided in this document should be reviewed by
stakeholders in the industry and revised based on any feedback
received.
These steps should be considered to improve the estimates of cost
made in the following sections. However, it is TRL’s experience that the
costs provided by stakeholders can vary significantly from organisation
to organisation. It would be necessary, therefore, to consult a wide range
of organisations and to review the costs that are provided. While such a
review was beyond the scope of this project, it could be important if the
proposed options are taken forwards for legislation.
It is unlikely that any of the design changes suggested in this report
would affect the environment significantly. Increases in the use of raw
materials may have an environmental impact and vehicle fuel
consumption might increase if significant weight is added to the vehicle.
However, design solutions and the use of appropriate materials could
minimise these effects.
8.2
Child wheelchair users and their involvement in collisions
The number of children in wheelchairs has now risen above 100,000
(www.wheelchairchildren.org.uk). This represents around 1.18 percent
of the UK population of children less than 12 years of age1. It would be
necessary to compare the travel patterns of children in wheelchairs with
those for other children to confirm that they make up 1.18 percent of the
child vehicle users in the UK. Unfortunately, there is insufficient
information with which to do this at present. Neither is there sufficient
information to identify the proportion of child wheelchair users that
transfer to a vehicle based restraint system when travelling. Given that
some children in wheelchairs will transfer for some journeys, it is
assumed that child wheelchair users represent 1 percent of the
exposure to the UK population of children from travel risks. It is
suggested that this assumption is revised when sufficient information
becomes available with which to do so.
1
There are an estimated 8.45 million children under 12 according to National Statistics
(2007).
114
Road Casualties Great Britain 2006 (DfT, 2007) presents statistics about
personal injury road accidents and their casualties. Detailed tables are
included that cover a range of variables. One such table displays
casualties by age band, road user type and severity2. Two of the road
user type groups in the table are relevant for this research: the car
passengers group and the bus and coach passengers group. Analysis
by TRL revealed that the car passengers group included people
travelling in cars, taxis and minibuses and hence both M1 and M2
vehicles. The bus and coach passengers group was more
straightforward and referred to people travelling in M3 vehicles. Table
25 reproduces the data from Road Casualties Great Britain 2006 (DfT,
2007) for children less than 12 years of age.
Table 25 Child passenger casualties by severity and vehicle type
during 2006 (DfT, 2007)
Severity
Killed
Seriously injured
Car passengers
including minibuses
(M1 and M2 vehicles)
26
277
Slightly injured
Bus or coach
passengers
(M3 vehicles)
0
15
6,146
534
For the purposes of this study, it was desirable to separate the car
passengers further by vehicle category. Unfortunately, the information
was not presented in this way for children in Road Casualties Great
Britain 2006 (DfT, 2007). However, it was presented in this way for all
casualties (i.e. including adults). Ratios were therefore used to estimate
the number of children killed or injured in M1 vehicles only and in M2
vehicles only. This is shown in Table 26.
Table 26 Child passenger casualties estimated by severity and
vehicle type during 2006
Severity
Killed
Seriously injured
Slightly injured
M1 vehicles
(estimated)
M2 vehicles
(estimated)
M3 vehicles
25.76
274.55
0.24
2.45
0
15
6,072.92
73.08
534
It should be noted that there is evidence that an appreciable proportion
of non-fatal injury accidents are not reported to the police and therefore
2
See Table 30a in Road Casualties Great Britain 2006 (DfT, 2007).
115
are not included in these figures (DfT, 2007). Nevertheless, the data
reveal that relatively low numbers of children are killed or seriously
injured in M2 vehicles and in M3 vehicles. Difficulties can arise when
trying to analyse accident statistics where there are only a few
occurrences of the situation being investigated. One of the most
fundamental difficulties is in establishing how well each occurrence
represents the risks for the population as a whole. These issues are
emphasised when considering injuries to children in wheelchairs. This is
highlighted in Table 27. The figures in Table 27 are based on the
assumption that children in wheelchairs represent 1 percent of the
exposure of all children.
Table 27 Estimates of number of children in wheelchairs injured by
severity and vehicle type during 2006 (based on exposure)
Severity
Killed
Seriously injured
Slightly injured
M1 vehicles
M2 vehicles
M3 vehicles
0.26
2.75
0.003
0.02
0
0.15
60.73
0.73
5.34
The research has shown that children in wheelchairs do not receive a
level of protection that is comparable to that for children in vehicle based
restraint systems. In addition, children in wheelchairs may have a lower
injury tolerance than other children. These considerations lead to the
assumption that children in wheelchairs are more likely to be injured in a
collision than other children. Estimates of the number of children in
wheelchairs that are injured based solely on exposure may not,
therefore, be adequate. TRL estimated that children in wheelchairs are
50 percent more likely to be injured in a collision than other children.
This figure was based on observations from the test programme and on
our knowledge of child biomechanics. Nevertheless, it would be useful
to revise this figure if more data becomes available in the future. Table
28 shows the estimates of the number of children in wheelchairs that are
injured when both exposure and risk are considered. The estimated
value of prevention of these casualties is shown in Table 29.
3
This figure has been rounded to two decimal places.
116
Table 28 Estimates of number of children in wheelchairs injured by
severity and vehicle type during 2006 (based on exposure and risk)
Severity
M1 vehicles
M3 vehicles
0.39
4.12
0.004
0.04
0
0.23
91.09
1.10
8.01
Killed
Seriously injured
Slightly injured
M2 vehicles
Table 29 Estimates of total value of prevention of injuries to
children in wheelchairs during 2006 (based on exposure and risk)
Severity
Killed
Seriously injured
M1
M2
M3
vehicles (£) vehicles (£) vehicles (£)
Total (£)
575,566
689,221
5,319
6,159
0
37,656
580,886
733,037
Slightly injured
1,175,110
14,141
103,329
1,292,580
Total
2,439,897
25,620
140,985
2,606,502
TRL contacted the Medicines and Healthcare products Regulatory
Agency (MHRA) to obtain additional information on child wheelchair user
casualties in order to verify the figures in Table 27. The MHRA was
unable to provide any pertinent accident records. In addition, a search
of recent internet newspaper articles was carried out. Unfortunately, this
search also found no additional accident cases in which it was stated
that a child in a wheelchair had been injured.
It is surprising that no casualty records can be found for children in
wheelchairs. As noted in Section 2.1, the number of children using
wheelchairs seems to continue to increase due to improvements in
healthcare provisions for children and vehicle accessibility. This should
lead to an increase in the number of children travelling in wheelchairs on
the roads and hence an increased exposure to the risk of injury for this
group of the population. However, the accident statistics and records do
not reflect such an increase in exposure. This leads to the hypothesis
that either accident records are not reporting the involvement of children
in wheelchairs adequately, or that the exposure to injury for children in
wheelchairs is low and in line with the data in Table 27. It is not possible
to judge accurately the extent to which these assumptions may be true.
4
This figure has been rounded to two decimal places.
117
However, it is suggested that some children in wheelchairs are involved
in UK road traffic accidents each year.
8.3
M1 vehicles (cars and taxis)
8.3.1 Vehicle design changes
Wheelchair accessible M1 vehicles are already equipped with a means
of transporting children who remain seated in their wheelchairs. Existing
technical requirements for the strength of the anchorages in these
vehicles and for the provision of space around the wheelchair are
unlikely to require significant reappraisal for the carriage of children.
The DfT may wish to relax the requirements for vehicles intended to be
used exclusively by children, but it was assumed that this would not lead
to increased engineering costs for vehicle manufacturers.
The provision of a head and back restraint is the most significant vehicle
design change that is necessary. When a wheelchair is forward facing,
a head and back restraint prevents the head and neck from extending
rearwards when the occupant has moved back into their seated position
following a collision. A head and back restraint is the only vehicle based
means of ensuring that children in wheelchairs are provided with a level
of protection from this type of loading that is comparable to that for
children in child restraints (or vehicle seats). When a wheelchair is rear
facing, a head and back restraint is the only means of reducing the risk
of serious head and neck injury in a collision.
8.3.2 Annual production estimates
Le Claire et al. (2003) estimated that there were 3,000 wheelchair
accessible vehicles, of M1 class, produced each year in which
wheelchair seated passengers travel forward facing. Additionally,
Le Claire et al. (2003) estimated that there was the same number of M1
vehicles in which wheelchair seated passengers travel rear facing.
8.3.3 Cost estimates
The estimated cost incurred to install a head and back restraint in an M1
vehicle is £ 500 per vehicle (Le Claire et al., 2003). To install these
features in 6,000 vehicles would cost £ 3,000,000.
118
8.4
M2 vehicles (minibuses)
8.4.1 Vehicle design changes
Wheelchair accessible M2 vehicles are already equipped with a means
of transporting children who remain seated in their wheelchairs. Existing
technical requirements for the strength of the anchorages in these
vehicles and for the provision of space around the wheelchair are
unlikely to require significant reappraisal for the carriage of children.
The DfT may wish to relax the requirements for vehicles intended to be
used exclusively by children, but it was assumed that this would not lead
to increased engineering costs for vehicle manufacturers.
The provision of a head and back restraint is the most significant vehicle
design change that is necessary. A head and back restraint prevents
the head and neck from extending rearwards when the occupant has
moved back into their seated position following a collision. A head and
back restraint is the only vehicle based means of ensuring that children
in wheelchairs are provided with a level of protection from this type of
loading that is comparable to that for children in child restraints (or
vehicle seats).
8.4.2 Annual production estimates
Le Claire et al. (2003) estimated that 10,000 vehicles are registered
annually, of which 2,000 were believed to be wheelchair accessible.
These figures were based on M2 vehicles with no more than 16
passenger seats.
8.4.3 Cost estimates
The estimated cost incurred to install a head and back restraint in an M2
vehicle is £ 500 per vehicle, based on the cost proposed by Le Claire et
al. (2003) for an M1 vehicle. To install these features in 2,000 vehicles
would cost £ 1,000,000.
8.5
M3 vehicles (buses and coaches)
8.5.1 Vehicle design changes
Vehicles intended to carry standing passengers (i.e. urban buses) are
not required to be fitted with seat belts and provide only limited
protection in the event of a collision. Research carried out in this project
(see Section 7) showed that the measures in place to prevent
wheelchair movement into the gangway could be improved. However, it
119
was assumed that these improvements could be achieved without
significant vehicle costs.
Wheelchair accessible M3 vehicles that do not carry standing
passengers are already equipped with a means of transporting children
who remain seated in their wheelchairs. Existing technical requirements
for the strength of the anchorages in these vehicles and for the provision
of space around the wheelchair are unlikely to require significant
reappraisal for the carriage of children.
The provision of a head and back restraint is the most significant vehicle
design change that is necessary. A head and back restraint prevents
the head and neck from extending rearwards when the occupant has
moved back into their seated position following a collision. A head and
back restraint is the only vehicle based means of ensuring that children
in wheelchairs are provided with a level of protection from this type of
loading that is comparable to that for children in child restraints (or
vehicle seats).
8.5.2 Annual production estimates
Le Claire et al. (2003) estimated that there are 100 coaches replaced
each year with new wheelchair accessible versions. Since then, the
number of buses and coaches produced each year has remained fairly
constant (SMMT, 2007). However, it is recognised that the proportion of
wheelchair accessible coaches may have increased, due to the Public
Service Vehicles Accessibility Regulations 2000 (SI 2000 No. 1970; as
amended).
8.5.3 Cost estimates
The estimated cost incurred to install a head and back restraint in an M3
vehicle is £ 500 per vehicle, based on the cost proposed by Le Claire et
al. (2003) for an M1 vehicle. To install these features in 100 vehicles
would cost £ 50,000.
8.6
Wheelchairs
8.6.1 Wheelchair design changes and indicative cost estimates
Vehicle design changes will not address all of the issues identified in the
project. Changes in wheelchair design and performance (in a collision)
are also needed to provide children in wheelchairs with a level of
protection that is comparable to that for children in child restraints or
vehicle seats. The key wheelchair design and stiffness issues could be
120
addressed by the adoption of technical requirements that are based on
the deceleration pulse in UNECE Regulation 44, a performance criterion
for abdomen loading, performance criteria for dummy loads and a rear
facing front impact test. These areas are discussed in this section.
It is TRL’s experience that the amount of research and development that
is invested differs greatly from organisation to organisation. This
experience has been gained through working with the child restraint
industry over several years. TRL expects that similar differences exist in
the wheelchair industry and it would be necessary, therefore, to conduct
an extensive and wide ranging consultation to ensure that any figures
were representative. This was beyond the scope of this cost analysis
and hence the costs presented here are estimates based on TRL’s
experience in other industries. These estimates are for indicative
purposes only.
Requirements based on UNECE Regulation 44 deceleration pulse
The test pulse used in UNECE Regulation 44 could be adopted for use
in wheelchair testing with some effort to define the test conditions. Once
some draft text explaining the test conditions had been written in
preparation for inclusion in the wheelchair testing standard, it would only
remain to have the text approved. This is likely to take some effort in
terms of preparing sufficient documents which contain justification for the
change and canvassing groups who may vote on such an amendment.
The cost of this effort may be in the region of £ 10,000.
Once the testing requirements have been changed, then the wheelchair
manufacturers will need to react to the change and develop more robust
wheelchair designs. There are about 35 manufacturers of wheelchairs
which currently sell products in the UK. Some of these products may
meet the new requirements with little or no investment, while others may
need significant redesign. Depending on the extent of the modifications
required, each manufacturer would be expected to invest around
£ 50,000 to develop more robust wheelchair designs. This investment
would need to cover engineering evaluation, perhaps physical testing
and analysis of design efficacy, through a number of potential design
iterations. Multiplication of the cost per manufacturer by the number of
manufacturers results in a value of £ 1,750,000 for research and
development undertaken by wheelchair manufacturers.
Manufacturing costs would be expected to consist of changes in tooling
and the manufacturing process as well as additional material costs.
Tooling changes would depend greatly on the extent to which existing
121
wheelchairs need to be modified, but could be in the region of £ 10,000
to £ 200,000 per manufacturer. Material costs could be in the region
between £ 5 and £ 20 per wheelchair. Therefore, the total
manufacturing costs could be between £ 850,000 and £ 5,500,000.
The total cost to society to adopt technical requirements that are based
on the deceleration pulse in UNECE Regulation 44 could range from
£ 2,610,100 to £ 7,250,000.
Performance criterion for abdomen loading
One of the most direct means of driving improvements in occupant
protection for children in wheelchairs would be to set an abdominal
loading criterion for use in the front impact dynamic test evaluations of
the wheelchairs. This is not a trivial matter, as currently the child
dummies available for use in such testing do not have robust
instrumentation with which to measure dynamic abdominal penetration
or loading. Therefore, some consideration of the potential options for
such a criterion would be necessary. It would be expected that a
targeted investigation would be needed to decide on the best option for
a criterion and to set a limit. This investigation could cost in the region of
£ 150,000. Of course, the cost associated with such an investigation
would depend on the extent to which the criterion is related to the risk of
injury to children in wheelchairs. Most simply, and with minimal cost, this
could involve some pragmatic setting of a limit for the criterion.
Once the criterion is set, effort would be required to have this approved
for use in test procedures. This could cost in the region of £ 50,000.
Wheelchair manufacturers would then need to evaluate their products
against the criterion and develop design solutions to limit abdominal
loading. The project demonstrated relatively straightforward ways in
which wheelchairs could be designed to improve the path of the seat
belt. Similar solutions could be implemented at low cost, although it is
recognised that some investment would be needed. If each
manufacturer invested £ 10,000 to improve this aspect of their range, the
total cost to the industry could be around £ 350,000.
The total cost to society to adopt a performance criterion for abdomen
loading could range from £ 400,000 to £ 550,000.
Performance criterion for dummy loads
It is expected that some benefits in the occupant restraint afforded to
children in wheelchairs could be provided with the introduction of
conventional dummy based acceleration criteria. The limits for these
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criteria should be easier to set as limits have already been proposed for
the evaluation of other child restraint systems. This assumes that the
criteria could be adopted without large revisions; an assumption which
has yet to be confirmed. However, if this was the case, the costs would
be expected to be significantly lower than those associated with the
development of an appropriate abdominal loading criterion. It should be
noted, though, that the benefits with respect to the reduction of
abdominal injuries would also be smaller as the criteria would not be
targeted at that body region.
Some work would be required to have the dummy based performance
limits approved for use in test procedures. This could cost in the region
of £ 50,000. Wheelchair manufacturers would then need to evaluate
their products against the criteria and perhaps improve their designs.
Some of these products may meet the new requirements with little or no
investment, while others may need significant redesign. Depending on
the extent of the modifications required, each manufacturer would be
expected to invest around £ 50,000 to meet the new dummy
performance limits. This investment would need to cover engineering
evaluation, perhaps physical testing and analysis of design efficacy,
through a number of potential design iterations. Multiplication of the cost
per manufacturer by the number of manufacturers results in a value of
£ 1,750,000 for research and development undertaken by wheelchair
manufacturers.
Additional manufacturing costs could comprise changes in tooling and
the manufacturing process as well as additional material costs. Tooling
changes would depend greatly on the extent to which existing
wheelchairs need to be modified, but could be in the region of £ 10,000
to £ 100,000 per manufacturer. Material costs could be in the region of
£ 5 to £ 20 per wheelchair. Therefore, the total manufacturing costs
could be between £ 850,000 and £ 5,500,000.
The total cost to society to adopt performance criteria for dummy loads
could range from £ 2,650,000 to £ 7,300,000.
Rear facing front impact test
There are several components that will contribute to the societal costs
associated with the introduction of a rear facing frontal impact test for
wheelchairs. Firstly, the test procedure would need to be developed,
which would require a targeted investigation to derive, evaluate and
validate appropriate test conditions. For the second stage, it would be
necessary to obtain approval for this new test requirement to be
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adopted. Some testing of wheelchair products against the new
requirements would be necessary along with enforcement of compliance
with the requirement if it is mandated in some way. Finally, the reaction
of the wheelchair manufacturers to the new requirement would be
important, along with their provision of new designs which comply with it.
The investigation to develop the new test procedure may cost society up
to £ 150,000. A further £ 50,000 could be necessary to provide sufficient
justification and political pressure to have the procedure approved. For
new wheelchair products to be tested according to the procedure,
perhaps £ 50,000 could be needed to cover the costs of the testing and
compliance by each wheelchair manufacturer.
Each wheelchair manufacturer may then incur costs of £ 100,000 to
ensure that new designs of wheelchair meet the requirement. This
would need to cover engineering evaluation, physical testing and
analysis of design efficacy. Multiplication of the cost per manufacturer
by the number of manufacturers results in a value of £ 3,500,000.
Manufacturing costs would be expected to consist of changes in tooling
and the manufacturing process as well as additional material costs.
Tooling changes would depend greatly on the extent to which existing
wheelchairs need to be modified, but could be in the region of £ 10,000
to £ 100,000 per manufacturer. Material costs could be in the region of
£ 5 to £ 20 per wheelchair. Therefore, the total manufacturing costs
could be between £ 850,000 and £ 5,500,000.
The total cost to society to adopt a rear facing front impact test could
range from £ 6,300,000 to £ 10,950,000.
8.7
Comparison of benefits and costs
Five key changes or measures to improve the level of protection
afforded to children in wheelchairs have been discussed in this section.
These comprise one vehicle measure (a head and back restraint) and
four wheelchair measures (technical requirements based on the
deceleration pulse in UNECE Regulation 44, a performance criterion for
abdomen loading, performance criteria for dummy loads and a rear
facing front impact test). The benefit of each measure in terms of the
casualty cost saving was estimated by multiplying the child in wheelchair
casualties in Table 27 by an effectiveness value for each measure. The
effectiveness values are shown in Table 30. An effectiveness value of
0.2 means that the measure is estimated to be effective for 20 percent of
all casualties.
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Table 30 Effectiveness values used in the analysis of benefits
Proposed measure
Effectiveness
Head and back restraint
ECE Regulation 44 deceleration pulse
Performance criterion for abdomen loading
Performance criteria for dummy loads
Rear facing front impact test
0.2
0.2
0.2
0.1
0.05
The value of prevention was recalculated using the number of casualties
that would be expected if each measure was implemented. It was
assumed, for the purpose of this analysis, that the measures are
complementary, although it is recognised that some casualties would be
mitigated by more than one of the measures. In addition, it was
assumed that the measures taken would reduce fatal injuries to serious
and serious injuries to slight.
For simplicity, the total value of prevention for each measure was
determined across all vehicle categories and injury severities. These
figures were compared with the costs associated with the
implementation of each measure set out in Sections 8.3 to 8.6. This is
shown in Table 31. Further analysis of the benefits and costs is shown
in Table 32.
Table 31 Comparison of benefits and costs
Proposed measure
Head and back restraint
UNECE Regulation 44
deceleration pulse
Performance criterion for
abdomen loading
Performance criteria for
dummy loads
Rear facing front impact
test
Benefit (£)
Cost (£)
From
To
496,946
4,050,000
4,050,000
496,946
2,610,000
7,250,000
496,946
400,000
550,000
248,473
2,650,000
7,300,000
124,236
6,300,000
10,950,000
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Table 32 Analysis of benefits and costs
Benefit – cost (£)
Benefit/cost (£)
Proposed measure
Best case Worst case
Head and back
restraint
UNECE Regulation
44 deceleration pulse
Performance criterion
for abdomen loading
Performance criteria
for dummy loads
Rear facing front
impact test
8.8
Best case
Worst
case
-3,553,054
-3,553,054
0.123
0.123
-2,113,054
-6,753,054
0.190
0.069
96,946
53,054
1.242
0.904
-2,401,527
-7,051,527
0.094
0.034
-6,175,764 -10,825,764
0.020
0.011
Summary
Very limited information was available from which to gather accurate
data for the number of journeys made by children in wheelchairs and for
their involvement in vehicle collisions. However, it is likely that a
relatively large number of journeys are made without significant incident.
In these circumstances, it might appear that there are limited benefits to
society from new safety measures. This is because such analyses are
based on estimates of the reduction in injuries in terms of their economic
cost. In fact, there are other benefits of new safety measures, when
considering the protection of children in wheelchairs. For example,
providing children in wheelchairs with a level of protection that is
comparable to that for children travelling in a vehicle based restraint
system would help to meet an important responsibility of society to these
children.
The project highlighted that vehicle design changes alone will not
address all of the issues identified for children in wheelchairs.
Wheelchair design changes, encouraged by changes in the relevant
performance requirements, are also necessary. A proportion of these
costs would be incurred by the wheelchair manufacturing industry. It is
TRL’s experience that these costs can vary greatly from organisation to
organisation. It would be necessary, therefore, to consult a very wide
range of organisations to obtain representative estimates of the costs of
new requirements. As such, a wide ranging consultation was beyond
the scope of this project. TRL provided indicative costs based on our
experience of other industry sectors.
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9 Discussion
The results for each vehicle category and wheelchair direction were
discussed in detail within Sections 3 to 7. This section provides an
overview of the findings of the whole study and discusses some
limitations of the research.
9.1
General observations
The main aim of the project was to examine the safety of children in
wheelchairs in M category vehicles. The key question was whether
children who remain seated in their wheelchair are afforded a level of
protection in a front impact that is comparable to that for children
travelling in a vehicle based restraint system. Some 32 sled tests were
carried out with various wheelchairs and child dummies. In addition,
eight sled tests were carried out with the corresponding dummies seated
in child restraints or vehicle seats.
The purpose of a restraint system is threefold. Firstly, it must minimise
the risk of ejection from the vehicle. Secondly, it must minimise the risk
of body contact with the interior of the vehicle. Thirdly, it must absorb
and distribute the impact forces over the strongest parts of the body.
The three point seat belt is the main type of restraint system for adults in
road vehicles, but the vehicle seat also has an important role.
The vehicle seat provides a stable base of support for the occupant
during normal driving and in the event of a collision. It is designed (and
tested) to work with the restraint system and can improve the interaction
between the occupant and the restraint through anti-submarining
features. The vehicle seat also contributes to the management of the
occupant’s loads during a crash and supports the head and neck during
the rebound phase of a front impact (i.e. when the occupant moves back
into their seat and their head extends rearwards) or during a rear impact.
Children require special attention because their tissues have different
biomechanical properties compared with adults. Their needs must be
met with an additional child restraint system, although they are permitted
to use the vehicle seat and adult seat belt in certain circumstances in
some vehicles.
The main purpose of a wheelchair is to aid the mobility of the user.
However, wheelchairs are being used increasingly in vehicles because it
is inconvenient or sometimes impossible to transfer easily to a vehicle
seat. In these circumstances, a wheelchair takes the place of a vehicle
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seat, although this function may not have been in mind when the
wheelchair was designed.
A wheelchair tie-down and occupant restraint system is used to hold the
wheelchair and occupant in place during normal driving and in the event
of a collision. A wheelchair user has the right to expect a comparable
level of protection from their wheelchair and restraint system as any
other passenger seated in the vehicle. This was explored in the project.
9.2
Wheelchair restraint system
9.2.1 Forward facing wheelchairs
A production model four point wheelchair tie-down system was used for
forward facing wheelchairs in the test programme. The webbing straps
were secured to the floor of the impact sled in the same manner as they
would be in a typical vehicle. The wheelchair tie-down system kept the
wheelchairs in place during the test programme with little or moderate
displacement. This was expected since this aspect of the performance
of the wheelchair tie-down system is addressed in ISO 10542-1:2001
and ISO 10542-2:2001. The distance between the tracking was
330 mm; the tie-down manufacturer’s tested dimension and the distance
used by TRL for routine wheelchair testing according to ISO
7176-19:2001. The effect of different tracking widths was not examined,
but it would appear that 330 mm was appropriate to maintain the stability
of children’s wheelchairs during normal driving or a collision.
9.2.2 Rear facing wheelchairs
A two point wheelchair tie-down system was used for the rearward
facing wheelchairs in the test programme. The webbing straps were
secured to the floor of the impact sled after passing them through a slot
in the surrogate bulkhead in a similar manner as they would in a typical
vehicle. The bulkhead that separates the driver and passenger
compartments is the main restraint for the wheelchair, but wheelchair tiedowns are also necessary to prevent the wheelchair from moving around
the passenger compartment in normal driving and during the rebound
phase of a collision. When a wheelchair is rear facing, rebound refers to
the period where the occupant and their wheelchair move away from the
bulkhead. The tie-down system was effective in this respect, but several
of the wheelchairs rotated about the axis of the rear wheels because the
front wheels were unrestrained and because the back of the wheelchair
was not well supported. When this occurred, it usually resulted in a
secondary impact between the dummy (through the wheelchair
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backrest) and the bulkhead surface. In contrast, the dummy ‘rode down’
the impact against the bulkhead when it was seated on the rear facing
tip-up seat. Restraining the front wheels would increase the loads on
the wheelchair backrest and increase the time taken to restrain the
wheelchair. A head and back restraint that supports the wheelchair and
the occupant would be the best solution.
9.3
Occupant restraint system
9.3.1 Forward facing wheelchairs
A surrogate three point seat belt was used when the wheelchairs were
forward facing in the test programme. This included an inertia reel and
an upper anchorage point for the diagonal part of the belt. The relative
performance of an upper anchorage point for the diagonal belt compared
with a floor mounted anchorage was not examined. In previous
research for the DfT, Le Claire et al. (2003) found that a floor mounted
anchorage resulted in greater head excursion and greater lumbar spine
loads in an adult dummy compared with an upper anchorage. It seemed
likely that similar findings would be made with child dummies so it was
agreed with the DfT to use an upper anchorage point in all tests in this
project. This represents the best practice for the restraint of all
wheelchair users including children.
The surrogate seat belt kept the dummy within each wheelchair during
the test programme and prevented excessive head and body excursion
if the wheelchair was robust. This was expected since this aspect of the
seat belt’s performance was examined before the test programme with a
dynamic test according to ISO 10542-1:2001. This demonstrated that
the surrogate occupant restraint was similar in this respect to other
products on the market that also meet the requirements of the Standard.
In addition to preventing ejection and limiting excursion, the surrogate
seat belt ensured a reasonable ride-down of the sled deceleration for the
dummy. However, it was also the case that the dummy accelerations
and forces varied quite markedly across the different wheelchair types.
This highlighted the potential influence of the wheelchair as a vehicle
seat on the protection that a child would receive in a crash. The
management of the occupant’s loads is not currently addressed in ISO
7176-19:2001; hence it was unsurprising that the dummy loads varied in
this way.
A seat belt must also distribute the restraint forces over the strongest
parts of the body. In view of this, the surrogate seat belt was designed
129
to achieve a good fit for the child dummy irrespective of the type and
model of the wheelchair. Nevertheless, in some cases the side of the
wheelchair obstructed the ideal path of the lap part of the belt, resulting
in greater abdomen loading. Furthermore, the seat belt was likely to
load the abdomen when the wheelchair compressed or deformed during
the impact. Although the path of the seat belt needed to be improved
when the dummy was seated on the vehicle seat, it would seem that a
child in a wheelchair would be exposed to a greater risk of abdomen
injury than a child in a vehicle seat. A child in a child restraint system
receives the best protection because, in the case of harness systems,
there is a fifth point or crotch strap to keep the lap straps on the pelvis,
or in the case of booster systems, there are guides to ensure the lap belt
passes over the top of the thighs.
The side view angle of the lap part of the seat belt fell within the range
specified in ISO 10542-1:2001 in every test. The belt angle and location
of the anchorages was influenced by the use of tracking behind the
wheelchair and by the wheels or tipping levers of the wheelchair. The
location of the lap belt anchorages in the vehicle was important, but it
was also important for the wheelchair to allow the seat belt to be fitted
easily over the top of the occupant’s thighs. The wheelchair must also
maintain a stable seating position for the occupant throughout a collision
to reduce the risk of the pelvis passing under the lap part of the belt.
The ideal solution would be for the wheelchair to guide the seat belt and
hold it in place during the impact in the same way as a booster seat. A
wheelchair integrated restraint harness is another solution, although this
would increase the loads on the wheelchair.
9.3.2 Rear facing wheelchairs
The surrogate seat belt was also used when the wheelchairs were
rearward facing in the test programme. The anchorage positions on the
surrogate bulkhead were similar to those observed in real vehicles.
Although some of the issues related to the fit of the seat belt were also
relevant to the rear facing situation, the main purpose of the seat belt
was to restrain the dummy in rebound when the belt loads were much
lower.
9.4
Head and back restraint
9.4.1 Forward facing wheelchairs
Vehicle seats are designed to support the head and neck of the
occupant. However, very few M1 or M2 vehicles provide a head and
130
back restraint when they transport forward facing wheelchair users. A
head and back restraint was not used, therefore, in the test programme.
As a result, the head of the dummy was unsupported and extended
rearwards during the rebound phase of each impact test. Some
wheelchairs included a headrest, but the dummy either rode up over the
headrest or pushed it away. A child travelling in this way would be at
risk of head contact with the vehicle if there was insufficient space
behind the wheelchair. They would also be at risk of neck injury. The
neck measurements were generally quite low during rebound; however,
the neck was bending below the level of the instrumentation. It was
possible, therefore, that the dummy was not well suited to neck injury
prediction during extension. Nevertheless, the head and neck
kinematics did suggest that a child would be at risk of soft tissue neck
injury. A child travelling in a child restraint or a vehicle seat would not be
exposed to this risk because their head would be supported during
rebound. A head and back restraint would provide a child in a
wheelchair with a comparable level of protection during rebound as a
child in a child restraint or a vehicle seat. However, a wheelchair
integrated solution might be necessary for a child in a wheelchair with
supportive seating.
9.4.2 Rear facing wheelchairs
Rearward facing wheelchairs were positioned against a generic vehicle
bulkhead during the test programme. The head of the dummy was not
supported by the bulkhead and extended rearwards during each test.
This usually resulted in significant bending of the neck and sometimes
head and other body contact with rigid parts of the bulkhead. The
dummy measurements were generally high when either of these events
occurred. There was a similar outcome when the dummy was seated on
the rear facing vehicle (tip-up) seat. However, the loads were
sometimes lower because the dummy ‘rode down’ the impact against
the bulkhead surface. A head and back restraint would increase the
level of protection afforded to children in wheelchairs and to children in
rear facing tip-up seats. The head and back restraint in the vehicle
would need to be compatible with children’s wheelchairs to be effective.
This would be relatively straightforward for manual and electric
wheelchairs; however, buggies and wheelchairs with supportive seating
would be difficult to accommodate.
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9.5
Wheelchair design and stiffness
9.5.1 Forward facing wheelchairs
The wheelchairs used in the test programme deformed to a greater
extent than desirable for a vehicle seat during a collision. When the
wheelchairs were forward facing, the deformation usually led to greater
dummy accelerations and forces or greater loading to vulnerable body
regions such as the abdomen. The UNECE Regulation 44 test
conditions used in the study were slightly more stringent than the ISO
Standards. Furthermore, the ISO Standards do not address occupant
loading. A particular issue was found with the performance of a tested
base with a tested seating system from different manufacturers.
Although the mass of the seating system and dummy were within the
mass limit for the base when used with its own seat, the device failed
during the test.
9.5.2 Rear facing wheelchairs
Most wheelchairs were unable to withstand the forces of the impact
when they were used rear facing. ISO 7176-19:2001 does not include a
rear facing front impact test and most manufacturers state that the
wheelchair should be used forward facing in a vehicle. A head and back
restraint may improve the structural performance of rear facing
wheelchairs, but it may also be necessary to carry out rear facing sled
tests. This would ensure that wheelchairs are tested to reflect the way
they will be used in certain vehicles.
9.6
Limitations of the project
As a starting point, this project addressed the front impact of vehicles
only. It may be desirable, in the future, to examine the safety of children
in wheelchairs in vehicles involved in side or rear impacts. Similarly, the
project addressed the safety of children in wheelchairs when best
practice was followed and when the equipment was used correctly.
Misuse was not included, but could be addressed by improving the
information provided to parents and transport operators. Children in
wheelchairs are sometimes provided with a range of equipment and
accessories that are attached to their wheelchairs to aid their
independence. It might be impossible to remove the equipment for
transport if, for instance, it is used for breathing assistance or for
communication. The use of such equipment was outside the scope of
the project, but it may be worthwhile to consider its effects in the future.
132
Finally, it should be noted that child dummies approximate the weight
and size of an average child at the age they are intended to represent.
Disabled children are not likely to be included in studies of child
anthropometry and they could have different biomechanical properties.
Child dummies may not, therefore, be representative of the general
population of children who use wheelchairs. Nevertheless, child
dummies are the best available means of investigating the safety of
children in wheelchairs in vehicles. In fact, dummies represent a very
small group of children. However, they have contributed to significant
improvements in the design and performance of child restraint systems
for all children. It follows that while the dummies may not represent all
child wheelchair users, their use in dynamic tests could achieve similar
improvements in wheelchair safety for all children.
Dummies are designed to respond to load in the same way as a living
human under the same conditions. There is very little biomechanical
data for children on which to base the requirements for child dummies.
Biomechanical response requirements for adult dummies are therefore
scaled to give corresponding requirements for children. The techniques
used and the assumptions made can influence the dummy
requirements. The Hybrid III Series of child dummies was used in the
project because it represented the best option in terms of measurement
capacity and published injury criteria. The injury criteria were developed
for non-disabled children. It is possible that children in wheelchairs may
have a lower threshold for injury than other children, although no
literature was available about this at the time of writing. If this is the
case, measures to reduce the loads experienced by disabled children in
a collision could be very important. The Hybrid III dummies were not
designed to be used rear facing so caution was used when interpreting
the test results. Some injury criteria intended for forward facing
dummies were invalid when the dummies were rear facing. However, for
the purposes of comparative testing it was possible to deduce that a
dummy measurement of reduced amplitude indicated a reduced risk of
injury, provided that the measurement corresponded with the type of
loading expected in children.
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10 Conclusions
•
There is no specific legislation in place to address the protection of
children in wheelchairs in the event of a collision.
•
Based on the findings of this research, children in wheelchairs do
not receive a level of protection comparable to that for children in
child restraints or vehicle seats.
•
Changes in legislation are required to address and hence improve
the protection afforded to children in wheelchairs.
•
The protection of children in wheelchairs is influenced by the
vehicle, the restraint system and the wheelchair. All three areas
must be addressed for improvements in protection to be made.
•
The greatest improvements would be realised if vehicle, restraint
system and wheelchair manufacturers worked together.
•
There must be sufficient space in the vehicle to reduce the risk of
child head contact with the interior.
•
A head and back restraint needs to be provided for children,
irrespective of the direction they face in the particular vehicle.
•
A three point seat belt is essential to restrain children in
wheelchairs. The best practice is to anchor the diagonal part of the
belt to the vehicle above the shoulder level.
•
The seat belt should distribute the restraint forces over the strongest
parts of a child’s anatomy. Wheelchairs must not interfere with or
obstruct the belt.
•
A wheelchair needs to be capable of withstanding the forces in a
collision of appropriate severity if it is intended for use in a vehicle.
•
The dynamic test conditions in UNECE Regulation 44 are
appropriate to examine the performance of safety equipment in M1
and M2 vehicles.
•
The dynamic test conditions in the ISO Standards for wheelchair
transportation are less stringent than the test conditions in UNECE
Regulation 44.
134
•
Wheelchairs must be designed, in combination with occupant
restraints, to manage the child’s loads during a collision.
135
11 Recommendations
11.1 M1 and M2 forward facing
11.1.1
Vehicle anchorages
There are a number of different vehicle anchorage systems in use with
wheelchair tie-down and occupant restraints. Rail tracking systems are
the most common, but individual anchor points are used in some
vehicles. Docking systems are also available, although at the present
time these are more likely to be found in private vehicles. Differences
between these systems are unlikely to affect the loading to a child in a
collision, providing that it is part of a complete system that meets the
requirements of ISO 10542-1:2001. Hence rail tracking, individual
anchors and docking systems can all be recommended for vehicles that
may be used to transport children in wheelchairs.
The location of the anchorages in the vehicle needs careful
consideration. The tested lateral dimension between the anchorages is
330 mm for most wheelchair tie-down systems. This distance is
recommended for children’s wheelchairs, unless the manufacturer states
otherwise. The wheelchair should be attached so that the tie-downs
achieve an angle of 45˚. The occupant restraint anchorages should be
positioned to ensure that the lap part of the seat belt rests across the top
of the thighs or very low over the front of the pelvis. The preferred zone
of 30˚ to 75˚ to the horizontal is described in the ISO Standards, but TRL
recommends that lap belt angles below 45˚ are avoided, where possible.
This is important for keeping the belt on the pelvis during a collision.
Le Claire et al. (2003) recommended that the strength of vehicle
anchorages be assessed in a static strength test and proposed
requirements for the test. Work is currently ongoing to finalise these
requirements. Children and their wheelchairs generate lower forces at
the vehicle anchorages than adults and their wheelchairs. It would,
therefore, be possible to develop separate requirements for vehicles that
are intended to carry children only. Clearly, there would be a number of
issues to consider if separate requirements were developed that were
dependent on the weight of the occupant or of their wheelchair.
Nevertheless, it might be inappropriate to oblige someone to purchase a
vehicle that is stronger and hence more expensive than they require. If
the DfT wishes to make such requirements for the transport of children,
136
TRL recommends the following performance limits for the static strength
test:
•
When the anchorage of a rear wheelchair tie-down is combined with
the lower anchorage of an occupant restraint system, the combined
anchorage point should be able to sustain a force of 28.50 kN when
applied along the longitudinal axis of the vehicle and at an angle of
45˚ to the floor.
•
Each of the front wheelchair tie-down anchorages should be able to
sustain a force of 2.65 kN when applied along the longitudinal axis
of the vehicle and at an angle of 45˚ to the floor.
•
The upper anchorage should be able to sustain a force of 7.30 kN
applied at an angle of 45˚ along the longitudinal axis of the vehicle
and at an angle of 45˚ to the side wall.
•
It is suggested that these forces should be sustained without failure
for a minimum time period. A minimum period of 0.2 seconds would
seem to be appropriate, based on the duration of typical impact
pulses.
11.1.2
Occupant restraint
It is essential that children in wheelchairs are restrained with a three
point seat belt. TRL recommends that the diagonal part of the seat belt
is anchored to the vehicle above the shoulder level. The lap part of the
seat belt may be attached to the vehicle floor or to the rear wheelchair
tie-downs. Systems that attach to the rear wheelchair tie-downs appear
to provide the best fit, although it was not part of this research to
evaluate specific systems. Any occupant restraint should be installed to
achieve the best possible belt path for the wheelchair user.
Wheelchair integrated seat belts or harnesses represent the best
solution for children, but increase the loads on the wheelchair.
Integrated restraints are recommended when the wheelchair has been
designed to accommodate an integrated restraint system.
Finally, it is recommended that the occupant restraint incorporates an
inertia reel to manage the belt loads applied to the child. Although seat
belts are designed to apply the forces to the strongest parts of the
anatomy, the skeletal structures of children remain under development
throughout childhood. A static three point seat belt should be avoided
because it would apply higher loads to these structures.
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11.1.3
Head and back restraint
TRL recommends that a head and back restraint is provided for children
in wheelchairs. This is necessary to prevent the head and neck from
extending rearwards when a child moves back into their seated position
following a collision. It is very important to prevent this motion; firstly, to
reduce the risk of head and neck injury due to head contact with the
vehicle interior behind the wheelchair, and secondly, to reduce the risk
of soft tissue neck injury due to overextension of the head and neck. A
child’s skull is less stiff than an adult’s and must be protected from
impact with the vehicle interior. In addition, the muscles and ligaments of
the neck are not fully developed; hence children are particularly
vulnerable to overextension of the head and neck.
A vehicle seat or a child restraint system supports the head and neck of
a child, thereby reducing the likelihood of injury. A head and back
restraint is therefore the only means of ensuring that children in
wheelchairs are provided with a level of protection that is comparable to
that for children in child restraints (or vehicle seats) when they move
back into their seated position following a collision. A vehicle based
head and back restraint may be incompatible with some wheelchair
types. In this case, a wheelchair integrated solution is recommended.
A vehicle based head and back restraint would need to meet a series of
requirements to cover its dimensions, energy absorption and strength.
Le Claire et al. (2003) proposed a series of requirements, which seem to
be appropriate for both adult and child passengers, although it was not
part of this research to evaluate these requirements. A wheelchair
integrated head and back restraint should be assessed during the
dynamic test of the wheelchair for which it is intended to be used. This
is because testing with surrogate devices can lead to unexpected results
when products are used together.
11.1.4
Occupant space
Children in wheelchairs must be provided with sufficient space to reduce
the risk of head contact with the interior. Although energy absorbing
materials can be added to the interior of a vehicle, glancing head contact
on relatively soft materials can result in brain injury through rotation
mechanisms and neck injury through shear forces at the junction of the
head and neck.
Le Claire et al. (2003) recommended a space for a wheelchair and
occupant in an M1 or an M2 vehicle. The requirements should not be
138
relaxed for transporting children because the displacement of a child in a
collision could be similar to that of an adult.
11.1.5
Wheelchair design and stiffness
When a child is travelling in a vehicle, they have a number of key needs
that must be met by their seat. Firstly, the seat must provide a stable
base of support in normal driving and in the event of a collision. The
structural characteristics of the seat are therefore very important.
Secondly, the seat must allow the seat belt to follow the correct path
around the strongest parts of the child’s anatomy, while avoiding the
weaker areas. Furthermore, the seat must help to maintain the correct
belt geometry throughout a collision by preventing the pelvis from
moving downwards and hence under the lap part of the seat belt.
Finally, the seat must work with the restraint system to manage the
child’s deceleration. Wheelchairs do not perform these functions
adequately for children, when compared with child restraint systems or
even vehicle seats. Wheelchairs must be included, therefore, in any
effort to improve the level of protection afforded to children in a collision.
The structural characteristics of children’s wheelchairs need to improve
to provide a level of protection that is comparable to that for child
restraint systems. Manufacturers that design wheelchairs for use in a
vehicle must develop products with the necessary performance
characteristics. TRL recommends that wheelchairs are assessed to the
same level of impact severity as that described in UNECE Regulation 44
for the approval of child restraint systems.
There are several ways that children’s wheelchairs could be designed to
improve the path of the seat belt and maintain the child’s position in a
crash. These solutions would be encouraged if there was a
performance criterion for abdomen penetration included in the dynamic
test for wheelchairs. TRL recommends that a performance criterion for
belt penetration of the abdomen be developed for children’s wheelchairs
and applied with an appropriate limit during a dynamic test.
A child’s deceleration is managed by coupling them tightly to the vehicle
early in the impact and then controlling their subsequent excursion.
There are a number of solutions that could be applied in both the
wheelchair and the restraint system to optimise their performance in this
respect. Manufacturers that design wheelchairs for use in a vehicle
should develop solutions, in collaboration with restraint system
manufacturers. Performance limits are applied during the dynamic test
for child restraint systems in UNECE Regulation 44. If the DfT wishes to
139
provide comparable provision for children in wheelchairs, TRL
recommends that dummy loads are measured during dynamic tests of
children’s wheelchairs with performance limits applied that are in line
with the Regulation for child restraints.
11.2 M1 and M2 rear facing
11.2.1
Vehicle anchorages
The present system in most vehicles, whereby the wheelchair is
restrained against a bulkhead by means of a two point wheelchair tiedown system, is adequate to restrain children’s wheelchairs during the
rebound phase of a collision when the wheelchair moves away from the
bulkhead. TRL recommends that the anchorages of the two point
system are located within the bulkhead to ensure that the wheelchair is
positioned as close as possible to the bulkhead surface.
A four point wheelchair tie-down system would offer the added benefit of
preventing wheelchair rotation during an impact; however, this could
also be achieved (with additional benefits) by a head and back restraint.
This will be discussed in Section 11.2.3.
Le Claire et al. (2003) recommended that the strength of vehicle
anchorages be assessed in a static strength test and proposed
requirements for the test. Work is currently ongoing to finalise these
requirements. It was not within the scope of this study to examine
whether the requirements could be relaxed for vehicles intended to carry
only children rear facing.
11.2.2
Occupant restraint
The three point seat belt provided for wheelchair users in current
vehicles is adequate to restrain children in wheelchairs, during the later
phase of a front impact, when they move away from the bulkhead and
their wheelchair seat. It is recommended that the upper anchorage of
the diagonal part of the seat belt is adjustable to accommodate the lower
shoulder heights of children.
11.2.3
Head and back restraint
TRL recommends that a head and back restraint is provided for rear
facing children in wheelchairs. This is the only means of reducing the
risk of serious head and neck injury in a front impact. Where a vehicle
based head and back restraint is incompatible with the wheelchair, a
wheelchair integrated solution should be provided.
140
A vehicle based head and back restraint must meet a series of
requirements to cover its dimensions, energy absorption and strength.
Le Claire et al. (2003) proposed a series of requirements, which seem to
be appropriate for both adult and child passengers, although it was not
part of this research to evaluate these requirements. A wheelchair
integrated head and back restraint should be assessed during the
dynamic test of the wheelchair for which it is intended to be used, to
avoid unexpected results when the products are used together.
11.2.4
Occupant space
Le Claire et al. (2003) recommended that the space provided for a
wheelchair and occupant is at least 1,300 mm measured in the
longitudinal plane of the vehicle and 750 mm in the transverse plane of
the vehicle, up to a height of 1,500 mm measured vertically from any
part of the floor of the wheelchair space. It was not within the scope of
this research to suggest modified requirements for vehicles intended
specifically to carry children rear facing.
11.2.5
Wheelchair design and stiffness
Manufacturers of wheelchairs intended for use in a vehicle usually state
in their product literature that the wheelchair should only be used
forward facing. Nevertheless, there are vehicles in use that transport
wheelchair users facing the rear. There are well known advantages to
travelling rear facing; however, there is also a risk that a wheelchair
would be unable to withstand the forces in a collision because it had not
been designed or tested to be used in that way. Children would be
particularly at risk due to their anatomy and level of development.
A head and back restraint within the vehicle may support some
wheelchairs and improve their capacity to withstand the collision, but this
would need to be established. TRL recommends, therefore, that the
performance tests for children’s wheelchairs include a rear facing front
impact. This would reflect the way that wheelchair users travel in a
significant number of vehicles.
11.3 M3 forward facing
11.3.1
Vehicle anchorages
There are a number of different vehicle anchorage systems in use with
wheelchair tie-down and occupant restraints. Rail tracking systems are
the most common for webbing based tie-down systems, but individual
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anchor points are used in some vehicles. Docking systems are also
available, although at the present time these are more likely to be found
in private vehicles. Differences between these systems are unlikely to
affect the loading to a child in a collision, providing that it is part of a
complete system that meets the requirements of ISO 10542-1:2001.
Hence rail tracking, individual anchors and docking systems can all be
recommended for vehicles that may be used to transport children in
wheelchairs.
The location of the anchorages in the vehicle needs careful
consideration. The tested lateral dimension between the anchorages is
330 mm for most wheelchair tie-down systems. This distance is
recommended for children’s wheelchairs, unless the manufacturer states
otherwise. The wheelchair should be attached so that the tie-downs
achieve an angle of 45˚. The occupant restraint anchorages should be
positioned to ensure that the lap part of the seat belt rests across the top
of the thighs or very low over the front of the pelvis. The preferred zone
of 30˚ to 75˚ to the horizontal is described in the ISO Standards, but TRL
recommends that the further work is done to specify an appropriate zone
for children.
Le Claire et al. (2003) recommended that the strength of vehicle
anchorages be assessed in a static strength test and proposed
requirements for the test. Children and their wheelchairs generate lower
forces at the vehicle anchorages than adults and their wheelchairs.
Nevertheless, it was not within the scope of this project to investigate
whether separate requirements could be developed for M3 vehicles that
are intended specifically to carry children.
11.3.2
Occupant restraint
It is essential that children in wheelchairs are restrained with at least a
three point seat belt. TRL recommends that the diagonal part of the seat
belt is anchored to the vehicle above the shoulder level. The lap part of
the seat belt may be attached to the vehicle floor or to the rear
wheelchair tie-downs. However, TRL recommends that, where possible,
the belt is attached to the rear wheelchair tie-downs. This is likely to
provide a better path and angle of the lap belt.
Wheelchair integrated seat belts or harnesses represent the best
solution for children, but increase the loads on the wheelchair.
Integrated restraints are recommended when the wheelchair has been
designed to accommodate an integrated restraint system.
142
Finally, it is recommended that the occupant restraint incorporates an
inertia reel to manage the belt loads applied to the child. Although seat
belts are designed to apply the forces to the strongest parts of the
anatomy, the skeletal structures of children remain under development
throughout childhood. A static three point seat belt should be avoided
because it would apply higher loads to these structures.
11.3.3
Head and back restraint
TRL recommends that a head and back restraint is provided for children
in wheelchairs. This is the only means of ensuring that children in
wheelchairs are provided with a level of protection that is comparable to
that for children in child restraints (or vehicle seats) when they move
back into their seated position following a collision. A vehicle based
head and back restraint may be incompatible with some wheelchair
types. In this case, a wheelchair integrated solution is recommended.
A vehicle based head and back restraint would need to meet a series of
requirements to cover its dimensions, energy absorption and strength.
Le Claire et al. (2003) proposed a series of requirements, which seem to
be appropriate for both adult and child passengers, although it was not
part of this research to evaluate these requirements. A wheelchair
integrated head and back restraint should be assessed during a dynamic
test with the wheelchair for which it is intended to be used. This is
because testing with surrogate devices can lead to unexpected results
when products are used together.
11.3.4
Occupant space
Le Claire et al. (2003) recommended that the space provided for a
wheelchair and occupant is at least 1,300 mm measured in the
longitudinal plane of the vehicle and 750 mm in the transverse plane of
the vehicle, up to a height of 1,500 mm measured vertically from any
part of the floor of the wheelchair space. It was not within the scope of
this research to suggest modified requirements for M3 vehicles intended
to carry only children forward facing.
11.4 M3 rear facing
The following recommendations are made with regard to the non-impact
protection of children in wheelchairs in low floor buses:
11.4.1
Head- and backrest
It must be possible to position a child’s wheelchair against the backrest.
However, the gap between the handles of wheelchairs for younger
143
children is likely to be too small for the handles to pass either side of the
backrest and the base of some electric wheelchairs might extend further
rearwards than the space below the backrest.
The DfT may wish to consider modifying the dimensions and/or location
of the backrest in line with the children's wheelchair dimensions provided
by Hitchcock (2008) and reported in Section 6.1. This should be
considered alongside similar dimensions for adults’ wheelchairs to
ensure there are no conflicts between children's needs and adults’
needs for support.
11.4.2
Restricting wheelchair movement into the gangway
Regulations permit either a vertical stanchion or a horizontal rail to
restrict wheelchair movement into the gangway during normal driving
manoeuvres; however, TRL recommends that, where possible, a vertical
stanchion is used for children in wheelchairs.
The position of the stanchion is very important. The project examined
the effectiveness of the stanchion at three positions: 400 mm, 480 mm
and 560 mm rearwards of the front of the wheelchair space. The
stanchion was effective only when it was positioned 560 mm from the
front of the wheelchair space. However, the wheelchairs were not
positioned directly against the backrest due to their handles or due to
their batteries.
The DfT may wish to consider modifying the range permitted for the
position of the stanchion such that the minimum distance rearwards from
the front of the space is increased. However, this could affect access to
the wheelchair space for some larger wheelchairs. Hence TRL
recommends that further research is carried out to investigate these
issues.
The stability of an unrestrained wheelchair supported by a backrest is
influenced by the front wheels. The wheelchair is more likely to move
into the gangway when the front wheels are able to rotate on their
castors. TRL recommends that further work is carried out to establish
the feasibility of locking the front wheels of children’s wheelchairs.
144
Acknowledgements
The work described in this report was carried out in the Vehicle
Engineering Division of TRL. The authors are grateful to Marianne Le
Claire for carrying out the quality review and auditing of this report.
TRL appreciates the support of the DfT in carrying out this research. The
research was possible due to the DfT’s commitment to an accessible
transport system with consideration of the safety measures associated
with such a system.
In addition, TRL is grateful to all the wheelchair manufacturers,
wheelchair tie-down and occupant restraint system manufacturers,
vehicle converters, transport service operators, wheelchair services and
charities that assisted during the project.
145
References
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services for disabled children and their families. London: Audit
Commission.
Department for Transport (2007). Road casualties Great Britain 2006.
London: The Stationery Office.
http://www.dft.gov.uk/162259/162469/221412/221549/227755/rcgb2006
v1.pdf
Disability Rights Commission (2005). Provision and use of transport
vehicles - statutory code of practice - supplement to part 3 code of
practice. Stratford-upon-Avon: Disability Rights Commission.
Eppinger R, Sun E, Kuppa S and Saul R (2000). Supplement:
development of improved injury criteria for the assessment of advanced
automotive restraint systems II. Washington DC: National Highway
Traffic Safety Administration, US Department of Transportation.
Forinton K and Glyn-Davies P (2004). Seat belt load comparison
between ISO 10542 type rig and vehicle tests. Millbrook Report No.
04/0220.
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Hitchcock D, Hussey M, Burchill S and Galley M (2006). A survey of
occupied wheelchairs and scooters conducted in 2005. Leicestershire:
CEDS.
Hitchcock D (2008). Personal communication.
Le Claire M, Visvikis C, Oakley C, Savill T, Edwards M and
Cakebread R (2003). The safety of wheelchair occupants in road
passenger vehicles. Wokingham: TRL.
Lynch, A (2003). Presentation given to GRSG (ad-hoc) group. Informal
document No. 9. 85th GRSG, 21 - 24 October 2003 agenda item 3.
http://www.unece.org/trans/doc/2003/wp29grsg/TRANS-WP29-GRSG85-inf09e.pdf
Mertz H J, Irwin A L and Prasad P (2003). Biomechanical and scaling
bases for frontal and side impact injury assessment reference values.
Proceedings of the 47th Stapp Car Crash Conference, San Diego,
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California, October 2003. Warrendale, PA: Society of Automotive
Engineers, pp. 155-188
National Statistics (2007). Population estimates.
http://www.statistics.gov.uk/cci/nugget.asp?id=6
SMMT (2007). Motor industry facts – 2007.
http://www.smmt.co.uk/publications/publication.cfm?publicationid=15288
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Bibliography
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buses for people with reduced mobility: final scientific report. Brussels:
ESF COST Office.
Medical Devices Agency (2001). Guidance on the safe transportation
of wheelchairs. MHRA device bulletin, DB 2001(03). London: Medical
Devices Agency.
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148
Appendix A. Literature and information review
A.1 Introduction
A literature review was carried out to establish the relevance of any
previous research in this area. The review comprised published
research from the UK and abroad and any other information that it was
possible to obtain.
TRL recognised that a review of this nature would highlight what was
known about the safety of children in wheelchairs from a science and
engineering point of view. It would also highlight any gaps in the
knowledge that should be addressed in the project. However, TRL was
concerned that the review contained the requirements of end users:
children, parents and transport operators. To give a feel for these
practical issues, the literature review was extended to gather relevant
information and experiences from other organisations.
A.2 Legislation and policy background
A.2.1 All children
A.2.1.1
Introduction
Road vehicles are subject to comprehensive regulation. The
requirements cover both the construction of the vehicle and the use of
the safety systems by the occupants. This section provides an overview
of the legislation with respect to children.
The Road Traffic Act 1988 is the relevant legislation in the UK and sets
out the requirements in law. For instance, under Section 15 of the Act, it
is an offence to drive a vehicle with a child under 14 years of age in a
front or rear seat if they are not using the appropriate seat belt or child
restraint. Detailed requirements about the type of seat belt or child
restraint are given in a series of Regulations. Different provision is made
depending on the age and/or height of the child. Also, various
exemptions are made by vehicle class and the circumstances in which
they operate. The key Regulations are the Motor Vehicles (Wearing of
Seat Belts by Children in Front Seats) (Amendment) Regulations 2006
(SI 2006 No. 2213) and the Motor Vehicles (Wearing of Seat Belts)
(Amendment) Regulations 2006 (SI 2006 No. 1892). These Regulations
implement certain provisions of Directive 2003/20/EC (which amends
149
Council Directive 91/671/EEC relating to the compulsory use of safety
belts in vehicles with a gross weight of less than 3.5 tonnes).
The requirements related to the provision of safety equipment within a
vehicle are set out in the Road Vehicles (Construction and Use)
Regulations 1986 (SI 1986 No. 1078). In fact, the approval of most
vehicles is now based around the European Commission Whole Vehicle
Type Approval (ECWVTA) system. The basic concept is that a
production sample is tested and if it passes the tests and the production
methods pass an inspection, vehicles of the same type are approved for
production and sale within Europe. A framework Directive lists a series
of separate technical Directives that the vehicle must be approved to. In
order to gain ECWVTA, a vehicle has to meet the requirements of each
of the relevant individual Directives. The scheme was introduced in the
1970s through Directive 70/156/EEC. A recast new framework Directive
2007/46/EC has now been published and extends the scheme to all
vehicle categories and includes provisions for wheelchair accessible
vehicles.
The technical Directives on vehicle construction cover a range of safety
systems including seats, seat belts and their anchorages. The
performance of child restraint systems is assessed separately through
UNECE Regulation 44.03 or later. Child restraints that meet the
requirements of the Regulation are marked with a label (showing ‘E#’
and ‘44.03’ or ‘.03’) and the group number or weight range of the child
for which it is designed. These restraints can then be sold anywhere
within Europe.
The following sections summarise the requirements for each M category
vehicle.
A.2.1.2
M1 vehicles
The law regarding restraint use by children in M1 vehicles depends on
their age and their height. Children up to three must use a correct child
restraint system in the front seat. A correct child restraint must be used
in the rear also; however, if one is unavailable in a taxi or an emergency
vehicle, the child may travel unrestrained.
Children between three and 11 and less than 135 cm must use a correct
child restraint in the front seat. They must also use a correct child
restraint in the rear seat, provided there is an adult belt; however, there
are three exemptions. The first exemption is travelling in a taxi, the
second is travelling over a short distance of unexpected necessity and
150
the final exemption is where there are two occupied child restraints in
the rear which prevents a third being fitted. In these circumstances, the
adult seat belt must be used.
Children aged 12 and 13 or younger children over 135 cm must use
either an appropriate child restraint or else an adult seat belt in the front
and the rear.
The vehicle construction requirements for seats, seat belts and their
anchorages in M1 vehicles are complex and depend on the age of the
vehicle and the seating position. In general, the majority of M1 vehicles
on the road, including taxis, go beyond the minimum legal requirement
and are fitted with three point seat belts throughout the vehicle. The
technical Directives include performance requirements which are usually
assessed by static pull tests or dynamic tests with crash test dummies.
A.2.1.3
M2 vehicles
Once again, the law on restraint use depends on the age of the child and
their seating position. For instance, children up to three must use a
correct child restraint system in the front seat. A correct child restraint
must be used in the rear also, but only if one is available.
Children between three and 11 and less than 135 cm must use a correct
child restraint in the front seat if one is available; if not, an adult seat belt
must be used. The same rule applies in the rear of M2 vehicles,
although this applies only if a seat belt is fitted in the vehicle.
Children aged 12 and 13 (and those under 12, but 135 cm or more in
height) must use either appropriate child restraints or else an adult seat
belt in the front and the rear. These rules apply to M2 vehicles under 3.5
tonnes. Vehicles above this weight are effectively grouped with M3
vehicles in the Regulations.
The vehicle construction requirements for seats, seat belts and their
anchorages in M2 vehicles are similarly complex and depend on the age
of the vehicle and the seating position. Most M2 vehicles on the road
are now fitted with three point seat belts throughout the vehicle. The
technical Directives include performance requirements which are usually
assessed by static pull tests.
A.2.1.4
M3 vehicles
The law on restraint use by children in M3 vehicles depends on the type
of vehicle. Large buses running scheduled local services in built up
151
areas and on which standing is permitted are exempt from the
requirements for children to wear seat belts and/or use child restraints.
In other buses and coaches, the requirement to use a child restraint or
seat belt in the front seat generally applies; however, there are very few
cases where this would apply since relatively few vehicles are fitted with
front seats.
There are currently no statutory requirements for children under 14 to
wear seat belts or child restraints in the rear seats. European
Commission Directive 2003/20/EC requires children aged three years
and above to use the seat belts where they are fitted in a bus/coach.
However, the UK deferred implementation of the Directive for children
under 14 due to the difficulties in identifying who should be responsible
for ensuring they are restrained. At the time of writing, the DfT was
planning further consultation on how to implement the Directive in a
practical way (DfT, 2007).
Inertia reel seat belts or retractable lap belts are required to be fitted in
all forward and rearward facing seats in M3 vehicles. Lap belts may only
be fitted in forward facing non-exposed seats where an appropriate
energy absorbing seat or surface is present in front. The technical
Directives include performance requirements which are usually
assessed by static pull tests.
A.2.2 Children in wheelchairs
A.2.2.1
Introduction
The Disability Discrimination Act 2005 enabled the Government to lift the
exemption of certain vehicles from Part 3 of the 1995 Act. This is the
part of the Act that deals with access to goods, facilities, services and
premises. The Disability Discrimination (Transport Vehicles)
Regulations 2005 (SI 2005 No. 3190) were made under this power and
came into force from 4th December 2006. With rights of access
improving for wheelchair users, this section provides an overview of the
safety related legislation with respect to children in wheelchairs.
The legislation on restraint use described in the previous section does
not apply to children in wheelchairs. For instance, there are no
requirements in UK law for children in wheelchairs to wear a restraint
system. However, the general safety requirements in Regulation 100 of
the Road Vehicles (Construction and Use) Regulations 1986 (SI 1986
No. 1078) and in Section 40A of the Road Traffic Act 1991 are often
152
mentioned. These require that vehicles are maintained and used in a
way that does not pose a danger or nuisance to any person in the
vehicle or on the road.
Requirements for the safe transport of children in wheelchairs can also
be derived from health and safety legislation. Section 3 of the Health
and Safety at Work Act 1974 places a duty on employers (so far as is
reasonably practical) not to expose a non-employee to a risk to their
health and safety arising from the action of the employer. Section 7 of
the Act places a duty on the employees to take reasonable care for the
safety of anyone who may be affected by his actions or omissions.
Provisions for a wheelchair space and a restraint system are made
within the ECWVTA scheme, which has recently been extended to all M
category vehicles by Directive 2007/46/EC, and within Regulations
passed under Part 5 of the Disability Discrimination Act 1995. For
example, technical requirements for some M category vehicles are
covered by the Public Service Vehicles Accessibility Regulations 2000
(SI 2000 No. 1970; as amended).
Wheelchairs are subject to the Consumer Protection Act 1987. This
gave Ministers the power to make the Medical Device Regulations 1994
(SI 1994 No 3017; as amended). As part of their CE marking process
(which indicates that one or more of the procedures referred to in the
Regulations have been followed), manufacturers of wheelchairs are
required to consider the risks associated with the usage of their
products. For the transportation elements of their risk management,
many wheelchair and seating manufacturers carry out dynamic sled
tests according to the relevant International Standard, such as ISO
7176-19:2001.
The following sections summarise the particular requirements for each M
category vehicle.
A.2.2.2
M1 vehicles
Part 5 of the Disability Discrimination Act 1995 allows the Government to
make accessibility regulations for taxis. The ergonomics of taxi design
for people with disabilities has been examined and full scale evaluation
trials have been carried out. The research established that the floor
height, door height and internal space (floor and head room) of current
purpose built or adapted taxis represent significant barriers to
accessibility (Richardson and Yelding, 2004). The work to develop
proposals for taxis is ongoing, but in the meantime, all licensed taxis in
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London have had to be wheelchair accessible from January 2000. Also,
outside London, some local authorities will give new licences only to
taxis that can carry passengers who remain seated in their wheelchairs.
While this has led to increasing numbers of wheelchair accessible taxis
on the road, the type and performance of the equipment within the
vehicle was largely unregulated. However, the new framework Directive
2007/46/EC includes provisions for special purpose vehicles within the
ECWVTA scheme. This extends to wheelchair accessible vehicles,
which are defined as vehicles within the M1 category constructed or
converted specifically to accommodate one or more persons seated in
their wheelchair. For type approval to be granted, the vehicle
manufacturer or converter will have to demonstrate compliance with a
series of individual technical Directives. These include Directives on the
seats, seat belts and seat belt anchorages. A wheelchair location is
considered a seating position in the framework Directive and must be
equipped with a wheelchair tie-down and occupant restraint system that
meets the requirements of the same technical Directives as any other
seating position as well as the requirements of ISO 10542-1:2001. This
is also the case for the anchorages of the restraint system.
The proposals for taxis and the Directive 2007/46/EC have gone some
way to ensure that accessible M1 vehicles are equipped with the
hardware necessary to transport wheelchair seated passengers with a
degree of protection. However, no special provisions are made for
children; hence the geometry of the restraint may not be suited to their
anatomy.
A.2.2.3
M2 vehicles
Until recently, there were relatively few regulations governing wheelchair
use and safety in M2 vehicles, for adults or children. However, the
ECWVTA scheme has now been extended to cover M2 vehicles by
framework Directive 2007/46/EC. The individual technical Directives
cited in the framework Directive include Directive 2001/85/EC. This
prescribes technical requirements for a wheelchair space and restraint
system in buses and coaches including M2 vehicles. Once again, no
special provisions are made for children.
The Public Service Vehicles Accessibility Regulations 2000 (SI 2000 No.
1970; as amended) apply to vehicles that carry more than 22
passengers on local or scheduled services.
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A.2.2.4
M3 vehicles
A public service vehicle carrying more than 22 passengers is likely to fall
within the M3 category and is therefore subject to the Public Service
Vehicles Accessibility Regulations 2000 (SI 2000 No 1970; as
amended). The Regulations include technical requirements for boarding
aids, for access from the door to a designated wheelchair space and for
the restraint of the wheelchair and user. In urban buses, the wheelchair
faces rearwards against a padded backrest and adjacent to a device
such as a fixed stanchion to stop the wheelchair swinging into the
gangway. In coaches, the wheelchair faces forwards and must be
restrained by a tie-down system and the occupant must be provided with
a seat belt. Relevant performance tests are included or referenced for
the equipment but there are no specific requirements for children.
As mentioned above, the ECWVTA scheme has now been extended to
cover M3 vehicles by framework Directive 2007/46/EC. The individual
technical Directives cited in the framework Directive include Directive
2001/85/EC. This prescribes technical requirements for a wheelchair
space and restraint system in buses and coaches including M3 vehicles.
Once again, no special provisions are made for children.
A.3 Biomechanics of children
A.3.1 All children
A.3.1.1
Introduction
The purpose of a restraint system is threefold. Firstly, it must minimise
the risk of ejection from the vehicle. Secondly, it must minimise the risk
of body contact with the interior of the vehicle. Thirdly, it must absorb
and distribute the impact forces over the strongest parts of the body.
The three point seat belt is the main type of restraint system in road
vehicles. It has been fundamental to the protection of adults since it
became compulsory to wear one (in the front seat) in 1983. The
Government estimates that seat belts have reduced minor casualties by
1,590,000, serious casualties by 590,000 and deaths by 50,000
(www.thinkseatbelts.com).
It is well known that although seat belts provide a high level of protection
for adults, children cannot achieve the correct placement and fit of the
belt. Furthermore, in the case of young children, it is necessary to apply
the restraint forces over different areas of the body. An appreciation of
the anatomy, growth and development of children has been critical to the
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design of effective child restraint systems. Children require special
attention because their tissues have different biomechanical properties
compared with adults. Furthermore, their needs from a restraint system
change as they grow.
There are three stages of development before adulthood is reached.
Infancy is the first stage and refers to the period from birth to 18 months.
The second stage is childhood and ranges from 18 months to 12 years
and includes toddlers (18 months to four years) and primary school aged
children (four to 12 years). The final stage is adolescence and is usually
considered to begin around the age of 13 years. Most children are tall
enough to use the adult seat belt safely by this stage. The following
sections examine the anatomy and physiology of children during infancy
and childhood, focusing on the implications for their protection in a
collision.
A.3.1.2
Infancy
The skull of an infant is a series of broadly spaced elastic bones. The
spaces between the bones are called fontanels and allow the skull to
change size and shape during birth and permit rapid brain growth during
infancy. The fontanels are gradually replaced by bone until they become
sutures. The largest of the fontanels, along the midline of the skull
closes around 18 - 24 months after birth (Tortora and Gabrowski, 1996).
The presence of the fontanels and the thickness of the bone mean that
an infant’s skull is relatively flexible; hence low levels of impact loading
can result in significant deformation of the skull and brain. Another
important feature of the skull during infancy is its size and weight in
relation to the rest of the body. This, combined with developing neck
structures, is thought to be involved in some neck injury mechanisms
(Fuchs et al., 1989).
The flexibility of the spine is also important. In fact, immature spines are
much more flexible than relative size alone would predict (Kumaresan et
al., 2000 referenced from Weber, 2000). This is due, in part, to the
ligaments, which are flexible to accommodate growth. The key point
from the literature is that the spinal column and ligaments of infants are
relatively elastic allowing elongation of up to two inches (50.8 mm),
whereas the spinal cord ruptures if stretched more than ¼ inch (6.35
mm) (Leventhal, 1960 referenced from Huelke, 1998). For these
reasons, it is important that a restraint system for infants prevents
motion of their head with respect to their torso.
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Adult restraint systems such as three point seat belts apply some of the
restraint forces to the chest. This is inappropriate for infants because
the skeletal system is still developing from cartilage and therefore
maintains a high degree of flexibility. As a result, loading to an infant’s
chest from a seat belt or harness would lead to deformation of the chest
wall onto the thoracic organs. Similarly, seat belts are designed to
engage with the pelvis, but an infant’s pelvis is relatively small and
unstable. It would be unable to withstand the loading from a belt or
harness. Furthermore, blunt trauma to the abdomen would be injurious
because the muscle wall is undeveloped with little or no skeletal
protection. The liver is particularly at risk because it occupies two-fifths
of the abdominal cavity in infants and is not protected by the rib cage
(Sturtz, 1980; Huelke, 1998).
As a result of these developmental issues, infants must use a rear facing
child restraint system. These devices distribute the impact forces over
the strongest and widest area possible: the infant’s back. They have
proven very effective in protecting young children in vehicle collisions
although their performance is sometimes reduced by misuse.
A.3.1.3
Childhood
The fontanels have closed by the time childhood is reached; however,
the thickness and composition of a child’s skull is different from an
adult’s. The process of forming bone (called ossification) is not
completed until the age of six or seven years and throughout childhood
the stiffness of the skull is less than that of an adult (Sturz, 1980). It is
important, therefore, that a child restraint system limits forward, vertical
and rearward head excursion.
During childhood, the muscles and ligaments in the spinal column
strengthen, the bones reach a mature shape and size and areas of
cartilage are replaced by normal bone (Yoganandan et al., 1999). Most
researchers agree, therefore, that if necessary, children may face
forwards in a car from the age of one year (Bull and Sheese, 2000).
Nevertheless, parents are encouraged to keep children rear facing for as
long as possible. In the UK, the advice is that a child can travel forward
facing only if they have exceeded the maximum weight for their seat
(typically 13 kg) or their head is higher than the top of their seat, or their
seated height is too tall for the harness (www.thinkroadsafety.gov.uk).
The chest increases in width and depth during childhood and a process
of elongation occurs. This raises the child’s seated height and affects
the fit of the restraint system. Child restraints include some means of
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adjusting the shoulder straps or belt to accommodate these changes.
The rib cage grows downwards during childhood to provide some
protection to the liver, spleen and kidneys (Huelke, 1998). Normal
calcified bone replaces the cartilage in the ribs and hence their strength
increases, although they remain somewhat flexible. Similarly, the pelvis
grows larger and offers greater protection to some abdominal organs
such as the bladder. However, the key development in the pelvis, the
formation of the superior anterior iliac spines, is not complete until at
least ten years of age. With a small, underdeveloped pelvis, there is a
risk that the lap part of the seat belt can slip off during a crash and
penetrate the abdomen.
Although a number of developmental changes have taken place by
childhood, the protection of the head remains the priority. It is critical,
therefore, that contact with the interior of the vehicle is prevented. The
risk of neck injury due to inertial loading from the head is reduced in
childhood because the muscles and ligaments are stronger. As a result,
children are able to travel forward facing with relatively low risk of
serious neck injury if head contact is prevented. Nevertheless, the way
the child is secured in the child restraint is important for the protection of
the chest and abdomen. In early childhood (until approximately four
years), the ribs and pelvis are relatively small and somewhat flexible so
a child restraint with an integral harness is used to reduce the risk of
restraint induced injury. The harness must include a fifth point or crotch
strap to keep the lap straps on the pelvis and prevent submarining. In
later childhood (from approximately four years), when a child has
outgrown the harness or exceeded the weight limit for their seat, a
booster seat is used. This lifts the child’s seating position to produce a
more favourable interaction with the adult belt geometry. Booster seats
include two sets of guides. The lower guides ensure the lap part of the
seat belt passes over the top of the thighs. These guides also keep the
lower part of the diagonal belt adjacent to the pelvis. The upper guide
ensures that the upper part of the diagonal belt lies flat on the centre of
the shoulder and therefore crosses the centre of the chest. A booster
seat is necessary throughout childhood because the pelvis has not
developed fully and the child’s seated height is likely to be too low for an
adult seat belt.
A.3.2 Children in wheelchairs
A.3.2.1
Introduction
A child that uses a wheelchair is subject to the same fundamental
changes in their physical development as any other child. Furthermore,
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their basic needs from a restraint system are likely to be similar. There
may, however, be additional issues to consider. For instance, it would
be useful to understand how children in wheelchairs compare with the
average population of children in terms of their anthropometry. This
information would help to inform discussions about the use of child
dummies to represent child wheelchair users. It would also be useful to
understand whether children in wheelchairs have any additional needs
and how these might be accommodated. This section provides an
overview of the literature that was found to be relevant to these issues.
A.3.2.2
Anthropometry
The Office of Population Census and Surveys (OPCS) completed four
large national surveys of disability between 1985 and 1988. The
Department of Health and Social Security (DHSS) requested the surveys
to provide up to date information about the number, characteristics and
circumstances of disabled adults and children in the UK for the purposes
of planning benefits and services. Although a great deal of information
was compiled following the surveys, it did not include any information
about the fundamental anthropometry of children in wheelchairs. In fact,
there is a lack of accurate data available to establish the total number of
disabled children in Britain, the nature of their disabilities and the range
of needs arising from their disabilities (Research in Practice, 2005;
Hutchison and Gordon, 2004).
One study examined the height, weight and prevalence of feeding
problems among disabled children. This concluded that feeding
problems contribute to short stature and low weight in severely disabled
children (Thommessen et al., 1991). Similar research has looked at the
risk of undernutrition and the pattern of growth for children with cerebral
palsy (Hung et al., 2003; Krick et al., 1996). However, it was not
possible to find clear, detailed information in the literature about the
characteristics of children in wheelchairs. There are a wide variety of
medical conditions that can lead to temporary or permanent wheelchair
use by children. It seems likely that the anthropometry of children in
wheelchairs will be different depending on their condition. TRL was able
to examine some anonymous height and weight data provided by a UK
charity. The sample was too small for scientific analysis and was biased
by the children’s medical conditions. Nevertheless, it suggested that
children in wheelchairs tend to be smaller for a given age than the
average population, which child dummies represent.
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A.3.2.3
Additional needs
Many children in wheelchairs use supportive seating systems for
postural management. Generally, this seating is intended to prevent
problems that can result from uneven weight bearing or from the inability
to move out of poor positions (Disabled Living Foundation, 2003). A
number of different approaches are taken by manufacturers of these
systems. Some systems try to achieve a symmetrical and balanced
sitting posture with a neutral alignment of the spine (Active Design,
2003). They aim to prevent unwanted movement, while allowing
movement within safe boundaries. They also provide a stable base of
support to allow head and arm movement without loss of balance.
Often a positioning belt or harness is incorporated into the seat;
however, these are rarely crash tested. As a result, the child needs to
wear an additional restraint during transport. This can lead to children
travelling with several straps across their chest, possibly affecting the fit
of the main crash tested restraint. In addition, the structure of the
seating system with its pads and inserts may also interfere with the seat
belt. These could be important issues given the capacity of the torso to
bear loads during childhood.
A.4 Current practices
A.4.1 Introduction
Governments and researchers can benefit from an understanding of the
real world issues and the concerns of all interested parties.
Thornthwaite and Pettitt (1993) examined current school transport
practice in the UK and USA, but more up to date information is required.
The information in this section was compiled following discussions with
mobility centres, transport operators, local authorities, charities and
following observations of wheelchair transportation at a special school.
It was not intended to be a scientific study, but instead provides a useful
insight into the current situation in M category vehicles.
A.4.2 M1 vehicles
Wheelchair accessible M1 vehicles are very convenient for parents of
children in wheelchairs and offer something approaching the freedom to
travel that many people enjoy. However, these vehicles are expensive
to buy or to lease, although grants are sometimes available. As a result,
many parents maintain a conventional vehicle and transfer their child to
a child restraint, or to a vehicle seat, before a journey. A child is likely to
receive better protection in the event of a collision from travelling in this
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way and there are special needs child restraint systems available.
Nevertheless, many parents arrive at mobility centres with back
problems through lifting their child into their vehicle. It is a particularly
difficult movement, which involves twisting and stooping with a child in
their arms who is unable to assist or who may spasm. This process can
continue into adolescence, depending on the ability or health of the
parent. It would appear from discussions with mobility centre staff that
parents would appreciate more advice about transporting children with
special needs, including when a child should travel in their wheelchair.
Taxis are sometimes used by parents of children in wheelchairs, but
there can be a wide variation in the quality of the vehicle, the awareness
of the driver of safety issues and also in their helpfulness.
Manufacturers of taxis include training on the use of wheelchair tie-down
and occupant restraints as part of the vehicle hand-over process;
however, there is a large second-hand market and it is possible,
therefore, that some drivers are not receiving this training.
A.4.3 M2 vehicles
M2 vehicles are used widely for community transport and for taking
children to school. In fact, a child may start to travel in their wheelchair
for the first time when they reach school age. This is because it is not
always practical to transfer every child in a wheelchair to a vehicle seat.
Although different policies are in place, some operators prefer not to
transfer children due to manual handling issues or due to parents’
sensitivities. However, it should be noted that the Manual Handling
Operations Regulations 1992 (SI 1992 No. 2793) do not prevent
transport operators from lifting children into a vehicle seat. Instead, they
place a requirement on the employer to assess the situation, reduce the
risk of injury and provide information to employees.
Community transport differs from public transport in that the operators
know who will be using their service on each trip. Special provisions can
therefore be made to meet each individual’s needs. This usually means
that there is a risk management process for each child, with some
transport operators adopting a passport system to compile all the
necessary information. This would typically include details of the
equipment needed to restrain the child and their wheelchair. Diligent
transport operators are putting these systems in place to ensure that
children in wheelchairs are accommodated in vehicles with the correct
equipment for their wheelchairs. However, a child on a school or
community bus would not usually be subject to an individual risk
assessment or required to have a ‘passport’. Effective standardisation
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should remove the necessity for such tailored solutions because all
wheelchair tie-down and occupant restraint systems would be
compatible with all wheelchairs.
There are several wheelchair tie-down and occupant restraint systems
on the market; however, wheelchair manufacturers tend to recommend
only one or two systems for use with their wheelchairs. It is important,
therefore, for transport operators to be able to identify the make and
model of the wheelchair in order to use the correct equipment. This can
prove difficult if the wheelchair instructions are lost or if the labelling on
the wheelchair has worn away.
Ideally, every wheelchair that is intended for use on a vehicle would be
fitted with clearly marked attachment points for a wheelchair tie-down
and occupant restraint system. Stickers on the wheelchair frame are
currently used on some wheelchairs, but these can be difficult to find
and can be positioned inconsistently. Instead, a system of colour coding
could be used to assist transport operators in finding the correct
attachment point. In addition, the attachment points could be designed
in such a way to be compatible with any wheelchair tie-down and
occupant restraint system, irrespective of the manufacturer. This would
lead to a universal system whereby any combination of wheelchair and
wheelchair tie-down and occupant restraint system could be used. This
is addressed to some extent by ISO 7176-19:2001; however, it would
appear that the Standard is not always implemented fully.
Community transport operators face a number of additional challenges.
For example, the children may have behavioural issues and not want to
be restrained. In addition, the drivers and their escorts need to monitor
all the children in the vehicle, which may include ambulant children,
while the wheelchair users are being restrained. It is important,
therefore, that the wheelchair tie-down and occupant restraints are easy
to use and can be fitted quickly. It seems likely that any efforts to bring
transport operators, wheelchair manufacturers and restraint system
manufacturers together would be beneficial.
TRL’s observations suggest that there could, once again, be a wide
variation in the standard of vehicles and restraint systems in use.
Furthermore, few vehicles appear to be fitted with an upper anchorage
point for the diagonal part of the seat belt. Anecdotally, vehicles have
been reported as old and frequently unreliable with restraint equipment,
in some cases, that is in a poor state of repair. Concerns have also
been expressed about the level of staff training and frequent staff
changes. However, it is often the case that good practice is unreported;
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hence it is inappropriate to draw firm conclusions from these
observations. A survey of vehicles, equipment and training would be a
useful way of establishing the current situation.
A.4.4 M3 vehicles
The Public Service Vehicles Accessibility Regulations 2000 (SI 2000
No.1970; as amended) have led to increasing numbers of buses that
provide access for wheelchair users and a designated wheelchair space.
Nevertheless, the following comment was made by a parent in a report
by the Audit Commission (2003):
I know they do have those low floor buses but round here it’s touch and
go whether you get one, or if there is one then there’s already a buggy
on there. The Saturday before, we didn’t get home until eight o’clock in
the evening because I waited two hours for a bus.
It seems likely that the situation will have improved since the time of the
Audit Commission report; however, parents may still find these services
difficult to use. Many buses in urban areas are busy at peak times and
hence the gangway and wheelchair space might be occupied by other
passengers. While signs in buses make it clear that the space is for
wheelchair users, it is not clear to what extent this would be enforced by
drivers or adhered to by other passengers. In addition, parents of
children in wheelchairs can have a number of items to carry such as
specialist foods or changing pads and may have other children
accompanying them. Clearly, an accessible bus service will not meet
everyone’s needs, but there are limits to what is practicable and it would
appear that the latest vehicles offer a good service within these limits.
A.5 Performance of children’s wheelchairs and restraint systems
A.5.1 Accident studies
It is important to monitor the performance of vehicle safety equipment in
real accidents. For a given type of accident or scenario, vehicle safety
researchers would typically seek to discover which areas of the body are
being injured and what the contributing factors are. This information
helps policy makers to identify priorities for regulation.
It is well known that, traditionally, there has been very little information
available on the performance of wheelchairs and their restraint systems
in real accidents. One of the challenges is that the accident databases
used for such research are not detailed enough to identify passengers
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seated in a wheelchair. One such database is STATS19, a national
road accident database named after the code number of the collection
form. Road accidents in the UK that involve personal injury are recorded
using the STATS19 collection system if they are reported to the police
within 30 days. The form comprises a brief record of the accident
location, the vehicles involved and the casualties, but it does not provide
any detail such as the use of a restraint system. Nevertheless,
STATS19 is a useful way of identifying accidents involving particular
vehicles or occupant groups. More detailed reports of each accident
may then be obtained from other sources. This approach was taken by
TRL in a previous project for the DfT (PPAD 9/72/106). The findings
were reported by Webster (2006). STATS19 was used to identify singlevehicle accidents involving a bus, a coach or a minibus, where
pedestrians were not involved. Each accident and casualty was
investigated further to obtain information about the activity of the
passengers and use of a wheelchair or other mobility aid. This
information was obtained from the relevant police force or local authority.
Single-vehicle accidents were selected by Webster (2006) because this
met the needs of the project (PPAD 9/72/106). However, most collisions
involve another vehicle or vehicles. Single-vehicle collisions are much
less common. As a result, there were no collisions in the accident data
presented by Webster (2006). Instead, the accidents occurred during
boarding and alighting, braking or normal manoeuvring. Several of
these cases involved injury to wheelchair users while their vehicle was in
motion, but restraint systems were not used or they were used
incorrectly. For example, a 12 year old child was injured because their
wheelchair restraint ‘gave way’ when the vehicle braked. The child
received a number of fractures, although it was known that he had a
brittle bone condition.
Other studies investigating injuries to wheelchair users make similar
observations. For example, Richardson (1991) examined accident data
from the National Electronic Injury Surveillance System (NEISS) in the
USA. Based on the sample, Richardson (1991) estimated that there
were around 2,200 injuries nationwide among wheelchair users in motor
vehicles from 1986 to 1990. However, most of the injuries were
attributed to improper restraint during sudden braking or sharp turns.
Children were not identified in the study. Shaw (2000) made a similar
analysis of the NEISS database for 1988 to 1996 and estimated that
there were around 1,320 injuries nationwide. Once again, injuries were
attributed to abrupt vehicle manoeuvres. Frost and Bertocci (2006)
carried out a retrospective study of wheelchair related incident reports
from a metropolitan area in the USA between 2002 and 2005. The study
focused on large, public transport buses and found that the majority of
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incidents (73.2 percent) occurred when the bus was stationary. Of the
incidents that occurred when the bus was in motion, most occurred in
normal driving (72.7 percent) while the remainder occurred in
emergency manoeuvres. There were no incidents involving a bus crash
and there was no reference to children.
Although these studies did not identify any vehicle collisions, they
highlight the need for appropriate restraint for passengers seated in
wheelchairs. It is of some concern that despite the availability of such
equipment, wheelchair users were injured in normal driving or
emergency manoeuvres. These studies provide no information about
the performance of appropriate equipment when it is used correctly in a
collision. In fact, only one study was found that included detailed case
reports featuring wheelchair seated occupants and these were adults.
Schneider et al. (2003) described two real world accident cases; in one
case, a 28 year old passenger in the rear of a minivan was injured
during a moderate 20 mph collision. His electric wheelchair was
restrained well by a four point tie-down system that was compliant with
SAE J2249:1996. However, he was not wearing a seat belt and was
injured after the postural belt he was wearing failed. In the other case, a
passenger in a manual wheelchair was ejected from the vehicle during a
roll-over. The driver of the vehicle had reported that the wheelchair user
was restrained with a four point wheelchair tie-down and a three point
seat belt that were both compliant with SAE J2249:1996. Following an
investigation, Schneider et al. (2003) concluded that the seat belt buckle
released after contacting the wheel rim during the impact. The occupant
was thrown through a side window fracturing their legs on contact with
the ground outside the vehicle while the wheelchair remained in place.
In an effort to obtain more information, the Cooperative Crash Injury
Study (CCIS) database was examined by TRL. The CCIS is a
collaborative project to investigate and document accidents in the UK.
The project is managed by TRL on behalf of the DfT and a number of
vehicle manufacturers that also support the study. Investigation teams
monitor the details of all injury accidents that are reported within their
limited geographical areas. From these accidents, cases are selected
for possible inclusion in the study based on a number of strict criteria.
There were 13,835 occupants in the database at the time of the
investigation; however, only one child was found with special needs and
she was not a wheelchair user. A search of the internet found an
accident involving a minibus carrying children to a special needs school
in Ireland. Two children were killed; however, reports of the accident did
not state whether any children were wheelchair users (BBC News,
1998).
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A.5.2 Laboratory tests and simulations
The safety of passengers who remain seated in a wheelchair has
interested governments and researchers since the late 1970s. However,
in the absence of detailed accident information, researchers have been
limited to the use of laboratory sled testing and computer simulation to
draw conclusions about the safety of wheelchair occupants. Studies
from this period highlighted three broad, but now well-established
principles:
•
The wheelchair must be restrained and there must also be a means
of protecting the occupant (Rider et al., 1976).
•
Wheelchairs are not just mobility aids; they must be capable of
withstanding the forces in a crash (Kallieris et al., 1981).
•
Wheelchair users should not travel facing sideways in a vehicle
(Schneider and Melvin, 1978).
Most physical testing and computer simulations carried out to date have
used 50th percentile male dummies. There is much less research
focusing on children in wheelchairs. Nevertheless, several early studies
examined the crashworthiness of wheelchairs and restraint systems for
disabled children (Schneider et al., 1979; Khadilkar and Will, 1980;
Seeger and Caudrey, 1983; Benson and Schneider, 1984). However,
examining these studies in depth reveals that children’s wheelchairs
have changed considerably since that time.
More recently, Colvin et al. (1999) investigated some products intended
to improve the protection afforded to children. These included a support
strap to improve the connection between a wheelchair and a seating
system, a wheelchair integrated lap belt, a wheelchair integrated upper
torso restraint and a prototype garment to provide support and comfort
to wheelchair users. Unfortunately, no test results were presented and
the conclusions of the study were limited.
In another study, Ha et al. (2004a) developed and validated a six year
old wheelchair seated occupant model in MADYMO for use in their
research studies. The model comprised a Hybrid III six year old dummy
seated in a common manual wheelchair from the USA. It was
subsequently used to investigate the forces acting on a wheelchair
during a 20 g/48 kph front impact (Ha et al., 2004b). Forces were
extracted from the model at several locations. A parameter sweep was
then carried out to examine the effect of a number of wheelchair set up
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adjustments on these forces. The authors anticipated that the study
would provide wheelchair and seating manufacturers with an insight into
the magnitude of the forces that would act on their products in a front
impact (of the same severity). It was probably outside the scope of the
paper presented by Ha et al. (2004b); however, it would have been
useful to include the effect of the various wheelchair adjustments on the
dummy excursions and loads in the model.
Three sled tests were carried out to validate the MADYMO model.
These were reported initially by Ha et al. (2004a), but in more detail by
Ha and Bertocci. (2007). In the later study, the dummy accelerations
and forces were compared with performance limits in FMVSS 213 and
FMVSS 208. The chest acceleration was within the limit in FMVSS 213;
however, the results exceeded the Nij limit in FMVSS 208 and were
approaching the chest compression limit. The authors concluded that
children who remain seated in their wheelchair may be at risk of injury,
especially to the neck and chest, but they also noted that concerns had
been raised elsewhere about the biofidelity of the dummy neck.
Baseline tests with a child in a vehicle seat or child restraint were not
carried out in the study, but other authors have noted high Nij values
when the Hybrid III child dummy was seated in a child restraint
(Sherwood et al., 2003). This injury criterion was developed for adults,
but has been scaled for use with children (Eppinger et al., 2000; Mertz et
al., 2003). Although it is often used in research studies in the USA, it
has not been validated for children and should therefore be used with
caution.
The use of wheelchair integrated restraint systems has interested
researchers for several years (Van Roosmalen and Bertocci, 2000; Van
Roosmalen et al., 2001). Much of this interest has focused on adult
dummies in computer models of the surrogate wheelchair. However,
Manary et al. (2006) performed sled tests to examine the feasibility of
integrating a five point harness into a common manual wheelchair. The
Hybrid III three year old dummy was used in the study. The backrest of
the manual wheelchair failed in the first test. This was attributed to the
additional loading from the dummy during the impact. The wheelchair
was strengthened and performed well during the second test. It must be
noted that both wheelchairs were described as ‘previously used’
although no details were provided. A baseline test with a three point
seat belt instead of the harness was not carried out, but the authors
reported that the harness had the potential to improve occupant
protection for small children who remain in their wheelchair. The
ANSI/RESNA WC/19:2001 Standard was the main focus for the analysis
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but some dummy loads were also included. These fell below the
performance limit in FMVSS 213.
The studies described so far have focused on forward facing
wheelchairs in front impact tests. Manary et al. (2007) carried out a
series of rear impact tests with a range of wheelchairs. A Hybrid III 50th
percentile male dummy was used, except in one test, where a Hybrid III
fifth percentile female dummy was used. The test conditions
(25 kph/14 g) were intended to represent a moderate severity rear
impact for a forward facing passenger in a minivan. The wheelchair
backrest failed in most of the tests, resulting in the dummy coming to
rest on the floor of the sled. It was also noted that the front wheelchair
tie-down attachment points failed in a third of the tests, which
contributed to the violent kinematics of the dummy. The study highlights
that rear impact has not been addressed in any way by wheelchair
manufacturers.
Fuhrman et al. (2007) carried out rear impact tests with a Hybrid III six
year old dummy seated in a manual wheelchair. The test conditions
were similar to those used by Manary et al. (2007). Tests were carried
out with and without a headrest attached to the wheelchair. In this
study, the wheelchair withstood the loading from the dummy during the
impact. The headrest was designed for posture only, but appeared to
support the head and neck in these rear impact tests.
A.6 Discussion
Legislation for the protection of occupants in road vehicles can be
divided into three groups. Firstly, there are technical requirements for
the type and specifications of the restraint system in the vehicle.
Secondly, there are technical requirements for the performance of the
restraint system, which are assessed by static pull tests or dynamic
impact tests with dummies. Within this group, children are addressed
specifically by UNECE Regulation 44. Finally, there are requirements to
use a restraint system when travelling in a vehicle. Once again, there
are specific requirements for children.
For wheelchair users, there is an extra dimension, which is access to the
vehicle or to the service provided by the vehicle. This has improved
considerably with the introduction of the Disability Discrimination Act
1995 and the associated Regulations. For children in wheelchairs, the
legislation currently in place (or coming into force) covers the type and
specification of the restraint system in the vehicle. However, the
technical requirements for the performance of the restraint system
168
(including the wheelchair) do not address the protection of children
directly in the way that UNECE Regulation 44 does. In addition, there is
no legislation governing the use of a restraint system by wheelchair
users including children. It could be argued, therefore, that children in
wheelchairs do not receive comparable safeguards in legislation as
other children.
There is a significant amount of research in child biomechanics that can
be drawn on by designers of child restraint systems. This has led to a
number of different solutions that are tailored to the stage in the child’s
growth and development. Decades of research carried out to monitor
the performance of child restraints in real accidents has shown that
children can withstand the forces in a collision when they are restrained
appropriately according to their level of development. Although there
was little or no information on the biomechanical characteristics of
children that use wheelchairs, the same principles for restraint design
should apply.
There is a wide range of equipment on the market to restrain children
and their wheelchairs in vehicles. Manufacturers of this equipment
include instructions about the use of their products in vehicles, but this
can vary in detail and quality. Parents and carers of children in
wheelchairs would probably appreciate, therefore, any advice on the
most appropriate way to restrain their children and when it is safe for
them to travel while seated in their wheelchair.
There are reasonably mature Standards in place that govern both the
design and performance of wheelchairs and wheelchair tie-down and
occupant restraints. Nevertheless, there can be compatibility issues
among devices intended for use on a vehicle. It would appear,
therefore, that these Standards are not being implemented fully. In
addition, more information is needed on the way the Standards are
driving the development of equipment and whether this equipment
meets the needs of children, parents and transport operators.
There is almost no information available about the performance of
wheelchairs and their restraint systems in real accidents. It is possible
that very few accidents have occurred involving a vehicle that is carrying
children in wheelchairs. However, it would be highly beneficial to
develop some means of identifying such cases. For example, STATS19
could be used to identify accidents involving a child passenger in a
minibus, bus or coach. Reports of each accident could then be obtained
from the police, or from other sources, and the involvement of any
wheelchair seated children could be determined. Another approach
169
would be to set up a monitoring system to identify any accidents that
occur in the future. This could take the form of a questionnaire study
similar to that carried out by TRL (for the DfT) to obtain information
about the performance of child restraint systems in accidents (Visvikis
and Le Claire, Child occupant protection – accident analyses, 2003;
unpublished Project Report PR SE/760/03).
There have been relatively few laboratory studies of the safety of
children in wheelchairs in vehicles. The studies carried out to date have,
in most cases, focused on manual wheelchairs with the Hybrid III six
year old dummy to represent a child. Further research is needed to
examine the level of protection afforded to children in a broader range of
wheelchairs. This research should consider the use of dummies to
represent both the smallest and the largest children that use each
wheelchair.
A.7 Conclusions
•
There is no all-encompassing legislation in place to address the
protection of children in wheelchairs in vehicles.
•
Transfer to a rear facing child restraint system is the best solution
for infants.
•
Transfer to a forward facing child restraint is the best solution for
young children.
•
In later childhood, children need to travel in their wheelchair.
•
More information is needed on the number and characteristics of
children in wheelchairs.
•
A significant number of children travel in wheelchairs without
incident.
•
The performance of children’s wheelchairs in real accidents needs
to be understood.
•
The ability of children’s wheelchairs to limit biomechanical loading
needs to be understood.
170
A.8 Recommendations
•
The test programme should examine the safety of children from
three years until 1.35 metres or 12 years of age.
•
Supportive seating is important for postural management and
should be considered in the test programme.
•
All vehicle categories need to be considered in the development of
the test programme.
•
Road traffic legislation should include disabled children.
•
Children’s wheelchairs designed for use in a vehicle should be
treated as child restraint systems and similar limits should be
applied to their use and performance.
•
Clear guidance should be given to parents and transport operators
on the way children must travel at each stage of their development.
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176
Appendix B. Field study of vehicle and wheelchair
interaction
B.1 Introduction
Laboratory studies of wheelchair seated occupant protection are carried
out with a simple representation of the vehicle interior. This is usually
limited to the floor and to the anchorage points of the restraint system.
This approach removes any effects that the design of a specific vehicle
might have on the test results. However, it can result in a test set up
that is somewhat detached from the situation in real vehicles.
The field study was devised to improve our understanding of the way
that children and their wheelchairs interact with real vehicles and
restraint systems. The aim of the study was to identify potential
problems in the orientation of the wheelchair, the location of the vehicle
structures and the geometry of the (wheelchair and occupant) restraint
system. A range of representative wheelchairs and vehicles were used
in the study. In each vehicle, child dummies were seated in the
wheelchairs and restrained using whatever means were provided in the
vehicle. It was recognised that this sometimes differed from the
wheelchair manufacturer’s instructions for transport.
A number of different M category vehicles were examined in the field
study. These were grouped as follows:
•
M1 and M2 vehicles with forward facing wheelchair passengers.
These included both converted small multi-purpose vehicles and
minibuses.
•
M1 and M2 vehicles with rear facing wheelchair passengers. In
fact, no M2 vehicles were found in which a wheelchair user regularly
travels rear facing. The vehicles examined were all M1 vehicles that
were purpose built or specially adapted to function as a taxi.
•
M3 vehicles with forward facing wheelchair passengers. These
were coaches.
•
M3 vehicles with rear facing passengers. These were buses used
on scheduled urban services.
For each group, a number of different vehicles were examined to ensure
that the findings were not influenced by a particular example.
177
Four wheelchairs were used during the field study. The wheelchairs
were selected to represent the many different devices that children use.
The four wheelchairs were:
•
A folding manual wheelchair with a sling canvas seat.
•
A rigid manual wheelchair for active users.
•
An electric wheelchair with a reclining or tilting function.
•
A buggy style wheelchair with a seat comprising a postural
positioning system.
All four wheelchairs were production models loaned to TRL by the
manufacturers. The manual wheelchair, electric wheelchair and buggy
were suitable for use in a vehicle as stated in the product literature. The
active user wheelchair was not suitable for use in a vehicle; however,
this type of wheelchair is popular with some children and may be used in
transport despite the manufacturer’s instructions. The wheelchairs are
shown in Figure B1.
Basic manual wheelchair
Active wheelchair
178
Electric wheelchair
Buggy style wheelchair
Figure B1 Wheelchairs used in the field study
It was understood that these wheelchairs represented a limited cross
section of the devices available for children. However, for the purposes
of the field study, they included a number of key features shared by the
many different designs that are found. It was concluded, therefore, that
the selection of wheelchairs covered the widest range of features
considered to be important for the investigation of wheelchair interaction
with vehicles.
The following sections present the findings of the field study for each of
the four groups described above.
B.2 M1 and M2 forward facing
The field study included several M1 and M2 vehicles in which a
passenger in a wheelchair travels forward facing. Some examples are
shown in Figure B2 and Figure B3. Figure B2 shows the multi-purpose
vehicles used in the study. These were small vehicles defined as M1
according to the system of classification in the European Commission
Directive 2007/46/EC (Annex 2). The vehicle on the left of Figure B2
featured a permanent space for a wheelchair seated passenger and is
an example of the type of vehicle that a parent might purchase or lease
for their private use. It included a four point wheelchair restraint and a
three point seat belt. The seat belt was similar in design to a traditional
automotive belt and included an upper anchorage for the diagonal part
of the belt.
179
The image on the right of Figure B2 shows the other multi-purpose
vehicle used in the study. This vehicle was accessible to wheelchair
users only when the rear seats were folded away and is an example of
the type of vehicle that is sometimes used for private hire. It included an
aftermarket wheelchair tie-down and occupant restraint system (i.e.
supplied separately to the original vehicle) that would be fitted by the
driver. There was no upper anchorage point for the diagonal part of the
seat belt.
Figure B3 shows examples of the minibuses used in the field study.
These were defined as M2 according to the system of classification in
the European Commission Directive 2007/46/EC (Annex 2). All of the
minibuses included a flexible interior layout and were examples of the
type of vehicles that are sometimes used for school or community
transport. A space was reserved for wheelchair users towards the rear
of the vehicles to allow ingress and egress via a lift. Aftermarket
wheelchair tie-down and occupant restraint systems were included, to be
fitted by the driver or the escort. None of the minibuses were fitted with
an upper anchorage point for the diagonal part of the seat belt and it
would appear that such anchorages are rarely found.
M1 vehicle with permanent
wheelchair space
M1 vehicle with flexible wheelchair
space
Figure B2 Passenger compartment in some M1 vehicles
180
M2 vehicle with flexible wheelchair
space
M2 vehicle with flexible wheelchair
space
Figure B3 Passenger compartment in some M2 vehicles
The multi-purpose vehicle with a permanent wheelchair space was fitted
with lap belt anchorages that were relatively wide, to allow access to the
space from the rear and to accommodate a range of wheelchairs and
occupants. This is illustrated in Figure B4. The image on the left shows
the rear view when the electric wheelchair was positioned in the
wheelchair space. The image on the right shows the front view and the
path of the belt around the dummy. The position of the lap part of the
seat belt with respect to the dummy’s pelvis was reasonable with this
arrangement (if not ideal). However, the contact area between the belt
and the pelvis was reduced as a result of the location of the anchorages
in the vehicle on either side of the wheelchair. Clearly, it would be very
difficult to locate these anchorages in the optimum position for every
wheelchair user that might travel in the vehicle.
181
Figure B4 Lap belt anchorage location in an M1 vehicle with a
permanent wheelchair space and the effect on belt path
In M1 and M2 vehicles with a flexible wheelchair space, the anchorages
for the lap part of the seat belt and consequently the seat belt buckle
were attached to the floor tracking behind the wheelchair. As a result, it
was sometimes the case that a gap was created where the diagonal part
of the seat belt would ideally meet with the lap part of the belt. The
diagonal part of the belt passed high across the ribs of the dummy
before joining the lap belt at the buckle behind. This is highlighted in the
image on the left of Figure B5. The image on the right of Figure B5
shows how parts of the wheelchair sometimes obstructed the ideal path
of the seat belt. In this instance, the buggy style wheelchair, with its
support pads, illustrates this issue. It also shows how the positioning
harness can obstruct the belt.
182
Figure B5 Seat belt geometry in a typical M2 vehicle with a flexible
wheelchair space
None of the M1 and M2 vehicles examined in the field study provided a
head and back restraint for the wheelchair user. Furthermore, in the
smaller vehicles, the rear of the dummy’s head was in close proximity to
the vehicle structure or boarding aid. This is illustrated in the image on
the left of Figure B6. The amount of space in front of the wheelchair was
also important, but varied significantly between vehicles. In one of the
smallest vehicles, the space was limited and the legs of the dummy were
adjacent to rigid parts of a folded seat. This is illustrated in the image on
the right of Figure B6. It is possible that the head of a child in a similar
position may also have been able to contact these parts in a collision.
183
Figure B6 Wheelchair space in two typical M1 vehicles
B.3 M1 and M2 rear facing
Three vehicles were examined in which a passenger in a wheelchair
travels rear facing. These were all M1 category vehicles and were either
purpose built or specially adapted to function as a taxi. No M2 vehicles
were found in which a wheelchair user regularly travels rear facing.
Figure B7 shows the passenger compartment in a typical vehicle. The
image on the left shows the bulkhead that separates the driver and
passenger compartments and the image on the right shows the forward
facing vehicle seats at the rear of the passenger compartment.
184
Figure B7 Passenger compartment in a typical purpose built or adapted
taxi
Figure B7 highlights the key features of purpose built or adapted taxis
that are relevant to the carriage of children in wheelchairs. Firstly, there
is the bulkhead that separates the two compartments and is used to
support the back of a wheelchair. In all three vehicles, the surface of the
bulkhead was uneven with a range of materials used for the various
fittings. In addition, there were several interior projections within the
passenger compartment. A two point wheelchair tie-down was
incorporated into the bulkhead to hold the wheelchair in position during
normal driving and in the event of a collision. The vehicle shown in
Figure B7 also included the option of fitting two further attachments to
the front of the wheelchair. All vehicles provided a three point seat belt
for the wheelchair user, which included an upper anchorage on the B
pillar.
The tie-down system in purpose built or adapted taxis usually attaches
to the rear of the wheelchair. However, one of the vehicles examined in
the field study included a new system that attaches to the front of the
wheelchair. This is shown in Figure B8. Although it was not part of the
field study to evaluate this system, it seemed likely that it would not be
as effective as a traditional system that attaches to the rear of the
wheelchair.
185
Figure B8 Wheelchair tie-down system in one purpose built taxi
None of the purpose built or adapted taxis examined during the field
study provided a head and back restraint for rear facing passengers.
Figure B9 shows some examples of the surfaces and structures in the
vehicles that were adjacent to the heads of the dummies when they
were seated in wheelchairs. The distance between the head and these
surfaces varied significantly depending on the wheelchair type and
particular vehicle. In one vehicle, an 80 mm thick foam head support
was attached to the clear centre division, but it was unlikely to afford any
protection in a collision. In the event of a collision, a child’s head would
strike one of these surfaces, which could result in serious head and neck
injuries. It also seems likely that the neck would bend significantly,
possibly leading to extension injury to the cervical spine.
Figure B9 Proximity of head to vehicle structures in purpose built or
adapted taxis
Contact between the rear of the wheelchair backrest and the bulkhead
was prevented by either the push handles or the rear wheels of the
wheelchairs. The size of the gap between the backrest and the
bulkhead depended on the vehicle and the type of wheelchair. An
186
example is shown in Figure B10 with the electric wheelchair. It seems
likely that the wheelchair backrest would fail in these circumstances
because it would not be supported by the vehicle. Alternatively, the
wheelchair would rotate about the rear wheels. In either event, the child
could contact the bulkhead with considerable force, which would
potentially result in multiple injuries.
Figure B10 Example of the gap between the bulkhead and the backrest
that can result in purpose built or adapted taxis
When a wheelchair user is travelling rear facing, the main function of the
seat belt is to minimise contact with any vehicle structures and to help to
distribute the forces across the stronger parts of their body. In a front
impact, the belt may help to reduce the amount that the occupant would
ride up the wheelchair backrest and would minimise excursion towards
the rear of the vehicle as they came back into their wheelchair. All of the
purpose built or adapted taxis in the field study provided a three point
seat belt. The anchorages of the lap part of the belt were located at the
bottom of the bulkhead and were relatively wide, probably to
accommodate larger wheelchairs. The anchorage of the diagonal part of
the seat belt was located on the B pillar above the shoulder level.
The field study revealed that the path of the seat belt in a purpose built
or an adapted taxi can be influenced by the wheelchair. Figure B11
shows a six year old dummy seated in a manual wheelchair. The image
on the left shows the lap part of the seat belt positioned over the top of
the armrests. The image on the right shows the lap part of the belt
threaded through a small gap in the armrests and side guards. Clearly,
the geometry of the lap part of the seat belt is much better in the image
187
on the right of the figure. However, this set up was difficult to achieve
and involved a lot of contact with the dummy around the hips. This
would be time consuming for the taxi driver and a child and their parent
are unlikely to welcome such contact when the driver fits the restraint.
The diagonal part of the seat belt is also better in the image on the right,
but the ideal route cannot be achieved because the upper anchorage
cannot be adjusted. It must be pointed out, once again, that
manufacturers of wheelchairs intended for use on a vehicle usually state
that the wheelchairs should be used only forward facing. There is,
therefore, a discrepancy between the recommended use outlined by
wheelchair manufacturers and the situation in some vehicles.
Figure B11 Seat belt geometry with a manual wheelchair in an adapted
taxi
Although the effects of poor seat belt geometry may be less important
for rear facing children compared with forward facing children, it might
lead to greater vertical excursion and less favourable belt paths. A child
would therefore be at risk of head and neck injury due to head contact
and a greater risk of soft tissue injuries from the seat belt.
B.4 M3 forward facing
Two M3 vehicles were included in which a passenger in a wheelchair
would travel forward facing. These were coaches. Although they were
not certified as compliant with the Public Service Vehicles Accessibility
188
Regulations 2000 (SI 2000 No.1970; as amended), they included a
wheelchair space that was consistent with the requirements of the
Regulations. Figure B12 shows the wheelchair space in one of the
vehicles. Aftermarket wheelchair tie-down and occupant restraint
systems were included in the vehicle, to be fitted by the driver. There
was no upper anchorage point for the diagonal part of the seat belt,
hence it would need to be positioned over the shoulder and anchored to
the floor of the vehicle. The benefit of an upper anchorage point
compared with a diagonal belt attached directly to the floor was
established for adults by Le Claire et al. (2003).
Figure B12 Wheelchair space in the coach
The wheelchair space and the arrangement of the wheelchair tie-down
and occupant restraint system in the coaches was very similar to that
observed in minibuses. As a result, the main findings of the study were
also very similar. For instance, the anchorages of the lap part of the belt
and consequently the seat belt buckle were attached to floor tracking
behind the wheelchair. This meant that, once again, the diagonal part of
the seat belt passed high around the ribs before joining the lap belt at
the buckles. This is illustrated with the manual wheelchair in Figure B13.
While this was an important observation about the fit of the seat belt for
children, it was also recognised that this was influenced by the design of
the seat belt. Another seat belt design, such as one that attached
directly to the wheelchair, or to the wheelchair tie-down, would have led
to a different fit.
189
Figure B13 Seat belt geometry with a manual wheelchair in a coach
Figure B13 also highlights that the coaches did not provide a head and
back restraint for the wheelchair. Although there is no requirement to fit
a head and back restraint, some coaches on some scheduled interurban
services are equipped with them. The vehicles examined in the field
study therefore represent the worst case. In a collision, a child’s neck
would extend rearwards following the main impact phase when they
move back into their wheelchair seat. This would increase the risk of
head contact behind the seating position and could lead to soft tissue
neck injuries.
B.5 M3 rear facing
The field study included two vehicles in which a passenger in a
wheelchair travels rear facing. Both vehicles were typical examples of
the low floor buses that are used on scheduled services in urban areas.
A dedicated wheelchair space was provided in each bus and they both
included a padded backrest to support the wheelchair. One bus was
equipped with a vertical stanchion to keep the wheelchair within the
space during normal driving manoeuvres. The other bus was equipped
with a retractable horizontal rail in place of the vertical stanchion.
The wheelchair space in each bus is shown in Figure B14. The images
in the top row of the figure show the bus that was fitted with a vertical
stanchion. The images in the bottom row show the bus that was fitted
with a retractable rail.
190
Bus fitted with a cranked vertical stanchion
Bus fitted with a retractable rail
Figure B14 Wheelchair space in low floor buses
The study highlighted some potential issues of compatibility between
children’s wheelchairs and the padded backrest in low floor buses. This
is illustrated in Figure B15. The image on the left of the figure shows
that the backrest was wider than the distance between the handles on
the manual wheelchair used in the study. This meant that the handles
were unable to pass either side of the backrest. Instead, they rested
against the padded surface, resulting in a gap between the backrest and
the dummy. The head of a child travelling in this way would extend
rearwards in the event of a heavy braking or a collision. This motion
might result in a soft tissue neck injury.
The image on the right of the figure shows that the base of the electric
wheelchair pressed against the mounting structure below the padded
surface of the backrest. Once again, this introduced a gap between the
backrest and the dummy, and hence a child travelling in this way might
191
be at risk of soft tissue neck injury in the event of heavy braking or a
collision.
Figure B15 Wheelchair and backrest interaction in low floor buses
B.6 Conclusions
•
The path of the lap part of the seat belt around the dummy was
influenced by the location of the belt anchorages in the vehicle.
•
The contact area between the dummy pelvis and the belt was
reduced when the lap belt anchorages were positioned on either
side of the wheelchair, compared with anchorages behind the
wheelchair.
•
The diagonal part of the seat belt passed high across the ribs of the
dummy when the lap belt anchorages were positioned behind the
wheelchair.
•
The path of the seat belt was influenced by its design and
arrangement. In the case of aftermarket occupant restraints, it was
recognised that there were a number of different designs that were
available that would result in different belt paths.
192
•
The path of the seat belt was influenced by the design of the
wheelchairs. In certain circumstances, the wheelchairs obstructed
the ideal path of the belt.
•
Some of the vehicle types did not include an upper anchorage for
the diagonal part of the seat belt. It would appear that few of these
vehicles currently include such an anchorage.
•
Some of the vehicle types did not include a head and back restraint
for the wheelchair user. It would appear that few of these vehicles
currently include a head and back restraint.
B.7 Recommendations
•
Manufacturers of wheelchairs, vehicles and restraint systems
should be encouraged to work together to improve the path of the
seat belt for children who travel while seated in their wheelchair.
•
The test programme should examine three main areas of concern
for forward facing wheelchairs: the geometry of the restraint system,
the protection of the child’s head behind the wheelchair and the
amount of clear space around the child.
•
The test programme should examine three main areas of concern
for rear facing wheelchairs: the protection that a child’s head and
neck would receive in a collision, the protection that a child’s torso
would receive during a secondary collision with the bulkhead and
the geometry of the restraint system.
B.8 References
Le Claire M, Visvikis C, Oakley C, Savill T, Edwards M and
Cakebread R (2003). The safety of wheelchair occupants in road
passenger vehicles. Wokingham: TRL.
193
Appendix C. Injury criteria and associated performance
limits
C.1 Hybrid III three year old dummy
Injury assessment criteria
Value
15-ms HIC
36-ms HIC
Head acceleration – peak (g)
Source
570
Eppinger et al., 2000
568
Mertz et al., 2003
1,000
FMVSS 213
1,000
Kleinberger et al., 1998
175
Mertz et al., 2003
Head acceleration – 3 ms (g)
No limit found
Neck flexion moment (Nm)
42
Mertz et al., 2003
Neck extension moment (Nm)
21
Mertz et al., 2003
1,430
Eppinger et al., 2000
1,430
Mertz et al., 2003
1,380
Eppinger et al., 2000
1,380
Mertz et al., 2003
1,070
Mertz et al., 2003
34
Eppinger et al., 2000
28
Mertz et al., 2003
Chest compression rate (m/s)
8.5
Mertz et al., 2003
Chest acceleration – 3 ms (g)
55
Eppinger et al., 2000
Neck axial tension (N)
Neck axial compression (N)
Neck fore/aft shear (N)
Chest compression (mm)
194
C.2 Hybrid III six year old dummy
Injury assessment criteria
Value
15-ms HIC
36-ms HIC
Head acceleration – peak (g)
Source
700
Eppinger et al., 2000
723
Mertz et al., 2003
1,000
FMVSS 213
1,000
Kleinberger et al., 1998
189
Mertz et al., 2003
Head acceleration – 3 ms (g)
No limit found
Neck flexion moment (Nm)
60
Mertz et al., 2003
Neck extension moment (Nm)
30
Mertz et al., 2003
1,890
Eppinger et al., 2000
1,890
Mertz et al., 2003
1,820
Eppinger et al., 2000
1,820
Mertz et al., 2003
1,410
Mertz et al., 2003
40
Eppinger et al., 2000
31
Mertz et al., 2003
Neck axial tension (N)
Neck axial compression (N)
Neck fore/aft shear (N)
Chest compression (mm)
Chest compression rate (m/s)
No limit found
Chest acceleration – 3 ms (g)
60
195
Eppinger et al., 2000
C.3 Hybrid III ten year old dummy
Injury assessment criteria
Value
Source
15-ms HIC
741
Mertz et al., 2003
36-ms HIC
1,000
NHTSA, 2005
190
Mertz et al., 2003
Head acceleration – peak (g)
Head acceleration – 3 ms (g)
No limit found
Neck flexion moment (Nm)
78
Mertz et al., 2003
Neck extension moment (Nm)
40
Mertz et al., 2003
Neck axial tension (N)
2,290
Mertz et al., 2003
Neck axial compression (N)
2,200
Mertz et al., 2003
Neck fore/aft shear (N)
1,710
Mertz et al., 2003
44
NHTSA, 2005
36
Mertz et al., 2003
Chest compression rate (m/s)
8.4
Mertz et al., 2003
Chest acceleration – 3 ms (g)
60
NHTSA, 2005
Chest compression (mm)
C.4 References
Eppinger R, Sun E, Kuppa S and Saul R (2000). Supplement:
development of improved injury criteria for the assessment of advanced
automotive restraint systems II. Washington DC: National Highway
Traffic Safety Administration, US Department of Transportation.
Kleinberger M, Sun E, Eppinger R, Kuppa S and Saul R (1998).
Development of improved injury criteria for the assessment of advanced
automotive restraint systems. Washington DC: National Highway Traffic
Safety Administration, US Department of Transportation.
Mertz H J, Irwin A L and Prasad P (2003). Biomechanical and scaling
bases for frontal and side impact injury assessment reference values.
Proceedings of the 47th Stapp Car Crash Conference. Warrendale, PA:
Society of Automotive Engineers, pp. 155-188.
NHTSA (2005). Federal motor vehicle safety standards: child restraint
systems. Notice of proposed rulemaking. Docket No. NHTSA-200521245. Washington DC: National Highway Traffic Safety Administration,
US Department of Transportation.
196
Appendix D. Test results
The following pages summarise the key test results for each of the two
impact conditions examined in the test programme. Each test is defined
further in the relevant section of the main body of the report.
197
198
6 year
old
3 year
old
Dummy
0.02
83
0.13
0.11
0.07
0.09
0.05
72
93
79
103
73
0.07
70
0.66
0.02
0.10
48
73
87
0.07
0.04
113
68
*
84
0.07
0.09
71
59
0.03
kN
g
62
Fore
0.80
1.03
0.68
0.90
0.83
0.36
0.82
1.32
0.77
1.32
1.64
1.29
2.33
0.80
1.21
0.93
kN
Aft
Upper neck
shear force
Head
res.
3 ms
2.57
4.40
3.31
4.80
2.57
1.34
3.04
2.13
1.28
2.31
2.40
2.17
4.22
2.20
1.62
1.20
kN
Tens.
0.08
0.03
0.09
0.02
0.04
0.26
0.42
0.07
0.02
0.03
0.05
0.03
0.06
*
0.36
0.07
kN
Comp.
Upper neck
axial force
8
22
19
17
37
9
16
20
30
7
17
19
12
26
19
25
Nm
Flex.
30
42
26
40
27
10
54
20
20
22
31
21
33
31
25
21
Nm
Ext.
Upper neck
moment
*The neck load cell developed a fault during this test; however, the fault occurred after the main loading phase.
M1 vehicle seat and child
restraint
M2 vehicle seat and child
restraint
M2 vehicle seat
Buggy –
Reclined
supportive
Upright
Manual –
Upright
basic
(M1)
Upright
Tilted
Supportive
Tilted
seating unit
(guide)
Tilted (5 pt)
M2 vehicle seat
Buggy –
Reclined
basic
Buggy –
Upright
supportive
Electric
Upright
Manual –
Reclined
basic
Reclined
Wheelchair
Backrest
angle
D.1 M1 and M2 forward facing test results
76
47
39
56
43
30
54
42
42
41
54
43
53
48
56
48
Res.
3 ms
g
29
36
23
36
17
8
39
22
39
27
31
26
35
27
32
34
mm
Comp.
Chest
3.35
0.07
1.16
0.67
0.07
1.37
0.12
0.24
0.49
0.07
0.84
0.37
0.16
0.46
0.59
0.27
kN
Lumbar
spine
comp.
g
87
42
40
59
47
41
64
41
41
52
45
53
54
57
60
50
Pelvis
res.
3 ms
4.18
4.65
3.63
5.54
4.60
N/A
5.24
1.78
1.42
2.74
2.10
1.20
2.14
kN
No
record
No
record
2.74
Diag.
belt
force
199
M2 vehicle seat
Buggy –
Upright
basic
Electric
Upright
Manual –
Upright
active
Manual –
Upright
basic
Upright
Supportive
Upright
seating unit
(5pt)
Tilted
Backrest
angle
10 year
old
Dummy
0.01
0.14
75
93
0.32
84
0.04
0.14
84
33
0.11
64
0.09
kN
0.16
g
88
59
Fore
Head
res.
3 ms
1.54
0.51
1.24
1.11
1.19
1.63
0.99
kN
1.19
Aft
Upper neck
shear force
4.90
1.09
2.76
3.47
3.63
4.23
2.85
kN
4.32
Tens.
0.07
0.06
0.06
0.03
0.40
0.12
0.26
kN
0.89
Comp.
Upper neck
axial force
M1 and M2 forward facing test results (continued)
Wheelchair
D.1
32
10
5
43
37
14
29
Nm
36
Flex.
55
26
37
54
52
45
33
Nm
58
Ext.
Upper neck
moment
47
28
47
45
41
44
45
Res.
3 ms
g
50
28
17
37
23
34
27
20
mm
28
Comp.
Chest
0.03
1.14
0.45
0.28
0.50
0.89
0.72
kN
1.07
Lumbar
spine
comp.
g
48
39
35
42
40
35
46
48
Pelvis
res.
3 ms
3.98
N/A
3.11
2.66
2.14
2.73
3.82
kN
4.71
Diag.
belt
force
200
Electric
Manual – active
Manual – basic
Supportive
seating unit
Buggy – basic
Vehicle seat
Manual – basic
Supportive
seating unit
Vehicle seat
Buggy –
supportive
Electric
Vehicle seat
Wheelchair
N/A
Upright
Upright
Tilted
N/A
Upright
Reclined
Upright
N/A
Upright
Reclined
Upright
Upright
Upright
Upright
Tilted
10 year
old
6 year old
3 year old
Backrest
Dummy
angle
Res.
3 ms
g
102
124
141
77
124
99
123
55
127
114
105
83
134
120
69
63
717
3982
2239
585
1152
657
949
350
922
1482
825
399
973
1161
467
265
HIC36
Head
D.2 M1 and M2 rear facing test results
Aft
kN
0.15
0.34
0.31
0.98
0.13
0.65
0.18
1.06
0.32
1.25
0.70
0.18
1.50
1.44
0.34
0.34
Fore
kN
0.32
0.63
1.20
0.12
1.77
0.70
0.28
0.50
1.19
1.02
0.93
0.35
0.97
0.94
0.81
0.17
Upper neck
shear force
kN
0.58
2.54
2.20
0.56
1.99
3.80
1.37
1.71
3.22
7.82
1.83
0.93
2.50
2.10
2.28
1.93
Tens.
kN
0.42
0.53
1.07
0.19
1.44
1.10
0.40
0.40
1.29
0.88
0.60
0.55
0.70
1.10
0.70
0.51
Comp.
Upper neck
axial force
Nm
23
28
77
14
70
109
33
36
140
88
92
28
99
88
64
27
Flex.
3
20
12
46
10
42
10
88
29
76
64
34
86
100
35
12
Nm
Ext.
Upper neck
moment
Res.
3 ms
g
50
51
148
87
59
69
70
46
52
74
70
53
77
68
57
74
Chest
kN
0.31
0.48
1.09
0.67
0.30
0.62
1.08
0.75
3.02
2.88
3.15
3.20
1.78
5.57
1.31
5.24
Lumbar
spine
comp.
65
55
113
117
44
72
88
42
77
67
200
49
64
54
40
100
g
Pelvis
res.
3 ms
The safety of child wheelchair occupants in
road passenger vehicles
TRL Report
TRL667
The study comprised a number of elements leading to a dynamic sled test programme with
instrumented child dummies. The research found that children in wheelchairs do not receive a level
of protection that is comparable to that for children in child restraints or vehicle seats. Changes
in legislation are therefore required to address and hence improve their protection. There are
three key influences: the vehicle, the restraint system and the wheelchair. All three areas must be
addressed for improvements in protection to be made, and for the greatest improvements, vehicle,
restraint system and wheelchair manufacturers must work together.
Related publications
TRL559
Review of the road safety of disabled children and adults. K Williams, T Savill and A Wheeler. 2002
PPR076
Development of measures for improving child protection in minibuses, buses and coaches.
G J L Lawrence and W M S Donaldson. 2006
CT22.4
Transport for the elderly and disabled update (2004-2007)
CT111.2
Taxi and paratransit update (2001-2005)
TRF8
The safety of wheelchair occupants in road passenger vehicles. M Le Claire, C Visvikis, C Oakley, T Savill
and M Edwards. 2003
The safety of child wheelchair occupants in road passenger vehicles
This TRL Report presents the findings of a study carried out by TRL for the UK Department for
Transport (DfT). The aim of the study was to examine the safety of children in wheelchairs in road
passenger vehicles. The key question was whether children who remain seated in their wheelchairs
are afforded a level of protection that is comparable to that for children travelling in a vehicle based
restraint system.
The safety of child wheelchair
occupants in road passenger
vehicles
C Visvikis, M Le Claire, O Goodacre,
A Thompson and J Carroll
Price code: T
ISSN 0968-4107
Published by
IHS
Crowthorne House, Nine Mile Ride
Wokingham, Berkshire RG40 3GA
United Kingdom
Willoughby Road, Bracknell
Berkshire RG12 8FB
United Kingdom
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T:
F:
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W:
+44 (0) 1344 773131
+44 (0) 1344 770356
[email protected]
www.trl.co.uk
TRL667 Cover with spine.indd 1
+44 (0) 1344 328038
+44 (0) 1344 328005
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TRL667
TRL
24/06/2008 11:08:41
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