An assessment of cars for small drivers

An assessment of cars for small drivers
Loughborough University
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An assessment of cars for
small drivers
This item was submitted to Loughborough University's Institutional Repository
by the/an author.
Citation: WELSH, R., CLIFT, L., MORRIS, A., COOK, S. and WATSON, J.,
2003.
An assessment of cars for small drivers.
Loughborough: Loughborough
University
Metadata Record: https://dspace.lboro.ac.uk/2134/515
Please cite the published version.
Assessment of cars
for small drivers
(PPAD 9/33/85)
Prepared for:
Department for Transport
Prepared by
Ruth Welsh, VSRC, ESRI
Laurence Clift, TTEC, ESRI
Andrew Morris, VSRC, ESRI
Sharon Cook, TTEC, ESRI
James Watson, Cranfield Impact Centre
©
September 2003
Assessment of Cars for Small Drivers
Sept 2003
Executive summary
•
Analysis of the CCIS accident data showed that drivers up to 160cm in height
repeatedly have the highest rate of AIS 2+ injury across all body regions and
that a significant relationship exists between height and head injury outcome.
Shorter drivers up to around 160-165 cm in height have an increased risk of
serious head injury above the average risk normalised across the entire
population. In depth case analysis did not find evidence for a relationship
between head injury and proximity to the steering wheel for those drivers with
serious head injury.
•
Data collected in a survey of 27 drivers known to have been involved in an
accident showed leg length to be the best indicator of steering wheel to chest
distance. This was followed by lower arm length and total arm length. Height
alone is not a good indicator of seating proximity. Previous research indicates
that the optimal driving position is dependent upon eye location and reach to
the steering wheel and pedals. This also suggests that sitting eye height and
upper/lower arm/leg lengths would be relevant to determining the seated
position adopted by small drivers.
•
In a sample of 120 drivers, small drivers were found to sit with their chests
closer to the steering wheel than the driving population as a whole, but
typically only about 6 - 8 cm and on average they have a chest to hub distance
of 32 cm. Small drivers are unable to sit further away from the steering wheel
primarily because their leg length dictates the proximity of the SRP (the point
at which the seat back and base join, referred to as the ‘seat reference point’)
to the steering wheel and the seat back angle can only provide limited
compensation. Vision and reach to the pedals are the critical factors in small
driver seating position choice. Small driver vision is compromised for low
speed manoeuvres.
•
Women make up a significantly larger proportion of small drivers than men
because of their reduced stature. However, women also have smaller torso's
than men of the same height, which means that when seated their head is lower
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than a similarly sized male. It is also the case that women have shorter arms
than men, suggesting a need to be closer to controls to achieve the same
degree of comfort and usability. These factors combine to compound to the
positional limitations faced by smaller drivers and to more seriously
compromise women.
•
Small drivers are less aware of the safety consequences of sitting too close to
the steering wheel and some believe sitting closer to the steering wheel is
better for airbag performance. They are less knowledgeable about steering
wheel adjustment and find it harder to operate than the normal population
•
Seating posture is learned and strongly maintained in established and new
vehicles with a high degree of precision hence gaining changes in posture are
unlikely through education and information. An alternative seating position
further from the steering wheel is unpopular. Seat position is considered
important for small drivers, and provides a significant part of the car purchase
procedure
•
A review of remedial measures and counter actions indicated that there were
various means for reducing the risks to drivers posed by airbags. In the
medium to long-term, airbag design is being addressed in order to more
appropriately match the airbag deployment characteristics to the characteristics
of the occupant and type of crash. In the interim, measures that reduce the risk
of injury by increasing the distance between the driver and the airbag can be
employed. The key to the successful use of these measures is to inform
drivers of the risk posed by airbags and the alternative means for reducing it.
•
Finite element modelling has established a recommended steering wheel to
chest distance of 32 cm for small drivers of airbag equipped vehicles with a
minimum of 25 cm. The recommendations presented are based upon 21 mph,
25 mph and 35 mph impacts into a rigid barrier. In the case that the minimum
can not be achieved in a given vehicle remedial actions should be taken, or an
alternative vehicle considered.
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•
Sept 2003
The recommended distances do not present an excessive increase in the risk of
serious head, neck or chest injury and do not result in an adverse scenario for
the 50th percentile male dummy.
•
A draft leaflet has been proposed that gives advice to smaller drivers on the
selection of an appropriate driving position that does not compromise safety.
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Table of contents
1.0
Introduction........................................................................................................1
1.1.
Accident Data.................................................................................................3
1.2.
Human Factors Assessment ...........................................................................3
1.3.
Guidelines for the Small Stature Driver.........................................................3
1.4.
Additional Module .........................................................................................3
2.0
Accident Data.....................................................................................................5
2.1.
Literature review - Smaller drivers and crash-injury risk ..............................5
2.2.
Data analysis objectives.................................................................................7
2.3.
Selection of Data............................................................................................7
2.4.
Data Overview ...............................................................................................9
2.5.
The relationship between height and gender ...............................................16
2.5.1.
Multiple regression ..............................................................................17
2.5.2.
General linear modelling......................................................................19
2.6.
Rate of serious injury by height ...................................................................20
2.6.1.
MAIS....................................................................................................20
2.6.2.
Head Injury (including cranium) .........................................................22
2.6.3.
Chest Injury..........................................................................................23
2.6.4.
Abdominal Injury.................................................................................24
2.6.5.
Lower Extremity Injury .......................................................................26
2.7.
Population at increased risk .........................................................................28
2.8.
Detailed Injury Analysis ..............................................................................30
2.8.1.
CASE 85502/1/1 ..................................................................................32
2.8.2.
CASE W85432/1/1 ..............................................................................33
2.8.3.
CASE W70547/1/1 ..............................................................................34
2.8.4.
CASE H55410/2/1 ...............................................................................35
2.8.5.
CASE L12371/1/1................................................................................36
2.8.6.
CASE B32389/2/1 ...............................................................................37
2.8.7.
CASE B31965/1/1 ...............................................................................38
2.8.8.
CASE B32483/1/1 ...............................................................................39
2.8.9.
CASE 12895/1/1 ..................................................................................40
2.8.10. CASE L13111/1/1................................................................................41
2.8.11. CASE B31922/1/1 ...............................................................................42
2.8.12. CASE B32419/1/1 ...............................................................................43
2.8.13. CASE H55409/2/1 ...............................................................................44
2.8.14. CASE H55825/1/1 ...............................................................................45
2.8.15. CASE W70258/1/1 ..............................................................................46
2.9.
Recommendation for human factors assessment .........................................47
3.0
Assessment of recommended chest to steering wheel distance .......................48
3.1.
Seating preferences and injury outcome for CCIS drivers ..........................48
3.2.
The NHTSA recommendation .....................................................................59
4.0
Human Factors Assessment .............................................................................61
4.1.
Literature Review – Drivers’ positioning within the car .............................61
4.2.
Human factors assessment objectives..........................................................65
4.3.
Anthropometric analysis of adults with small stature..................................66
4.3.1.
Aim ......................................................................................................66
4.3.2.
Anthropometric research data ..............................................................66
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Female..........................................................................................68
4.3.3.
Anthropometric survey ........................................................................69
4.3.4.
Conclusions..........................................................................................70
4.4.
Exploration of the positions adopted by small drivers.................................71
4.4.1.
Aim ......................................................................................................71
4.4.2.
Methodology ........................................................................................72
Sample specification.......................................................................................73
Data collected .................................................................................................74
4.4.3.
Results..................................................................................................74
Participant details ..........................................................................................74
The driving position adopted ........................................................................78
Reasons for adopting that position...............................................................90
Access to primary and secondary controls ..................................................99
Quality of drivers view of the road.............................................................102
Knowledge of adjustment............................................................................104
Perceived adequacy of position...................................................................106
Importance of driving position in car purchase........................................107
Awareness of hazards of close seating position .........................................108
Alternative driving positions.......................................................................113
4.4.4.
Conclusions........................................................................................118
4.5.
Consideration of counter measures and remedial actions..........................119
4.5.1.
Aim ....................................................................................................119
4.5.2.
Methodology ......................................................................................119
4.5.3.
Findings..............................................................................................119
Seat adjustability..........................................................................................119
Pedals ............................................................................................................121
Steering wheel...............................................................................................122
Airbag design................................................................................................124
Driver education...........................................................................................126
4.5.4.
Conclusions........................................................................................127
5.0
Finite Element Modelling ..............................................................................128
5.1.
Model set-up ..............................................................................................128
5.1.1.
Dummy ..............................................................................................128
5.1.2.
Seat.....................................................................................................128
5.1.3.
Airbag properties ...............................................................................129
5.1.4.
Seatbelt Properties .............................................................................129
5.1.5.
Measurement of Chest to Steering Wheel .........................................130
5.1.6.
Pulses .................................................................................................133
5.2.
Simulation matrix.......................................................................................134
5.3.
Results........................................................................................................135
5.3.1.
Proximity to steering wheel ...............................................................135
5.3.2.
Injury outcome ...................................................................................140
Head injury...................................................................................................141
Neck Injury...................................................................................................144
Chest Injury..................................................................................................146
5.4.
Discussion ..................................................................................................147
6.0
Regulatory Impact Assessment (RIA) ...........................................................151
7.0
Conclusions and Recommendations ..............................................................153
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8.0
Future work....................................................................................................161
9.0
References......................................................................................................162
Appendix 1.................................................................................................................166
Appendix 2.................................................................................................................175
Appendix 3:................................................................................................................184
Appendix 4:................................................................................................................187
Appendix 5.................................................................................................................190
Appendix 6.................................................................................................................195
Appendix 7.................................................................................................................201
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1.0
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Introduction
It is a well-established fact that females are smaller in stature on average than males.
Research has also examined injury differences between males and females in crashes,
these are considered in the literature review within section 2.
It is evident that previous research has focussed in the majority upon gender based
analysis. It is accepted that gender and stature are unavoidably highly correlated
variables however a separate stature based analysis is warranted to establish what
differences exist in injury patterns when stature is considered as opposed to gender.
Aspects for improving the crashworthiness of cars for women, and hence in the main
smaller than average stature drivers, are already recognised by the car industry. A 5th
percentile Hybrid III dummy is available for vehicle development and although not
used in regulations or Consumer tests, some manufacturers routinely use the dummy
to support restraint design. However, there then exists an underlying assumption that
the small driver population is adequately catered for by the 5th percentile female. 95%
of women are below the 50th percentile male in height and so it is sensible to use
smaller dummies to assess likely injury experience. But, it is equally true that 95% of
women are taller than the 5th percentile and it may be that the stature of the 5th
percentile female dummy does not best represent those in the population who have
higher injury rates. A full stature based analysis of the accident data will reveal which
part of the population, according to stature, have an increased risk of injury above that
standardised across all statures.
An underlying hypothesis by way of explanation for any perceived increase in injury
to those of shorter stature is the propensity for shorter drivers to sit closer to the
steering wheel than their taller counterparts. In terms of potential contact with
intruding frontal structures and possible adverse interaction with a deploying airbag,
this situation would seem disadvantageous.
Several observational studies have highlighted the differences in seating position
adopted by drivers of varying stature. Research in the UK (Parkin 1993) has shown
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that for the population observed the 5th percentile female sits some 21.5cm closer to
the hub than the 95th percentile male, and the 50th percentile female over 6 cm closer
than the 50th percentile male. The factors that influence a driver’s chosen seating
position are not clearly understood and are examined in some detail in this project.
There have also been a number of studies that have examined the types and
mechanisms of injuries that can be caused by airbags in certain situations. Kirk (2002)
in an extensive review of the benefits of airbags in European vehicles, showed the
probability of AIS 2+ head injury to be greatly reduced in airbag-equipped vehicles
with shorter drivers having the greatest benefit. However, in some circumstances it is
possible to have unfavourable interaction with the airbag during the early deployment
phase resulting in serious injury not least if the driver is in close proximity to the
steering wheel prior to impact.
Current guidelines stipulating an adequate chest to steering wheel distance that will
minimise the risk of serious head injury from the deploying bag are based upon advice
given by the NHTSA. These recommendations were developed for the American fleet
where due to poor seat belt wearing rates, the airbag is seen more as a primary rather
than a supplementary restraint and are designed to protect both the head and the chest
in the event of an impact. As a consequence, the airbags tend to be larger and more
aggressive than those typically found in the European fleet, some early European bags
were modelled more upon those seen in the Sates. It is prudent therefore to examine
the justification behind the current guideline and to establish it’s applicability to the
driving population in the UK.
The work that has been carried out during the course of this project falls into three
main sections; an analysis of the accident data, a human factors assessment, and the
development of guidelines for good driving practice for small stature driver which
draws upon the finding of the two previous sections.
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1.1.
Sept 2003
Accident Data
A literature review is undertaken to identify previous studies relating to small drivers
and injury risk. An analysis of the accident data is made to identify by stature and
gender that part of the driver population seen to be substantially more at risk of injury
than the average. A subsequent detailed injury analysis assesses to what extent
proximity to forward intruding structures and the airbag module are factors in this
observed increased risk of injury. Drivers involved in accidents identified through the
co-operative crash injury study (CCIS) are asked to provide additional
anthropometrical information in order to correlate injury outcome with seating
position. A review of the current guidelines with respect to proximity to the airbag
module is made.
1.2.
Human Factors Assessment
A literature review to identify previous work examining drivers’ seating positions is
undertaken. Additionally, the human factors assessment explores the seating positions
adopted by small drivers. The specific population referred to as ‘small drivers’ will
have been determined based on the crashworthiness assessment of the accident data
analysis. Consideration will be given to counter measures and remedial actions
available to those who find themselves unavoidably close to the steering wheel than
advisable.
1.3.
Guidelines for the Small Stature Driver
The results from the previous two sections are reviewed and a set of guidelines
produced that will enable drivers to evaluate any car in relation to their own specific
needs. It is not the intention to rate individual makes and models of car according to
their suitability for the small driver, but to make the driver aware of both safety and
ergonomic issues that should be considered when purchasing a vehicle.
1.4.
Additional Module
During the course of the project it became clear that an additional modelling module
was required in order to determine the guideline recommending a suitable proximity
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to the airbag module. The rationale for this decision is given in the section reporting
upon the accident data, and a report on the activities undertaken within the additional
module is included as an appendix.
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2.0
Accident Data
2.1.
Literature review - Smaller drivers and crash-injury risk
Research has examined injury differences between males and females in crashes.
Evans (1988 and 1991) was able to show that for an impact of a given severity,
females ages 15 to 60 are more likely to be killed than males. However he did not
elaborate as to the underlying cause, although stature is thought to have been a factor
in addition to biomechanical and physiological differences. Stone (1996) also found
that female drivers were more likely to be injured than male drivers and the reasons
for this included the fact that females were generally shorter in stature than males,
thus necessitating closer positioning to the steering wheel and also because of
‘inherent physical frailty’. He also observed that shorter drives (both males and
females) had an increased risk of lower extremity fractures. This finding was also
reported by Dischinger (1992); she noted that drivers less than average height in the
US (5ft 7ins or 1.70metres) had a 64% increase in lower extremity fracture rates with
most injuries being to the ankle/tarsals. Crandall et al (1996) found that ‘shorter’ front
seat occupants were also at greater risk of lower limb injury with women being at
greater risk than men. They postulated that increased risk of injuries for smaller
drivers was associated with the way that the feet were used to operate the brake pedal.
Using a driver simulator experiment, smaller female drivers were found to lift their
feet from the floor-pan in order to brake whilst taller drivers were found to ‘pivot’ the
foot around the floor-pan. The underlying assumption here is that the position of the
foot/ankle during the crash can have a major effect on injury outcome because of the
biomechanical properties of the lower limb. In such studies of differences in injury
risk between sexes, it should not be overlooked that females may have a tendency to
drive smaller cars (Ginpil and Attwell, 1994).
There have also been a number of studies that have examined the types and
mechanisms of injuries that can be caused by airbags in certain situations. Dalmotas et
al (1996) reported on a study comparing airbag-equipped and non airbag-equipped
vehicles in the US. They found that females (and by implication, shorter stature
drivers) had consistently higher injury and harm rates in the airbag-equipped vehicles
compared to the non airbag-equipped vehicles. They concluded in their report that
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…“as reflected by the injury experience of females in both the Canadian and US
collision data, the segment of the driving population who place their seats ahead of the
mid-seating position cannot be overlooked in regulations governing occupant
protection systems”. In addition, there is now a sizeable body of work, which
demonstrates that injuries are caused by drivers contacting the deploying airbags (Hill
and Mackay, 1997). Several injuries are thought to be caused by contact with
deploying airbag systems. These include facial and upper extremity injuries (such as
bruising, abrasion, peri-orbital injury and ocular injury) caused by ‘bag-slap’ as well
as fractures of the upper extremity and thermal burns. Closer proximity to the steering
wheel when the airbag deploys is thought to correlate with magnified risk of such
injuries.
As a consequence of such findings, it is suggested that female drivers in particular risk
contacting the airbag whilst it is still deploying in the UK and Europe and also in
Australasia (where a significant portion of the fleet comprises imported European
vehicles). This is the case even though the airbag systems (also known as
Supplementary Restraint Systems or SRS) used in European and Australasian
countries are less aggressive than the systems used in North America (which are also
known as Primary Restraint Systems or PRS) where small female drivers have now
been advised to de-activate the driver airbag following a series of deaths arising from
interaction with the explosive force of the airbag, not the impact of the vehicle.
Injuries to such drivers were found to occur to the head, neck and chest. It became
clear that the problem arose because North American airbags were designed to
optimally accommodate 50th percentile male crash dummies (i.e. the ‘average’
person) and this decision placed smaller females at risk in particular, since they have
been found to sit much closer to the steering wheel (Porter and Porter 2001, Parkin et
al, 1993 – figure 29 ). . This issue reinforces the view that ‘average’ or 50th percentile
values should never be used for specifying clearances, minimum reach distances or
maximum control forces.
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2.2.
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Data analysis objectives
The primary objective of the data analysis section of the project has been to identify
by stature those drivers substantially more at risk of injury than the risk seen by the
population as a whole. The questions asked for this part of the work were
•
What if any are the differences in overall injury for small and tall stature
drivers?
•
What if any are the differences in the accidents experienced by short and tall
stature drivers?
•
For which body regions do we see a relationship between injury severity and
height?
•
By body region, who is substantially more at risk of AIS 2+ injury?
•
What if any are the differences in the specific injuries received by those in the
higher risk category compared to those not?
•
Is it possible to establish the cause of the serious injuries?
•
Does a pattern emerge indicating proximity to frontal structures as an issue for
small stature drivers?
2.3.
Selection of Data
The Co-operative Crash Injury Study (CCIS) data covers the full range of crash
modes experienced by passenger cars. The data are sampled on vehicle age, vehicle
damage and injury outcome. To be included in the database, the accident must have
included at least one car that was at most seven years old at the time of the crash, was
towed away from the accident scene and in which an occupant of the car was injured
The data are also collected within a stratified sample which is biased towards ‘fatal’
and ‘serious’ injury outcome crashes (KSI). Of those occurring within the
geographical sampling regions approximately 80% of all the KSI crashes, and around
10-15% of the slight injury outcome crashes are investigated.
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Each crash mode leaves the driver vulnerable to a particular range of injuries
associated with that mode. Previous research has intimated that undue proximity to
the intruding structures and to the airbag module during a frontal collision is
detrimental in terms of injury outcome. This may particularly be the case for smaller
drivers who may adopt a more forward seating position than their taller counterparts.
This study is concerned with assessing vehicles for small drivers. Frontal impacts
have been chosen to look at issues of crashworthiness as this is believed to be a crash
mode where a difference in the injury pattern between smaller and taller drivers will
be seen and where driver seating preference has a relationship with injury outcome.
The age of the vehicle is an important consideration within the analysis as structural
design changes constantly to meet with changing legislative safety requirements.
However any selection of the data results in fewer cases for analysis. Cases included
for this project come from phases 4, 5 and 6 of the CCIS, that is crashes occurring
from 1992 to the present. It was hoped that the vehicle age could be restricted to those
manufactured post 1990, an important milestone in frontal impact legislation,
however this substantially reduced the number of cases. As a result, vehicles
manufactured post 1985 are included in the analysis.
As the analysis is concerned with identifying sections of the population according to
their height, only those cases where the driver’s height was known have been
included.
In summary, the data used for the overview analysis comprises 1472 drivers such that
•
Accident occurred 1992 – present
•
Driver was restrained
•
Crash mode was a single frontal impact
•
Driver height is known
•
Vehicle manufactured post 1985
In some of the subsequent analysis, further selection of cases has taken place. This is
discussed at the appropriate points.
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2.4.
Sept 2003
Data Overview
This activity was designed to take a preliminary look through the data for any obvious
differences in the type of frontal accident experienced by short and tall drivers which
may have a bearing on any increased risk of injury observed later. It also takes a broad
look at any differences in injury outcome between short and tall drivers.
For this section, the data has been broadly categorised by stature defined as
•
Short <170 cm (N=468)
•
Tall > 174 cm (N=617)
This categorisation gives clear distinction between the two groups whilst maintaining
a reasonable balance of cases between the groups.
Figure 1 shows how height is distributed within the sample.
Figure 1 Distribution of driver height
tall
short
50%
percentage of occupants
45%
40%
35%
30%
25%
20%
15%
10%
5%
0%
5+
19
4
19
019
9
18
518
4
18
018
9
17
517
4
17
017
9
16
516
4
16
016
9
15
515
4
15
015
9
14
0-
height range (cm)
The two groups are completely distinct, but together follow a normal distribution. As
would be expected, the number of cases falling in to the categories at the extremes of
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the distributions is low. This is purely a product of the natural height variation with
the adult population.
The nature of the frontal impact can be categorised according to the principle
direction of force of the impact, the crash severity and the collision partner. These
variables have been explored to look for any obvious differences in the type of impact
experienced by the two groups according to stature.
Figure 2 shows the direction of force of the impact. This works around the idea of a
clock face, where a 12 o’clock impact would be directly into the front of the vehicle, a
3 o’clock impact perpendicular to the right side of the vehicle and a 6 o’clock would
be directly into the rear.
Figure 2 Principle direction of force of impact (PDOF)
tall
short
80%
percentage of occupants
70%
60%
50%
40%
30%
20%
10%
0%
10
11
12
1
2
clockface direction of impact force
As can be seen from the chart, there is little difference in the distribution of the PDOF
for the tall and short categories of drivers. The frontal impacts are predominantly
directly into the front of the vehicle, oblique frontal impacts accounting for around a
quarter of impacts in both cases.
Figure 3 shows the crash severity measured in km/hr and as calculated by the Crash3
collision damage computer programme. The measure presented is Delta V which
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gives a measure of the instantaneous change of velocity experienced by the vehicle at
the time of the impact.
Figure 3 Delta V
tall
short
35%
percentage of occupants
30%
25%
20%
15%
10%
5%
0%
0-9
10-19
20-29
30-39
40-49
50-59
60-69
70-79
80+
delta-V (km/h)
There are small variations in the Delta V between the short and tall driver categories.
For the shorter drivers the Delta V is distributed more in the higher crash severities
than for the tall drivers, however on balance across all severities the differences are
not great. The slightly higher Delta V experienced by the short category could be a
product of the difference in the size of vehicle driven by the two groups which is
illustrated in figure 6.
Figure 4 illustrates the collision partner for each of the vehicles included in the
analysis. The type of collision partner can influence injury outcome due to the
different levels of intrusion experienced for different objects struck.
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Figure 4 Collision partner
tall
short
80%
percentage of occupants
70%
60%
50%
40%
30%
20%
10%
0%
car
van
truck
fixed
other/unknown
collision partner
It is clear that there is no difference in the collision partner for the two groups in the
sample. Impacts are predominantly car to car. The fixed object category includes pole
type impacts such as trees and signposts.
Thus, in terms of the type of impact it is reasonable to assume little or no differences
in the collisions experienced by the tall and the short groups of drivers.
Other factors that may influence injury outcome in terms of vehicle crashworthiness
and which can be analysed using the data are vehicle age and size. Previous work
looking at issues for female drivers (Lenard 2001) showed that they tend to drive
smaller but not necessarily older cars than men. We would expect to see a similar
result when the data are split by stature due to the inevitable female bias in the short
height category.
Figure 5 shows the vehicle age distribution for the tall and short driver categories. It
can be seen that the distribution is similar for the two groups. It is certainly not the
case that the short drivers are more often in vehicles with inherently poorer
crashworthiness design.
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Figure 5 Distribution of vehicle age within stature
tall
short
18%
percentage of occupants
16%
14%
12%
10%
8%
6%
4%
2%
0%
0
1
2
3
4
5
6
7
8
9
10+
Age of vehicle (years)
Vehicle size as dictated by the mass of the vehicle is shown in figure 6.
Figure 6 Distribution of vehicle mass within stature
percentage of occupants
tall
short
24%
22%
20%
18%
16%
14%
12%
10%
8%
6%
4%
2%
0%
+
00
15
9
49
-1
00
14
9
39
-1
00
13
9
29
-1
00
12
9
19
-1
00
11
9
09
-1
00
10
9
99
090
9
89
080
9
79
070
9
69
0-
Vehicle mass
There is a visible difference in the distribution of vehicle size with respect to stature
and this reflected in the body type of the vehicle (figure 7). The drivers categorised as
short have a lighter vehicle mass distribution than the tall drivers. Hatchbacks account
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Sept 2003
for the majority of vehicles for both groups, but the proportion is higher for short
drivers (77%) than for tall drivers (66%). It is intrinsically disadvantageous to be in
the smaller of two colliding vehicles and similarly to be in smaller vehicle in the event
of a collision with a road side object.
Figure 7 Distribution of vehicle body type within stature
tall
short
90%
percentage of occupants
80%
70%
60%
50%
40%
30%
20%
10%
0%
sedan
hatchback
estate
other
vehicle body type
We now look for general differences in injury outcome when the accident sample is
broadly categorised by stature into those classified as tall and those short. Injuries
suffered by drivers within the sample are classified according to the Abbreviated
Injury Scale. This is an anatomically based system that classified individual injuries
by body region on a six point ordinal severity scale ranging from AIS 1 (minor) to
AIS 6 (currently untreatable). Consideration is given here to MAIS being the highest
single AIS code across all body regions in a patient with one or more injuries and to
the incidence of injury across the body regions. For those drivers with a MAIS of 2 or
greater we then look at where the AIS 2+ injuries occur.
Figure 8 shows the distribution of MAIS for the two height categories.
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Figure 8 Distribution of MAIS within stature
tall
short
80%
percentage of occupants
70%
60%
50%
40%
30%
20%
10%
0%
1
2
3
4
5
6
MAIS
Figure 8 shows there to be minor observed differences in MAIS for the two
categories. The majority of drivers receive only minor injuries. There are a higher
proportion of short drivers injured to a MAIS level of 3 and over than tall drivers,
though this amounts to only around 3%.
Figure 9 Incidence of injury by body region and stature
tall
short
50%
percentage of occupants
45%
40%
35%
30%
25%
20%
15%
10%
5%
pl
as
h
hi
w
ch
es
t(
sk
el
)
ch
es
t(
in
t)
ab
do
/p
el
vi
s
le
g
(s
ke
l)
ar
m
(s
ke
l)
br
ie
fL
O
C
sp
in
e
(in
he
ad
he
ad
(s
ke
l
)
t)
0%
body region
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Figure 9 shows the incidence of injury of all severities by body region. There is an
observed difference in the incidence of injury between the two groups with the short
drivers exhibiting an increased incidence of injury in all cases except for skeletal arm
injuries.
For those drivers classed as MAIS 2+, figure 10 shows that there are differences in the
distribution of the location of the AIS 2+ injuries between the two groups.
.
Figure 10 Location of maximal injury for MAIS 2+ drivers
tall (N=151)
short (N=133)
50%
45%
percentage of occupants
40%
35%
30%
25%
20%
15%
10%
5%
0%
head
spine
chest
abdo/pelvis
legs
arms
nfs
body region
Shorter drivers exhibit a higher proportion of maximal injuries to the head, spine, legs
and arms than taller drivers, and proportionally fewer to the chest and abdomen.
2.5.
The relationship between height and gender
The previous activity has shown that there are differences in the injuries received by
taller and shorter drivers. Height however is a characteristic strongly related to
gender. It is intrinsic that there is a female bias in the shorter driver category and a
male bias in the taller driver category. Two techniques have been used to try and
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identify the relative contribution of height and gender to the injury outcome; Multiple
Regression and General Linear Modelling.
2.5.1.
Multiple regression
Multiple regression techniques have been used to determine the relative importance of
the different driver characteristics in the prediction of injury outcome to each body
region. It was not the intention to build a predictive model as injury outcome is too
dependent on a number of vehicle based variables particularly crash severity, but by
performing a regression using occupant based characteristics alone the power of each
characteristic can be assessed.
It is important to note that the data used for each body region regression is exactly the
same, so that the distribution of crash severity experienced by the drivers is identical
in each case. This implies that any differences noted in the importance of the driver
characteristics most indicative of injury outcome are not influenced by some
difference in crash severity.
A multiple linear regression was performed for each of the ordinal dependent
variables
•
MAIS
•
Head Severity
•
Cranium Severity
•
Neck Severity
•
Chest Severity
•
Abdomen Severity
•
Leg Severity
Arm severity was not included as it is extremely difficult, given the nature of
occupant dynamics during the crash phase, to determine injury causation for arm
injuries.
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The independent (predictive) variables entered for each regression were
•
Age
•
Gender
•
Height
•
Weight
•
Body Mass Index
The regression determines which of the independent variables are significant in
predicting the outcome of the dependent variable.
The regression results are summarised in table 1
Table 1 Regression on injury outcome and driver characteristics
1st Significant
2nd Significant
Predictor
Predictor
MAIS
MAIS
GENDER
Head Severity
HEIGHT
-
Cranium Severity
HEIGHT
-
Neck Severity
AGE
HEIGHT
Chest Severity
AGE
GENDER
Abdomen Severity
GENDER
BMI
Leg Severity
GENDER
-
Dependent Variable
From the table it can be seen that a relationship between height and gender is most
likely to be found for head, cranium and neck injury.
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2.5.2.
Sept 2003
General linear modelling
The results of the multiple regressions identify those regions where differences in
injury outcome according to height may be significant. In order to determine any
differential effect of height between men and woman general linear modelling was
used including the independent variables gender and height so that the significance of
the interaction between height and gender could be evaluated. The results presented
are for those body regions whereby statistically significant relationships were found
using this modelling technique, specifically the head and lower extremity. Table 2
shows the results from this analysis. A statistically significant interaction term was
found only in the case of lower extremity. No statistically significant interaction term
was observed for head injury. The numbers in the table are the associated ‘p’ values
for each term in the model.
Table 2 Interaction Term for Head and Lower Extremity Severity
Dependent variable
Head severity
Lower ex severity
Independent variable significance
Height
Gender
Interaction term
0.00
0.56
0.52
0.11
0.60
0.04
This analysis indicates that a relationship exists between height and head severity
(inclusive of the cranium). In the case of lower extremity severity there is a
relationship but it is more a product of some interaction between height and gender,
and not distinguishable by either height or gender alone.
These modelling results indicate that in the subsequent analysis there is likely to be
the strongest relationship between injury outcome and height for head injury
(inclusive of cranium injury). It is unlikely that there will be a strong relationship
between injury outcome and height for the other body regions but the analysis in the
next activity has been performed for completeness on those regions where there is
sufficient occurrence of injury for sensible results, those being the head, chest,
abdomen and leg.
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2.6.
Sept 2003
Rate of serious injury by height
In this section the drivers are separated into 10cm height bands and the relationship
between height and injury outcome for the different body regions is considered firstly
with no gender distinction and then when the data are further separated according to
gender. This gives a preliminary indication of those parts of the population seen to be
more at risk of injury. The analysis here focuses on the rate of serious injury outcome.
Serious injury is defined as being at the AIS 2 level or more severe. Despite this
relatively large banding of the data, there remains small numbers of cases in the
smallest and tallest categories. This is simply the product of an analysis that wishes to
examine the extremes of a population. Care is needed when interpreting the results for
small numbers of cases.
2.6.1.
MAIS
Figure 11 gives the rate of MAIS 2+ by height.
Figure 11 Rate of MAIS 2+ within height
45
40
% of drivers within height
35
30
25
20
15
10
5
0
up to 1.5 (14)
1.51-1.60 (180)
1.61-1.70 (437)
1.71-1.80 (558)
1.81-1.90 (249)
> 1.90 (31)
Height (m)
The smallest drivers are injured to a MAIS 2+ level proportionally more frequently
than taller drivers. There are 14 drivers included in the shortest height category of
which over 40% were injured to a MAIS 2+ severity. It should be noted that when
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there are a small number of cases in the sample, single events can dramatically alter
the interpretation. There is an observational trend indicating that the proportion of
drivers with MAIS 2+ injury decreases with height.
The data are now further separated according to gender (figure 12). In this instance
the two upper and two lower height classifications have been combined in order that
both genders be represented within each band. Even so, there remain only 2 female
drivers in the tallest category.
Figure 12 Rate of MAIS 2+ within height and gender
Male
Female
35
N=178
N=129
% of drivers within height and gender
30
N=455
N=308
N=102
25
20
N=278
N=16
15
10
5
N=2
0
up to 1.60
1.61-1.70
1.71-1.80
>1.80
Height (m)
The category with proportionally most MAIS 2+ drivers is small females up to 160
cm in height. This equates to the female 39th percentile. This is followed by men
between 161 and 780 cm. If the smallest male category is discounted where the
sample size is small, the proportion of seriously injured drivers decreases with height
for both sexes.
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2.6.2.
Sept 2003
Head Injury (including cranium)
Figure 13 shows the rate of AIS 2+ head injury within height
Figure 13 Rate of AIS 2+ head injury within height
35
% of drivers within height
30
25
20
15
10
5
0
up to 1.5 (13)
1.51-1.60 (167)
1.61-1.70 (404)
1.71-1.80 (507)
1.81-1.90 (231)
> 1.90 (29)
Height (m)
The shortest drivers exhibit the highest proportion of AIS 2+ head injury. Generally
speaking the proportion with AIS 2+ head injury decreases with height though there is
a slight increase in the tallest drivers, those over and above 180 cm in height.
Figure 14 illustrates the rate of AIS 2+ head injury when the data are split by gender.
Again the two lowest and two highest bands have been combined. The general trend is
for the occurrence of AIS 2+ head injury to decrease with height. This is certainly the
case for women. There is however an increase in the proportion of men with AIS 2+
head injury in the tallest category. Overall, the group with the greatest proportion of
AIS 2+ head injury is the smallest female category, up to 160 cm ( 39%ile female
height). Other than for the shortest group, men have a higher proportion of AIS 2+
head injury than women.
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Figure 14 Rate of AIS 2+ head injury within height and gender
Male
18.0
Female
N=164
% drivers within height and gender
16.0
14.0
N=16
12.0
N=110
10.0
N=258
8.0
N=294
N=409 N=97
6.0
4.0
2.0
N=2
0.0
up to 1.60
1.61-1.70
1.71-1.80
>1.80
height (m)
2.6.3.
Chest Injury
Figure 15 Rate of AIS 2+ chest injury within height
18
16
% of drivers within height
14
12
10
8
6
4
2
0
up to 1.5 (13)
1.51-1.60 (166)
1.61-1.70 (406)
1.71-1.80 (513)
1.81-1.90 (231)
> 1.90 (29)
Height (m)
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There is no clear relationship between height and the proportion of drivers with AIS
2+ chest injury (Figure 15). Observationally, the highest proportion of AIS 2+ chest
injury occurs in the shortest height category, and the lowest proportion in the tallest
height category.
Figure 16 shows the rate of AIS 2+ chest injury when the data are further separated
according to gender.
Figure 16 Rate of AIS 2+ chest injury within height and gender
Male
Female
18
N=112
% drivers within height and gender
16
N=416
N=164
14
N=96
N=294
12
N=258
10
8
N=15
6
4
2
N=2
0
up to 1.60
1.61-1.70
1.71-1.80
>1.80
Height (m)
When the drivers are also segregated by gender, the category with the highest
proportion of AIS 2+ chest injury is men between 161 and 170 cm (3 %ile – 27 %ile),
followed by men between 171 and 180 cm (28%ile – 78 %ile) then the smallest
women up to 160 cm (39%ile). There is no clear linear relationship between height
and rate of AIS 2+ chest injury.
2.6.4.
Abdominal Injury
The shortest drivers have proportionally more AIS 2+ abdominal injuries than any
other category. There is no clear relationship between occurrence of AIS 2+
abdominal injury and height. This can be seen in figure 17.
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Figure 17 Rate of AIS 2+ abdominal injury within height
% with AIS 2+ abdominal injury within height
9
8
7
6
5
4
3
2
1
0
up to 1.5 (13)
1.51-1.60 (166)
1.61-1.70 (406)
1.71-1.80 (513)
1.81-1.90 (231)
> 1.90 (29)
Height (m)
Figure 18 shows the rate of AIS 2+ abdominal injury when the data is separated
further by gender.
Figure 18 Rate of AIS 2+ abdominal injury within height and gender
% with AIS 2+ abdominal injury by sex within height
Male
4
Female
N=164
3.5
N=416 N=96
3
N=258
2.5
N=112 N=294
2
1.5
1
0.5
N=15
N=2
0
up to 1.60
1.61-1.70
1.71-1.80
>1.80
Height (m)
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The category receiving proportionally most AIS 2+ abdominal injuries is small
females up to 160 cm (39 %ile). This is followed by equal proportions for both men
and women between 171 and 180 cm.
2.6.5.
Lower Extremity Injury
The lower extremity body region includes injuries to the pelvis. Figure 19 shows the
rate of AIS 2+ injury to the lower extremity.
Figure 19 Rate of AIS 2+ lower extremity injury
45
% with AIS 2+ leg injury within height
40
35
30
25
20
15
10
5
0
up to 1.5 (13)
1.51-1.60 (166) 1.61-1.70 (406) 1.71-1.80 (513) 1.81-1.90 (231)
> 1.90 (29)
Height (m)
Once again, the shortest drivers have proportionally more AIS 2+ leg injuries than any
other category. There is no clear relationship between occurrence of AIS 2+ leg injury
and height.
Figure 20 presents the rate of AIS 2+ lower extremity when gender is also taken into
consideration.
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Figure 20 Rate of AIS 2+ lower extremity injury within height and gender
Male
Female
20
N=164
% of drivers within height and gender
18
16
N=416
14
N=112
12
N=96
10
N=294
N=258
8
6
4
2
N=15
N=2
0
up to 1.60
1.61-1.70
1.71-1.80
>1.80
Height (m)
Again, the most vulnerable category in terms of rate of AIS 2+ injury are the smallest
women, those up to 160 cm in height.
To summarise the findings in this section
•
Smaller drivers receive a higher proportion of MAIS 2+ injuries than their
taller counterparts.
•
Small female drivers (up to 160 cm) are more frequently seriously injured than
male drivers of an equivalent height. In taller height bandings, male drivers
receive a higher proportion of MAIS 2+ injuries than female drivers.
•
Female drivers up to 160 cm in height have the highest proportion of MAIS
2+, AIS 2+ head, AIS 2+ abdominal and AIS 2+ leg injuries among the
classifications of height and gender presented in this section.
•
160 cm represents the 39th Percentile European adult female height.
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2.7.
Sept 2003
Population at increased risk
This section now goes on to compare the relative risk of serious injury in each of the
height bands to the standardised risk for the sample as a whole. Those areas where
there is an above average rate of serious injury can then be identified. Head injury
only is considered, as this is the only body region where significant results in terms of
a relationship between injury outcome and height have been found.
Recent work looking at the effectiveness of the driver’s airbag has shown this device
to be effective across the whole range of height and gender (kirk et al). Though the
smaller drivers are still most at risk of a serious head injury in the airbag fitted fleet,
the reduction in this risk is greatest for this group between airbag fitted and airbag not
fitted vehicles. This can be seen in figure 21.
Figure 21 Risk of AIS 2+ head injury by airbag fitment and height
non-equipped
equipped
0.35
Probability of AIS 2+ Head Injury
0.3
0.25
0.2
0.15
0.1
0.05
0
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2
2.1
Height (m)
On the basis of this result the advice is that smaller drivers should have a driver’s
airbag fitted. Thus, for this section looking at the risk of injury, the airbag fitted
vehicle population has been separated from the not fitted population. The height of the
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driver has again been banded, but with a finer banding of 5 cm. The probability of
injury across the range of heights has been compared to that for all drivers irrespective
of height and gender, called the ‘overall risk’. The results are displayed in figure 22.
Figure 22 Risk of AIS 2+ head injury by height
Fitted
Average Fitted
Not fitted
Average Not Fitted
Probability of AIS 2+ hea d injur
0.2 5
0.20
0.15
0.10
0.05
0.00
150
155
160
165
170
175
180
185
190
Height (cm)
Firstly considering vehicles not equipped with airbags, Figure 4 shows that drivers up
to 160 cm in height have a significantly increased probability of AIS 2+ head injury
above the average for such vehicles. This is supported by a Chi-square test, χ2 =
17.865, p=0.013, d.f=7. On the whole drivers of medium stature have a lower than
average probability of serious head injury. For the tallest drivers, over 185 cm in
height, the probability increases above the average.
The picture is slightly different for air bag fitted vehicles. It is clear from Figure 4 that
the probability of AIS 2+ head injury is lower for drivers of all statures in airbag fitted
vehicles than in those not fitted with airbags with one notable exception. In the 161165 cm height band the data suggests that there is a higher probability of AIS 2+ head
injury in an airbag fitted vehicle than in a non-airbag fitted vehicle. In airbag fitted
vehicles the probability of AIS 2+ head injury is above average for drivers up to 165
cm tall and also for those over 180 cm tall, whilst the probability of such injury is
below average for drivers between 166 and 180 cm tall. A Chi-square test shows
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Sept 2003
border line significant differences in the rate of injury for these three height groups in
airbag fitted vehicles. (χ2 = 5.722, p=0.057, d.f=2).
In summary, small drivers up to around 160-165 cm in height have an increased risk
of serious injury above the average for the entire sample irrespective of height. There
is also an increased risk for those tallest drivers in the sample.
2.8.
Detailed Injury Analysis
This section makes an in-depth case review of the serious head injury cases involving
shorter drivers. The aim is identify the specific injuries associated with any observed
increased risk of injury to small stature drivers and to review the cases to determine
whether or not proximity to the steering wheel / airbag module has significantly
influenced the injury outcome
The results of the previous analytical activities have shown that smaller stature drivers
are at a higher risk of injury than the average. However, for many body regions, this is
also the case for other sectors of the population. The clearest relationship between
injury outcome and height (and the only statistical significant relationship) is apparent
for head injuries where drivers up to 165 cm tall have a higher than average risk AIS
2+ injury. This is also the body region where we would expect to see, if anywhere, an
interaction with the airbag module. The actual number of cases representing the AIS
2+ injured drivers in this height range (up to 165 cm both male and female) is 8 and
these have been reviewed on a case by case basis. For comparison, the cases of AIS
2+ head injury for drivers between 166 and 180 cm tall (those below the average risk
of AIS 2+ head injury) have also been reviewed (7 cases).
The sub sample of eight "short" drivers is noteworthy for the severity of impact. It
includes three cases of impacts highly offset to the driver's side that resulted in severe
intrusion (B32389/2/1, W70547/1/1, W85432/1/1); two cases of under-running trucks,
with intrusion into the passenger compartment at head level (L12371/1/1,
B31965/1/1); and two cases of frontal impacts estimated at around 90-100 km/h
(B32483/1/1, W85502/1/1). In all there were five fatalities. Only one case could be
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regarded as non-catastrophic (H55410/2). Here the head injury is registered as a brief
loss of consciousness; however the driver is described as "blacking out" prior to
impact, and no bodily contact with the steering wheel, facia and so on is reported.
Therefore it is not entirely safe to assume that the loss of consciousness was traumatic
in nature, i.e. that it was a result of the impact.
The sub sample of seven "medium" drivers also features some severe impacts,
including two fatalities. There is a truck under-run with intrusion at head height into
the passenger compartment (W70258/1/1); and three cases where intrusion seems to
have played a significant role in the causation of injury (B31922/1/1, B32419/1/1,
H55825/1/1). That leaves three cases without intrusion where the influence of
occupant height on the causation and nature of injury can be investigated
(L12895/1/1, L13111/1/1, H55409/2/1). The head injury outcome in these three cases
did not extend beyond amnesia and brief loss of consciousness.
On the data currently available it is not possible to identify a systematic relationship
between occupant height and injury outcome or mechanism. The relevant sub sample
of airbag-fitted cases is dominated by the effects of intrusion and high impact
severity. Looked at from a different perspective, it could be surmised that airbags are
so effective that head fractures and brain lesions are now strongly associated with
"catastrophic" impacts. A clearer picture will emerge with the collection of further
CCIS cases.
Summaries of each of the cases follows
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2.8.1.
Sept 2003
CASE 85502/1/1
Driver in Peugeot 306 collided with on-coming BMW 318.
Occupant
36 y.o. female
165 cm
(5' 5")
65 kg
(10st 3lb)
BMI 23.9
seatbelt used
airbag deployed
Frontal impact
full frontal
12FDEW4
Delta-V
ETS
"short"
normal
Significant injuries
facial abrasions
brain injuries (subarachnoid, stem)
dislocated neck (atlanto-occipital)
# ribs
lung contusions
multiple # legs
AIS
1
6
2
3
4
2
91 km/h
83 km/h
Source of injury
header rail & non-contact
forces
steering wheel
facia & footwell
Comments
Fatal injuries - dead on arrival.
Intrusion into driver's area of passenger compartment.
Heavy bodily contact with frontal components.
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Ergonomics and Safety Research LTD
Assessment of Cars for Small Drivers
2.8.2.
Sept 2003
CASE W85432/1/1
Driver in Vauxhall Astra collided with on-coming Land Rover.
Occupant
30 y.o. female
158 cm
(5' 2")
76 kg
(12st 0lb)
BMI 30.4
seatbelt used
airbag deployed
Frontal impact
R offset frontal impact
01FDAW6
Delta-V
55 km/h
ETS
72 km/h
"short"
obese
Significant injuries
head lacerations and bruising
generalised brain swelling
lacerated aorta
transected thoracic spine
other internal chest & abdominal injuries
multiple severe leg fractures
# L arm
AIS
1
3
5
5
5
3
2
Source of injury
facia
steering wheel and facia
Comments
Fatal injuries - dead on arrival.
Significant intrusion on driver's side directly contributed to chest injuries.
PPAD 9/33/85 / VS1448
33
Ergonomics and Safety Research LTD
Assessment of Cars for Small Drivers
2.8.3.
Sept 2003
CASE W70547/1/1
Driver in Ford Fiesta collided into rear of Volvo HGV.
Occupant
66 y.o. male
165 cm
(5' 5")
77 kg
(12st 2lb)
BMI 28.3
seatbelt used
airbag deployed
"short"
overweight
Significant injuries
facial abrasions
multiple # skull
brain injuries
# sternum
# ribs
contused, lacerated lungs
ruptured aorta
bowel laceration
knee abrasions
# arm
Frontal impact
highly offset to R side
11FREW5
Delta-V
u/k
ETS
24 km/h
AIS
1
3
3
2
4
4
4
2
1
3
Source of injury
u/k1
seatbelt, steering wheel, &
possibly other contacts
facia
facia
Comments
Fatal injuries - died in casualty
Intrusion into driver's area of passenger compartment.
Heavy bodily contact into intruding frontal components.
1
attributed to airbag and own seat
PPAD 9/33/85 / VS1448
34
Ergonomics and Safety Research LTD
Assessment of Cars for Small Drivers
2.8.4.
Sept 2003
CASE H55410/2/1
Driver in Ford Mondeo collided with Volvo 440
Driver details
29 year old female
165 cm
(5' 5")
"short"
89 kg
(14st 0lb)
BMI 32.7
obese
Seatbelt used
Airbag deployed2
Vehicle details
frontal impact
12FDEW2
Delta-V
21 km/h
ETS
24 km/h
Injuries
Brief LOC
Whiplash
Chest bruising
Abdominal bruising
AIS
2
Source of injury
Attributed to airbag
Non-contact
Seatbelt
Seatbelt
Comments
Driver reportedly "blacked out" prior to impact. No further details.
Head injury could be due to prior condition.
Subject could have been out of position when airbag deployed.
2
coded as fitted/not deployed
PPAD 9/33/85 / VS1448
35
Ergonomics and Safety Research LTD
Assessment of Cars for Small Drivers
2.8.5.
Sept 2003
CASE L12371/1/1
Driver of Ford Courier that under-ran side of Mercedes HGV.
Occupant
50 y.o. male
165 cm
(5' 5")
100 kg
(15st 10lb)
BMI 36.7
seatbelt used
airbag deployed
Frontal impact
frontal under-run
12FDAA9
Delta-V
u/k
ETS
u/k
"short"
obese
Significant injuries
facial fractures
brain injury
arm fractures
AIS
3
3
3
Source of injury
intruding HGV
intruding HGV
Comments
Intrusion of HGV into passenger compartment at head level.
PPAD 9/33/85 / VS1448
36
Ergonomics and Safety Research LTD
Assessment of Cars for Small Drivers
2.8.6.
Sept 2003
CASE B32389/2/1
Driver in Peugeot 306 collided with on-coming Vauxhall Astra.
Occupant
43 y.o. female
152 cm
(5' 0")
54 kg
(8st 7lb)
BMI 23.4
seatbelt used
airbag deployed
Frontal impact
offset to driver's side
12FDEW3
Delta-V
28 km/h
ETS
23 km/h
"short"
normal
Significant injuries
LOC (GSC 8, briefly 3)
scalp lacerations
bilateral knee contusions
# R femur
# R arm
AIS
3
1
1
3
2
Source of injury
steering wheel
flying glass and airbag
facia
door
Comments
Intrusion into driver's area of passenger compartment.
Bodily contact with frontal structures, i.e. steering wheel (head) and facia (legs).
PPAD 9/33/85 / VS1448
37
Ergonomics and Safety Research LTD
Assessment of Cars for Small Drivers
2.8.7.
Sept 2003
CASE B31965/1/1
Driver in Daewoo Nexia collided head-on with oncoming Leyland HGV tipper
Occupant
64 y.o. female
163 cm
(5' 4")
weight u/k
BMI u/k
seatbelt used
airbag deployed3
Frontal impact
right offset; under-run
12FDEW8
Delta-V
unknown
ETS
unknown
"short"
Injuries
massive head injuries
AIS
4
massive injuries over rest of body
6
Source of injury
likely HGV intrusion at head
level4
steering wheel, facia, etc supported intrusion
Comments
Fatal injuries - dead on arrival.
Under-run and likely intrusion into passenger compartment at head height.
3
4
coded as fitted/not deployed
coded as unsupported contact with facia top
PPAD 9/33/85 / VS1448
38
Ergonomics and Safety Research LTD
Assessment of Cars for Small Drivers
2.8.8.
Sept 2003
CASE B32483/1/1
Driver in Rover 600 collided head-on at high speed with Rover 200.
Occupant
64 y.o. female
158 cm
(5' 2")
60 kg
(9st 6lb)
BMI 24.0
seatbelt used
airbag deployed
Frontal impact
severe frontal impact, L offset
12FDEW7
Delta-V
103 km/h
ETS
105 km/h
"short"
normal
Significant injuries
head abrasions
brain injury
# dislocation neck (C1)
# clavicle
# ribs
ruptured aorta
bilateral # knees
# legs
# R arm
AIS
1
3
6
2
5
5
2
2
2
Source of injury
u/k
u/k
seatbelt
facia, toepan
u/k
Comments
Fatal injuries - dead on arrival.
Intrusion on driver's side.
Bodily impact with frontal structures, possibly relevant to head injury.
PPAD 9/33/85 / VS1448
39
Ergonomics and Safety Research LTD
Assessment of Cars for Small Drivers
2.8.9.
Sept 2003
CASE 12895/1/1
Driver in Vauxhall Cavalier collided with bridge wall.
Occupant
38 y.o. male
180 cm
(5' 11")
83 kg
(13st 1lb)
BMI 25.6
seatbelt used
airbag deployed
"medium"
overweight
Significant injuries
Concussion
chest & abdominal bruising
Frontal impact
highly offset on left side
11FLEE4
Delta-V
47 km/h
ETS
47 km/h
AIS
2
1
Source of injury
steering wheel
seatbelt
Comments
Little or no intrusion into driver's area of passenger compartment.
PPAD 9/33/85 / VS1448
40
Ergonomics and Safety Research LTD
Assessment of Cars for Small Drivers
2.8.10.
Sept 2003
CASE L13111/1/1
Driver in Seat Alhambra collided with tree.
Occupant
31 y.o. female
168 cm
(5' 6")
57 kg
(9st 0lb)
BMI 20.2
seatbelt used
airbag deployed
"medium"
normal
Significant injuries
facial lacerations
amnesia
neck lacerations
Frontal impact
highly offset on L side
12FLAE6
Delta-V
u/k
ETS
u/k
AIS
1
2
1
Source of injury
top surface of facia
Comments
No intrusion in driver's area of passenger compartment.
Head contact with facia suggest forward seating position.
PPAD 9/33/85 / VS1448
41
Ergonomics and Safety Research LTD
Assessment of Cars for Small Drivers
2.8.11.
Sept 2003
CASE B31922/1/1
Driver in Rover 420 collided with tree.
Driver details
27 year old male
173 cm
(5' 8")
"medium"
56 kg
(8st 11lb)
BMI 18.7
"normal"
Seat belt used
Airbag deployed
Vehicle details
Frontal impact
12FDEW5
Delta-V
unknown
ETS
unknown
Injuries
AIS
1
3
2
3
3
2
3
1
facial lacerations
# base of skull
# cranium
multiple brain injuries
internal chest injury
internal abdominal injury
# femur
R leg lacerations
Source of injury
steering wheel
steering wheel
facia
Comments
Fatal injuries - died in casualty
Relatively severe impact, offset to left hand side.
Intrusion into driver's area.
Severe bodily contact into frontal structures, including head.
PPAD 9/33/85 / VS1448
42
Ergonomics and Safety Research LTD
Assessment of Cars for Small Drivers
2.8.12.
Sept 2003
CASE B32419/1/1
Driver in Peugeot 306 lost control and collided with on-coming Ford Fiesta.
Occupant
35 y.o. female
170 cm
(5' 7")
76 kg
(12st 0lb)
BMI 26.3
seatbelt used
airbag deployed
"medium"
overweight
Significant injuries
amnesia
bruised nose
chin abrasion
leg abrasions
Frontal impact
R offset frontal impact
01FDEW3
Delta-V
32 km/h
ETS
35 km/h
AIS
2
Source of injury
attributed to airbag
1
steering wheel; steering column
Comments
Some intrusion indicated on driver's side.
Light bodily impact with frontal structures, possibly relevant to head injury.
PPAD 9/33/85 / VS1448
43
Ergonomics and Safety Research LTD
Assessment of Cars for Small Drivers
2.8.13.
Sept 2003
CASE H55409/2/1
Driver in Ford Escort collided with unknown vehicle or other object
Driver details
60 year old male
178 cm
(5' 10")
"medium"
76 kg
(12st 0lb)
BMI 24.0
normal
Seat belt used
Airbag deployed
Injuries
LOC, 15-60 mins
# rib
# sternum
# right kneecap (patella)
Vehicle details
Frontal impact
12FDEW2
Delta-V
unknown
ETS
28 km/h
AIS
2
1
2
2
Source of injury
Attributed to airbag
Seatbelt
Facia
Comments
Kneecap injury indicates proximity to frontal components.
PPAD 9/33/85 / VS1448
44
Ergonomics and Safety Research LTD
Assessment of Cars for Small Drivers
2.8.14.
Sept 2003
CASE H55825/1/1
Driver in Vauxhall Astra crossed into path of oncoming Ford Transit.
Occupant
70 y.o. male
170 cm
(5' 7")
70 kg
(11st 0lb)
BMI 24.2
seatbelt used
airbag deployed
"medium"
normal
Significant injuries
facial lacerations
brain injury (subdural haemorrhage)
multiple # ribs
lacerated heart
leg abrasions
Frontal impact
full frontal impact
12FDEW5
Delta-V
u/k
ETS
54 km/h
AIS
1
4
3
3
1
Source of injury
steering wheel
steering wheel
facia
Comments
Fatal injuries -dead on arrival.
Collapse of passenger compartment on left side.
Intrusion into driver's area, especially at toepan.
Bodily contact with frontal structures
PPAD 9/33/85 / VS1448
45
Ergonomics and Safety Research LTD
Assessment of Cars for Small Drivers
2.8.15.
Sept 2003
CASE W70258/1/1
Driver in BMW collided head-on with oncoming DAF HGV
Occupant
22 y.o. male
177 cm
(5' 10")
90 kg
(14st 2lb)
BMI 28.7
seatbelt used
airbag deployed
"medium"
overweight
Injuries
massive head injuries
multiple # ribs (haemothorax)
bruised vein to heart (vena cava)
abdominal injuries
multiple # legs
multiple # arms
Frontal impact
right offset; under-run
12FZAW4
Delta-V
unknown
ETS
41 km/h
AIS
6
4
3
2
2
3
Source of injury
HGV
steering wheel
facia etc.
unknown
Comments
Fatal injuries - dead on arrival.
Uunder-run and intrusion into passenger compartment at head height.
PPAD 9/33/85 / VS1448
46
Ergonomics and Safety Research LTD
Assessment of Cars for Small Drivers
2.9.
Sept 2003
Recommendation for human factors assessment
The results from the data analysis have been used to identify that part of the driver
population who, from crashworthiness considerations, it is recommended should form
the group of ‘small drivers’ for consideration in the human factors assessment.
The analysis has shown that short drivers are at an increased risk of injury across most
body regions compared to their taller counterparts, but that there are also taller parts
of the population who show an increased risk above the average. This taller section of
the population warrants its own special consideration, not within the scope of this
project which is designed to assess the needs of small stature drivers.
The recommendation for the human factors assessment is based heavily upon the
results which are most statistically significant, that is for the findings with regard to
head injury. Considering figure 22 and categorising the height into short, medium and
tall based upon where the observed risk of injury falls above, below, and then again
above the overall risk, at the 5% level of significance, there is a difference in the
incidence of AIS 2+ head injury between the three groups with the short and tall
categories seeing an increased risk of AIS 2+ head injury above the medium category.
This is the case in both airbag fitted vehicles and those without airbags. For the short
category this equates to drivers below 165cm in height, that is 40th percentile adult
height. Taking this in conjunction with the apparent increase in risk of injury across
all body regions for those drivers up to 160 cm in height (23rd percentile adult height)
and keeping the focus on the ‘small driver’ it is recommended that human factors
assessment activities should target the entire lower quartile of the driver population,
that is drivers of 25th percentile height and below irrespective of gender.
PPAD 9/33/85 / VS1448
47
Ergonomics and Safety Research LTD
Assessment of Cars for Small Drivers
3.0
Sept 2003
Assessment of recommended chest to steering wheel distance
Secondary to the injury analysis, a further objective within the project has been to
determine guidelines, applicable to the UK car fleet, for the appropriate steering
wheel to chest distance for drivers of airbag fitted vehicles and to determine which
part of the population currently sit closer than this recommended distance. Is this part
of the population confined to the smallest stature drivers, or is seating position a
function of more than height alone? Are most members of the driving population able
to achieve at least the minimum recommended distance?
Some of these issues will be considered in the human factors assessment. The work
specification also allowed for a review of existing CCIS cases to enhance the
anthropometrical data and to establish the seating position of drivers in the accident
population. Additionally a review of the size of airbags in the UK fleet has been
undertaken, and estimates made for the amount of excursion a driver would make
during a frontal collision.
It was intended that information relating to seating position, injury outcome, size of
airbag and amount of excursion could in conjunction be used to evaluate a preferential
sternum to steering wheel hub distance that would minimise the risk of injury from
the deploying airbag in the event of an accident.
3.1.
Seating preferences and injury outcome for CCIS drivers
100 questionnaires requesting detailed anthropometrical measurements were sent out
to drivers who had been in an accident that was investigated as part of the CCIS data
collection procedure. An incentive of a £5 Boots voucher was offered for prompt
completion and return of the questionnaire.
The drivers were chosen from phase 6 of the CCIS, the most recent phase. These
drivers were more likely to still be at the same postal address and it was felt that it
would be better to target people with a more recent accident involvement than to
pursue too retrospective a follow up.
PPAD 9/33/85 / VS1448
48
Ergonomics and Safety Research LTD
Assessment of Cars for Small Drivers
Sept 2003
In accordance with the previous data analysis, only drivers who had been involved in
a single frontal impact were chosen. During the course of the CCIS investigation,
questionnaires are sent out to vehicle occupants requesting additional information.
Included within the questionnaire is an option to agree to or decline further contact
with the VSRC. For this follow up, drivers who had agreed to subsequent contact
were selected.
The study wished to examine the relationship between anthropometry, seating
position and injury outcome but also keep a focus on the smaller driver, thus a slight
bias towards shorter drivers was introduced into the data. In total 60 cases were
chosen so that the driver was 163 cm or shorter, the remaining 40 ranged from 168cm
to 193cm in height.
Table 3 shows the height distribution in the survey sample.
Table 3 Height distribution in survey sample
Valid
PPAD 9/33/85 / VS1448
1.47
1.50
1.52
1.53
1.55
1.57
1.60
1.63
1.68
1.70
1.73
1.75
1.78
1.80
1.83
1.85
1.88
1.90
1.91
1.93
Total
Frequency
1
1
1
1
2
18
16
20
1
4
7
5
6
4
8
1
1
1
1
1
100
Percent
1.0
1.0
1.0
1.0
2.0
18.0
16.0
20.0
1.0
4.0
7.0
5.0
6.0
4.0
8.0
1.0
1.0
1.0
1.0
1.0
100.0
49
Valid Percent
1.0
1.0
1.0
1.0
2.0
18.0
16.0
20.0
1.0
4.0
7.0
5.0
6.0
4.0
8.0
1.0
1.0
1.0
1.0
1.0
100.0
Cumulative
Percent
1.0
2.0
3.0
4.0
6.0
24.0
40.0
60.0
61.0
65.0
72.0
77.0
83.0
87.0
95.0
96.0
97.0
98.0
99.0
100.0
Ergonomics and Safety Research LTD
Assessment of Cars for Small Drivers
Sept 2003
The distribution of maximal injury severity for the drivers in the survey sample is
given below in table 4
Table 4 MAIS for drivers in sample survey
Severity
Percent
No Injury
6
Minor AIS 1
57
Moderate AIS 2
19
Serious AIS 3
18
The drivers were asked to record various anthropometric measurements relating to
arm length, leg length, and sitting height. They were then asked to assume their
normal driving position in their own vehicle and to measure the horizontal distance
between the centre of the steering wheel hub and their chest. Finally they were asked
to indicate the factors that influenced their driving position. A copy of the
questionnaire is included as Appendix 1.
A total of 32 questionnaires were returned. Of these, 5 in the sample no longer drove a
vehicle and so did not record a steering wheel to chest measurement. An
anthropometrical and injury analysis has been conducted on the remaining 27 cases.
Tables 5 and 6 give the height and injury severity for the cases included in the
analysis.
Table 5 Injury severity for questionnaire respondents
Severity
Percent
No Injury
3.7
Minor AIS 1
63
Moderate AIS 2
25.9
Serious AIS 3
7.4
PPAD 9/33/85 / VS1448
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Ergonomics and Safety Research LTD
Assessment of Cars for Small Drivers
Sept 2003
Table 6 Height distribution for questionnaire respondents
Valid
1.50
1.57
1.60
1.63
1.70
1.73
1.75
1.78
1.83
1.85
1.90
1.93
Total
Frequency
1
3
7
5
1
3
2
1
1
1
1
1
27
Percent
3.7
11.1
25.9
18.5
3.7
11.1
7.4
3.7
3.7
3.7
3.7
3.7
100.0
Valid Percent
3.7
11.1
25.9
18.5
3.7
11.1
7.4
3.7
3.7
3.7
3.7
3.7
100.0
Cumulative
Percent
3.7
14.8
40.7
59.3
63.0
74.1
81.5
85.2
88.9
92.6
96.3
100.0
The height distribution for the respondents is very similar to that for the 100 survey
cases. There are proportionally fewer serious injury cases among the respondents than
in the 100 case sample, but the proportion of moderate injury cases is higher.
The first analysis will look at the relationship between various anthropometrical
measures and proximity to the steering wheel.
Table 7 shows the summary statistics for the steering wheel to chest measurement.
Table 7 Summary statistics – Steering wheel to chest
Minimum Maximum
Steering wheel to chest
19 cm
42 cm
Mean
Standard Deviation
33.69 cm
5.75 cm
In total, three of the 27 respondents had a steering wheel to chest distance
measurement of 26cm or less, that is around 10 inches or below. Of these three
drivers, one is 150cm tall and recorded a steering wheel tot chest measurement of 26
cm. The other two are both 160 cm tall and recorded steering wheel to chest
measurements of 19 cm and 22 cm. The three driver who are 157 cm tall all achieved
much greater distances, 38cm, 39cm and 40cm.
PPAD 9/33/85 / VS1448
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Ergonomics and Safety Research LTD
Assessment of Cars for Small Drivers
Sept 2003
A linear regression has been performed on the dependent variable ‘steering wheel to
chest’ for each of the independent variables
•
Height
•
Sitting height
•
Leg length
•
Lower leg length
•
Upper leg length
•
Arm length
•
Lower arm length
•
Upper arm length
In each case the power of the regression, that is the strength of the linear relationship,
given by the regression coefficient R and the significance of the regression were
recorded. The results are given in table 8.
Table 8 Linear regression for dependent variable ‘Steering wheel to chest’
Independent variable
Regression coefficient (R) Significance (p)
Height
0.300
0.128
Sitting height
0.209
0.295
Leg length
0.316
0.108
Lower leg length
0.453
0.018
Upper leg length
0.136
0.498
Arm length
0.408
0.035
Lower arm length
0.419
0.029
Upper arm length
0.350
0.074
If there were a perfect linear relationship between the dependent and the independent
variable then the regression coefficient would be equal to 1. The significance of each
regression has been evaluated at the 5% level, thus if the p value is less than 0.05 then
the regression is significant. It is clear from the table that significant regressions exist
for three of the anthropometric measures taken, lower leg length, overall arm length
and lower arm length, these also have the largest regression coefficients amongst the
regressions undertaken.
PPAD 9/33/85 / VS1448
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Ergonomics and Safety Research LTD
Assessment of Cars for Small Drivers
Sept 2003
Figures 23,24,25 and 26 show the scatter plots and regression lines for the three
independent variables with significant regressions and also for interest that for overall
height.
Figure 23 Relationship between height and steering wheel to chest measurement
Measured
Predicted
Steering wheel to chest (cm)
45
40
35
30
25
20
15
145
150
155
160
165
170
175
180
185
190
195
200
Height (cm)
Figure 24 Relationship between lower leg length and steering wheel to chest
measurement
Measured
Predicted
Steering wheel to chest (cm)
45
40
35
30
25
20
15
40
45
50
55
60
65
70
Lower leg length (cm)
PPAD 9/33/85 / VS1448
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Ergonomics and Safety Research LTD
Assessment of Cars for Small Drivers
Sept 2003
Figure 25 Relationship between lower arm length and steering wheel to chest
measurement
Measured
Predicted
Steering wheel to chest (cm)
45
40
35
30
25
20
15
20
22
24
26
28
30
32
34
36
Lower arm length (cm)
Figure 26 Relationship between arm length and steering wheel to chest
measurement
Measured
Predicted
Steering wheel to chest (cm)
45
40
35
30
25
20
15
50
55
60
65
70
75
80
85
Arm length (cm)
In summary, in the sample of 27, lower leg length is the best indicator of steering
wheel to chest distance out of the variables available. This is followed by lower arm
length and total arm length. Height alone is not a good indicator of seating proximity.
PPAD 9/33/85 / VS1448
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Ergonomics and Safety Research LTD
Assessment of Cars for Small Drivers
Sept 2003
The next analysis will look at the relationship between injury outcome and the
distance between the steering wheel and the chest. The data has been banded in to
three groups according to steering wheel to chest distance. These are less than 30cm,
30-39 cm and 40cm or further. The small number of cases included in the analysis
does not allow for finer classification.
An important limitation in the data should be noted. It is currently prohibited within
the CCIS data collection protocol to send out a questionnaire to anyone who has been
involved in a fatal accident or to anyone who received severe head injuries. This has
obvious implications when looking at the overall injury outcome and that specifically
to the head. This is fundamentally disadvantageous when the analysis wishes to
determine the risk of particularly head injury in terms of proximity to the steering
wheel. However, as the review of CCIS cases revealed, there is no measure within the
CCIS data that indicates proximity and so no analysis is possible without additional
information being requested from the occupants.
Due to the small number of cases, rigorous statistical analysis is not possible, but
observations will be made based on the distributions.
Throughout the analysis the following severity definitions apply;
•
N/A = No injury
•
Minor = AIS 1
•
Moderate = AIS 2
•
Severe = AIS 3
Table 9 shows how MAIS (maximal AIS score across all body regions) is distributed
for the steering wheel to chest classifications.
PPAD 9/33/85 / VS1448
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Ergonomics and Safety Research LTD
Assessment of Cars for Small Drivers
Sept 2003
Table 9 Distribution of MAIS by steering wheel to chest measurement
Count
banded steering
wheel to chest
distance
< 30
30-39
40+
Total
Max. AIS score sustained by the occupant
N/A
Minor
Moderate
Serious
4
1
9
5
2
1
4
1
1
17
7
2
Total
5
16
6
27
There is no evidence within the table to suggest that those drivers sitting closer to the
steering wheel had a more serious overall injury outcome than those sitting further
away.
Table 10 shows how head (cranium) injury and neck (including cervical spine) injury
severity is distributed for the steering wheel to chest classifications.
Table 10 Distribution of Head and Neck severity by steering wheel to chest
measurement
Count
banded steering
wheel to chest
distance
Total
< 30
30-39
40+
Max. AIS sustained within Head
(cranium) or Neck (inc.cervical
spine) region, as defined by ISS
system
N/A
Minor
Serious
2
3
11
4
1
5
1
18
8
1
Total
5
16
6
27
It could be argued from table 10 that there is an over representation of minor injuries
within the < 30 cm steering wheel to chest distance category. However, this is merely
an observation and can not be supported statistically.
For head and neck injury a further distinction has been made by airbag deployment.
The results are shown in table 11. Again, with the small number of cases available and
the absence of severe head injury cases it is difficult to form a conclusion regarding
any adverse airbag deployment. It does however not appear to be the case in this
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limited sample that drivers sitting closer to the steering wheel have an increased level
of serious injury to the head or neck region than those sitting further away.
Table 11 Distribution of Head and Neck severity by steering wheel to chest
measurement and airbag deployment
Count
The activation of an
airbag in the
steering wheel hub
N/A
activated
banded steering
wheel to chest
distance
< 30
30-39
40+
Total
banded steering
wheel to chest
distance
< 30
30-39
40+
Total
Max. AIS sustained within Head
(cranium) or Neck (inc.cervical
spine) region, as defined by ISS
system
N/A
Minor
Serious
2
1
3
2
1
4
1
9
4
1
2
8
2
1
9
4
Total
3
6
5
14
2
10
1
13
Table 12 shows how chest (including thoracic spine) injury severity is distributed for
the steering wheel to chest classifications.
Table 12 Distribution of chest severity by steering wheel to chest measurement
Count
banded steering
wheel to chest
distance
Total
< 30
30-39
40+
Max. AIS sustained within Thorax
(inc. thoracic spine) region, as
defined by ISS system
N/A
Minor
Moderate
4
1
11
5
5
1
20
2
5
Total
5
16
6
27
The only AIS 2 injuries sustained were to those drivers in the middle distance
category, that being 30-39 cm between the chest and the steering wheel.
Table 13 shows how abdominal (including lumbar spine) injury severity is distributed
for the steering wheel to chest classifications.
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Table 13 Distribution of chest severity by steering wheel to chest measurement
Count
banded steering
wheel to chest
distance
Max. AIS sustained
within Abdomen (inc.
lumbar spine) region,
as defined by ISS
system
N/A
Minor
5
15
1
6
26
1
< 30
30-39
40+
Total
Total
5
16
6
27
In this sample, there is only a single AIS 1 abdominal injury and that was suffered by
a driver with a chest to steering wheel measurement of 32 cm. Again, in the limited
sample there is nothing to suggest that proximity has an effect on injury outcome to
the abdomen.
Finally table 14 shows how lower extremity (including the pelvic region) injury
severity is distributed for the steering wheel to chest classifications.
Table 14 Distribution of chest severity by steering wheel to chest measurement
Count
banded steering
wheel to chest
distance
Total
< 30
30-39
40+
MAx. AIS sustained in the leg and
pelvis region
N/A
Minor
Moderate
3
1
1
4
9
3
3
2
1
10
12
5
Total
5
16
6
27
For leg and pelvic injury, those in the middle chest to steering wheel category appear
to have a higher proportion of injuries than those sitting closer or further away. It is
not evident within the sample that those sitting closest to the steering wheel have a
higher rate of serious injury than those sitting further away.
The work presented in this section could be seen as a useful pilot study using the
CCIS data and additional retrospective data collection to address issues concerning
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proximity and injury outcome. The CCIS data has the benefit of detailed injury and
vehicle variables whilst the follow up to request additional anthropometrical
measurements resulted in a 32% response rate. This response rate is favourable in
terms of survey sampling but for the purposes of this study resulted in just 27 cases
suitable for analysis. A larger survey would enable more conclusive results to be
obtained. The main limitation, discussed previously, is the current CCIS
questionnaire protocol which does not permit cases where the driver had a severe head
injury or where fatalities were involved to be pursued. There may, in the future, be
some way of overcoming this limitation.
The study has revealed some useful indications regarding the relationship between
anthropometry and proximity to the steering wheel and has shown that height alone
does not appear to be the best indicator of how close a driver will sit to the steering
wheel.
3.2.
The NHTSA recommendation
The following passage is quoted from the NHTSA website http://www.nhtsa.dot.gov/. It
provides an explanation for their recommended 10 inch chest to steering wheel hub
distances for drivers of cars fitted with a driver’s airbag.
“NHTSA is recommending 10 inches as the minimum distance that drivers should
keep between their breastbone and their air bags for several reasons. First, the agency
believes that drivers who sit 10 inches away and buckle up will not be at risk of
serious air bag injury. Drivers who can maintain that distance will be much safer if
they keep their air bags on. The 10-inch distance is a general guideline that includes a
clear safety margin. IIHS recommended the same distance in its comments. The 10inch distance ensures that vehicle occupants start far enough back so that, between the
time that pre-crash braking begins and time that the air bag begins to inflate, the
occupants will not have time to move forward and contact the air bag until it has
completed or nearly completed its inflation. The 10 inch-distance was calculated by
allowing 2-3 inches for the size of the risk zone around the air bag cover, 5 inches for
the distance that occupants may move forward while the air bags are fully inflating,
and 2-3 more inches to give a margin of safety. The 5-inch rule of thumb commonly
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used in air bag design is described in the paper, "How Airbags Work (Design,
Deploying Criteria, Costs, Perspectives)" presented by David Breed at the October
19-20, 1992 Canadian Association of Road Safety Professional International
Conference on Airbags and Seat Belts. Second, the agency is focusing attention on the
10-inch distance because it wants drivers to strive to get back 10 inches. NHTSA
believes that almost everyone can achieve at least 10 inches and get the extra margin
of safety that comes from sitting that far back. See the July 1997 survey submitted by
IIHS. However, some drivers who cannot get back a full 10 inches will still be safer,
on balance, if they are protected by their air bag. The nearer that these drivers can
come to achieving the 10-inch distance, the lower their risk of being injured by the air
bag and the higher their chance of being saved by the air bag. Since air bag
performance differs among vehicle models, drivers may wish to consult their vehicle
manufacturer for additional advice. NHTSA considered an alternative suggestion by
Ford in a late August 1997 meeting with the agency that the 10-inch distance be
measured from the air bag to the chin instead of the breastbone. The agency has
decided to use the breastbone as the measuring point because of the greater safety
margin provided.”
The explanation given here follows a logical argument based around a known
aggressive phase of deployment (first 2-3 inches), allowing for an amount of occupant
excursion prior to the deployment phase (5 inches) and a further safety margin
bringing the total to 10 inches. Each of the elements comprising the 10 inches is
justifiable, but there seems to have been a certain amount of ‘common sense’
employed when putting these elements together as a whole. A further literature search
has been conducted in order to establish if a more scientific derivation for this
guideline exists but this has not revealed any such published document.
There also remains the fact that the NHTSA recommendation was derived for use by
the American public whose available car fleet differs from that in the UK. Thus it was
considered necessary to make a review of the 10 inch guideline and its applicability to
the UK car fleet in order that the UK government could make the best informed
decision with regards to advice to the public. This has been undertaken through a
finite element modelling activity, the results of which are reported in section 5.
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4.0
Human Factors Assessment
4.1.
Literature Review – Drivers’ positioning within the car
The vehicle is a complex environment and the human being is expected to interact
with many components of it, both interior and exterior. The vehicle design process
therefore needs to take into account a variety of complicated user-requirements in
order to optimise driver performance.
One important aspect of vehicle design involves the seating position of the driver. The
driver’s seat has been described as a ‘work-chair’ that must fulfil ergonomic
requirements for good and safe driving. Ergonomic observations indicate that the
driver normally maintains a very static sitting posture whilst effectively undertaking a
continuous ‘vigilance’ task (Grandjean, 1980). In a practical sense, driving comfort is
achieved through a combination of adjustments in three design elements of
vehicle/occupant packaging consisting of the seat, pedals and the steering wheel.
From this perspective, the optimal driving posture is derived by positioning eye point,
accelerator heel point, steering wheel point and hip point (Grandjean 1980).
The design of the vehicle interior depends on the physical constraints of the human
being. The distances for comfortable arm reach (for control switches, steering wheels
and other interior features) and leg reach (for pedals) will influence where such items
are located within the interior. Obviously, such items should be located where they are
easily accessible and not beyond reach to even the smallest driver. An SAE ‘Controls
Reach Study’ was undertaken to establish a general model for reach boundaries for
driver reach and operation of control. Leiser and Carr (in Richardson, 2001) suggest
that due to the biomechanical and anthropometric characteristics of people, primary
controls should be located centrally in front of the driver in an area 300mm high by
600mm wide, increasing to 900mm by 900mm to accommodate secondary controls.
Since the distance for comfortable reach varies from person to person, many designs
are now adjustable, including steering wheels. Figure 27 below shows the basic
principle for the driver. It illustrates that the primary controls (i.e. the steering wheel
and the pedals) are located in such a way so as to ensure that the driver can maintain a
comfortable posture whilst using them. It has been suggested that as the driver is
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effectively ‘working’ whilst driving, the posture of the driver whilst ‘working’ needs
to be considered. Therefore, when considering the design of a vehicle seat, the
positioning of controls and the ‘determined’ posture of the ‘working’ driver should be
borne in mind (Rebiffe, 1980).
Figure 27: Source: Richardson (2001)
Van Cott and Kinkade (1972) also propose a set of design features for vehicle cabs
suitable for persons between the 5th and 95th percentiles as illustrated in figure 28
Their recommendations include specified dimensions and the important features
include the seat height, depth, back angle, fore and aft adjustability of the seat, leg and
knee clearance, location of hand and foot controls and visual field.
When designing the driver environment within a vehicle, perhaps the most important
issue for consideration is that of body dimensions. There is wide variation between
members of the driving population and to reflect this, the seat itself may be designed
such that it can be optimally adjusted to cover the range from the 5th to the 95th
percentile of the relevant population characteristic. However, this presents inherent
problems. For example, Bittner (1974) found that in one situation, the 95th and 5th
percentiles on each of 13 dimensions would exclude 52% of the population, instead of
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the 10% implied by the 95th and 5th percentile limits of individual dimensions. To
illustrate this point, because of poor correlation between body dimensions, it does not
necessarily follow that a male adult who is in the 95th percentile height range has leg
lengths in the corresponding 95th percentile. The location of a foot control is therefore
not simply a function of leg length; it is a combined function of such factors as leg
strength, lower leg length, upper leg length and ranges of movement at the hip, knee
and ankle. It is also influenced by seat height, which in turn is derived from seated eye
level and other dimensions.
Figure 28: A Set of Design Features for Vehicle Cabs Source: Van Cott and Kinkade
(1972)
Research in the UK has in fact shown that the 5th percentile UK female sits some
21.5cm closer to the hub of the steering wheel than the 95th percentile male (Parkin et
al, 1993, figure 1; Cullen et al, 1996). In the same series of studies, 5th%ile females
were found to sit 9.2cm closer to the steering wheel than the surrogate 5th percentile
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dummies. Even 50th percentile female drivers were found to sit 6.2cm further forward
than their male counterparts – refer to Figure 29.
Figure 29: UK Driver’s Sitting Position Compared with Hybrid III Dummies
Source: Parkin et al, 1993
Note:
Head outlines indicate drivers’ sitting positions and black dots indicate naison
positions for comparable dummies
McFadden et al (2000) studied some 300 Australian drivers (150 males and 150
females) and found that on average, women sat 4 to 5 cm closer to the steering wheel
than did men and also that the 5th-percentile female sat between 12 and 15cm closer to
the steering wheel than the 50th-percentile male driver. The greatest discrepancy in
dimensions between males and females was found to be the distance between the
driver’s sternum and the centre of the steering wheel. They also found that the height
of the driver was the most important determinant of driver distance from the steering
wheel. On average, for every 10cm increase in height, the driver sat at least 3cm
further away from the steering wheel. Height of driver and size of car were also found
to affect driver’s head and chest positioning from the centre of the steering wheel.
These distances increased with the height of the driver and decreased with increasing
size of the car. Drivers of large cars sat approximately 2cm closer to the steering
wheel than did drivers of small cars.
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Clearly, designing a single seat that will fit every driver is near impossible.
Furthermore, the implications of designing the vehicle environment for a particular
population range present a number of safety challenges (in addition to anthropometric
issues) that may not be immediately evident. For example, by designing the
environment to ensure that the 5th to 95th percentile range is covered, it is often
assumed that it is best to optimise for a 50th percentile person. When vehicle safety
regulation compliance testing is undertaken, it is normally the 50th percentile
anthropomorphic test dummy (representing an ‘average’ person) that is used in the
test procedure to assess the risk of injury and vehicle ‘crashworthiness’. However,
although the 50th percentile dummy response may indicate that the vehicle complies
with the relevant crashworthiness regulations (as far as the ‘average’ person is
concerned), there may a tendency to overlook the fact that the vehicle was not tested
using crash-dummies that represent the population extremes once the regulatory
compliance obligation has been fulfilled. Also, there is continuing disagreement as to
whether dummy response is a true predictor of human response. Such issues may in
turn have a detrimental effect on those population extremes in real-world situations.
4.2.
Human factors assessment objectives
In light of this research and the findings from phase 1 of increased risk to small
drivers, the research objectives of phase two of this project are:
•
To determine the reasons behind the seating attitudes of smaller drivers,
•
To develop and assess vehicle modifications / design countermeasures to
address the increased risk of injury.
To meet these objectives this phase has been sub-divided into three activities:
•
Anthropometric analysis of adults with small stature,
•
Exploration of the positions adopted by small drivers,
•
Consideration of counter measures and remedial actions.
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A description of the activities undertaken within each of the activities above and the
findings resulting from them are discussed in the following sections.
4.3.
4.3.1.
Anthropometric analysis of adults with small stature
Aim
As the follow up of CCIS cases reported in section 3 has shown, the classification of
drivers by stature alone is inadequate for a thorough understanding of preferred seat
position. The trunck, leg length and reach of small drivers can all vary significantly
and each variable is likely to influence the quality of the position adopted. The aim of
this activity is to identify and quantify further pertinent aspects of the anthropometry
of the small driver group.
4.3.2.
Anthropometric research data
Based on the research described in section 3 and the experience of the transport
ergonmists with the project team, it was considered that the following anthropometric
measures would be of particular relevance:
•
Upper arm length
•
Lower arm length
•
Upper leg length
•
Lower leg length
•
Sitting eye height
Whilst there are numerous sources from where numerical values for the above
measure may be obtained, it is important that the appropriateness of these sources is
considered. Since our aim is to estimate the numerical values for the UK small driver
population, the samples upon which existing anthropometric data tables are based
should align as closely as possible to our population to maximise accurate
representation. For instance surveys which were:
•
conducted several decades ago,
•
drawn from a different target population e.g. army personnel,
•
based on a non-UK population,
may have limited applicability.
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Relatively recent anthropometric data based on the general UK adult population is
likely to provide a good starting point. Such data and its sources are given in Table
15.
Further investigations were made to determine if such data existed which:
•
specifically concerned the UK driver population,
•
related the values of anthropometric dimensions to each other since it
cannot be assumed that a person of 5th percentile stature will necessarily
have 5th percentile limb lengths.
The investigations revealed that a major study in this area was undertaken by the
Motor Industry Research Association MIRA in 1976 (Haslegrave 1979) which
surveyed 2,000 drivers on the following 15 anthropometric measurements:
•
Eye height
•
Shoulder height
•
Neck width
•
Shoulder width
•
Chest breadth
•
Seat breadth
•
Chest depth
•
Stomach depth
•
Thigh depth
•
Knee height
•
Buttock-knee length
•
Arm length
•
Shoulder-elbow length
•
Elbow-fingertip length
•
Shoulder slope
Using this data, it was possible to define UK male and female driver percentile values.
However the author, recognising that anthropometric dimensions are not well
correlated, used the data that had been obtained to generate models for 5th percentile
female and 95th percentile male drivers. The models defined the drivers in terms of
their stature i.e. 5th and 95th percentiles, and then assumed that all other dimensions
were the mean average for that height. The resultant values for these models are
given in Table 16 below.
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Table 15: Sources of UK adult anthropometric data
Relevant
anthropometric
measures (mm)
Stature
Sitting eye height
Upper arm length
Lower arm length
Upper leg length
Lower leg length
Female
5th%ile
50th%ile
Male
95th%ile
5th%ile
50th%ile
95th%ile
Pheasant Peoplesize Pheasant Peoplesize Pheasant Peoplesize Pheasant Peoplesize Pheasant Peoplesize Pheasant Peoplesize
1988
1998
1988
1998
1988
1998
1988
1998
1988
1998
1988
1998
1505
685
300
400
520
455
1514.4
687.6
312.5
396.3
521.4
450.3
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1610
740
330
430
570
500
1620
741.9
341.5
431.1
588.9
493.9
1710
795
360
460
620
540
- 68 -
1725.6
796.3
370.6
465.9
656.4
537.4
1625
735
330
440
540
490
1641
742.8
346.6
442
552.2
497.8
1740
790
365
475
595
545
1755.1
803.4
376.7
477
612.6
544.4
Ergonomics and Safety Research Ltd
1855
845
395
510
645
595
1869.2
864.1
406.7
512.1
673
591.1
Table 16: Anthropometric dimensions for the driver modules generated by
Haslegrave (1979)
Eye height
Shoulder height
Neck width
Shoulder width
Chest breadth
Seat breadth
Chest depth
Stomach depth
Thigh depth
Knee height
Buttock-knee length
Shoulder-elbow length
Elbow-fingertip length
Stature
Weight
Driver models
5th percentile female
95th percentile male
724 mm
844 mm
548 mm
657 mm
128 mm
144 mm
328 mm
382 mm
281 mm
319 mm
352 mm
387 mm
257 mm
249 mm
258 mm
266 mm
155 mm
165 mm
510 mm
603 mm
568 mm
651 mm
331 mm
402 mm
402 mm
500 mm
1537 mm
1851 mm
58.00 kg
82.60 kg
However this model cannot be fully applied to this project since it does not include
males under 1600mm and females between 1537 and 1600mm. As a means of
investigating small driver anthropometry further, a survey of 100 small drivers
(1600mm or less) was undertaken as part of the project and is described below.
4.3.3.
Anthropometric survey
In addition to the review of relevant anthropometric research data, a survey of one
hundred small drivers was undertaken – this is discussed in greater detail in section
4.4.
The basis for selection as a small driver was the requirement that the participant had a
stature of 160cm or less. This equated to the smallest quartile in stature of the UK
population, which was defined in phase 1 as the population of small drivers.
The participants were drawn from ICE Ergonomics database and were also recruited
from the local area. The sample consisted of 4 men which was considered to reflect
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the relative proportion of males to female in the UK population for individuals of this
stature.
For each participant their stature, sitting eye height and upper/lower arm and leg
lengths were recorded and converted into percentiles based on female data obtained
from Peoplesize. Based on the survey, the profile of the UK small driver is given in
Table 17 below.
Table 17: Small driver profile based on survey results
Actual measurements (mm) Percentile values (%ile)
4.3.4.
Min
Mean
Max
Min
Mean
Max
Stature
1400
1550
1620
1
14
50
Sitting eye height
650
762
900
1
1
88
Upper arm length
220
266
330
n/a
n/a
n/a
Lower arm length
200
235
330
1
6
99
Upper leg length
470
539
630
1
4
32
Lower leg length
420
483
550
1
1
72
Conclusions
To summarise, research indicates that the optimal driving position is dependent upon
eye location and reach to the steering wheel and pedals. This suggests that sitting eye
height and upper/lower arm/leg lengths would be relevant to determining the seated
position adopted by small drivers.
Unfortunately little previous research specifically concerning the anthropometry of
small drivers was identified, although anthropometric data pertaining to the UK
population as a whole and to UK drivers in particular was obtained for review.
A model for the 5th percentile female driver was developed by Haslegrave (1979) and
may be used as an approximation to the small driver population of interest to this
project (refer to shaded area of table 18 below); measurements based on a survey
sample of 100 drivers undertaken within this project are also shown in the table.
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Table 18: Small driver profile – Comparative data
Haslegra
Vehicle Safety Research Centre
ve
Actual measurements
Percentile values
(mm)
(%ile)
Min
Mean
Max
Min
Mean
Max
Stature
1537
1400
1550
1620
1
14
50
Sitting eye height
724
570
661
780
1
1
88
Upper arm length
331
220
266
330
n/a
n/a
n/a
Lower arm length
402
200
235
330
1
6
99
Upper leg length
568
430
517
570
1
4
32
Lower leg length
510
290
407
510
1
1
72
4.4.
Exploration of the positions adopted by small drivers
It was felt that the positions adopted by small drivers could only be properly explored
by scrutinising the true behaviour of individuals in the real-world. Accordingly, a
sample of small drivers was recruited and their preferences recorded.
4.4.1.
Aim
In order to identify the driving positions adopted by small drivers and the rationale for
this, a survey of 100 small drivers (as defined in phase 1), was undertaken. The
survey was designed to specifically identify:
•
The position adopted and the drivers’ reason for adopting that position,
•
The driver’s access to primary and secondary controls,
•
The quality of the driver’s view of the road,
•
The driver’s knowledge of the range of driving position adjustment
available on their own vehicle,
•
The driver’s views on the adequacy of their adjusted position and the
importance of driving position in determining the selection of their vehicle,
•
The driver’s awareness of the potential hazard presented by a close seating
position.
In addition to the above considerations, it was also decided to assess how far back
participants could position themselves whilst still being able to reach the primary
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controls. This was to investigate if, given the correct education, drivers could
physically improve their margin of safety in their existing vehicles.
4.4.2.
Methodology
One hundred small drivers were self selected following publicity throughout the local
area. The only criteria were that they regularly used a vehicle and that they were a
maximum of 160 cm in height. The participants were individually invited to attend
ESRI LTD premises in their own vehicle for a period of approximately 90 minutes,
for which a small remuneration was made.
Each driver was greeted and evaluated by a pair of researchers, drawn from a team of
three, to ensure data collection consistency. In each case there was one male and one
female researcher to ensure compliance with ethical requirements.
Initially the basic principles of the study were explained, although reference to safety
or specific areas of interest were withheld, before the participants were asked to
complete an agreement to take part in the study. Simple static anthropometry
measurements were then taken. These were collected with each driver positioned on
the same chair and dressed without outerwear of shoes. A note was made of the size
of the shoe heel.
The driver was then escorted to their own vehicle, in which they had arrived and
details of the vehicle recorded. In this manner the seating position was unaltered from
their norm and would reflect their chosen posture. Basic dimensional measurements
of this position were recorded before the driver was asked to sit in the vehicle. Once
installed, further anthropometric data was collected which would facilitate
examination of the fit of the driver to the vehicle.
In addition to the anthropometric data, certain other data was recorded. This included
the vision from the vehicle and some qualitative data regarding the participant’s
knowledge of, and satisfaction with, the seating provision. Their vehicle purchase
priorities were also examined as was their knowledge of airbag safety requirements.
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The participant was then required to adjust the seating so that they were as far as
practicably possible from the controls whilst still able to control the vehicle. This
position was standardised by asking the subject to start from a position where the seat
was at its rearmost location and then to slide the seat forward until the accelerator
pedal could be fully depressed. Using the accelerator ensured that manual and
automatic vehicles received the same treatment. The participant was then asked to
alter the other seat adjusters such that they could just control the vehicle.
Once this was completed a duplicate set of measurements were taken to allow for
comparison with the standard seating position. The two seating positions were
referred to as ‘normal’ and ‘alternative’. Photographic records were made of each
adopted posture.
Once the data had been collected from the participant’s car, they were invited to
repeat the exercise in a reference vehicle. This was a 2000 model Peugeot 306,
chosen as representative of a popular small hatchbacks. Again, normal and alternative
posture information was recorded and photographic record made. The relevant
qualitative data was also recorded.
Once all the data had been collected it was collated into a Microsoft Excel spread
sheet to permit interrogation. This data was validated by manual inspection and
provides the basis for following the evaluation.
Following the collection of data on small drivers it was felt that there would be benefit
in recording similar information for a small sample of randomly selected drivers, who
could provide a normative reference. Accordingly, a further 22 drivers were
evaluated who were drawn from the general driving population. The data from this
group was collected in an identical manner and is presented alongside the small driver
data in the following sections.
Sample specification
The basis for selection as a small driver was the requirement that the participant had a
stature whose stature is in the order of 160cm or less. This equated to the smallest
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quartile in stature of the UK population which was defined in phase 1 as the
population of small drivers.
The participants were drawn from ESRI LTD database and also recruited from the
local area. The sample consisted of 4 men which was considered to reflect the
relative proportion of males to female in the UK population for individuals of this
stature.
Data collected
Refer to Appendix 2 for the data collected, which contains a copy of the data
collection form.
4.4.3.
Results
The data collected from the survey is presented in the following sections. In each
case the drivers under the 160 cm threshold are referred to as ‘small drivers’ whilst
the normative reference group are referred to as ‘normal’. Where appropriate
graphical figures are provided to aid interpretation of the data, and a short summary of
the implications is presented.
Participant details
The general participant and vehicle details are given in the Tables 19 to 25.
Table 19: Driver gender
SAMPLE GROUP
MEN
WOMEN
Small drivers
4
96
Normal
12
8
The gender mix is representative of the small stature requirement, with 96% of the
small drivers being women. The normal population, however, are more equally
balanced with 40% of this group being women.
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Table 20: Driver stature
STATURE
MINIMUM
MEAN
MAXIMUM
[STATURE %ILE]
CM (FT)
CM (FT)
CM (FT)
SMALL
140 (4’ 7”)
154 (5’ ½”)
162 (5’ 4”)
DRIVERS
[0.03]
[5.4]
[26.5]
NORMAL
161 (5’ 3”)
175 (5’ 9”)
193 (6’ 4”)
POPULATION
[23.1]
[72.8]
[99.7]
The driver stature details illustrates that for the small driver population, the largest
driver approximated to 25th percentile of the whole adult driving population, as
anticipated, whilst the mean small driver stature approximated to the 5th percentile
adult. Accordingly, this population suitably reflects the smallest individuals normally
included in good design practice.
The normal population are considerably larger, with the mean representing 73rd
percentile adult height and the tallest exceeding the 99th percentile. This partly
reflects the small sample size, but ensures that the data collected from this group will
clearly identify differences between small and large drivers seating positions.
The ages of the participants were spread across the general driving population, and
permitted consideration of limitations based on age as well as preference.
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Table 21: Driver age
AGE (YEARS)
MINIMUM
MEAN
MAXIMUM
19
40
67
21
35
53
MINIMUM
MEAN
MAXIMUM
SMALL
DRIVERS
0.5
18.5
47
NORMAL
POPULATION
1
16
35
SMALL
DRIVERS
NORMAL
POPULATION
Table 22: Driver experience
EXPERIENCE
(YEARS)
Driver experience is important, since vehicle control and good posture are learned
experientially. Whilst there were some novice drivers, the mean driving experience of
18.5 years for small drivers and 16 years for normal individuals indicates that
preferences will be firmly established.
Table 23: Car ownership
OWNER (YEARS)
MINIMUM
MEAN
MAXIMUM
SMALL DRIVERS
0.25
2.7
15
0.25
2.1
6
NORMAL
POPULATION
As with driver experience, exposure to a car model will reinforce the chosen posture.
Mean car ownership in excess of 2 years for both groups, and a minimum 3 months
ownership ensured familiarity.
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Table 24: Car access and use
CAR USE
OWN
SHARED
OTHER
SMALL DRIVERS
77
11
12
21
0
1
NORMAL
POPULATION
The majority of participants owned the vehicle they drove. The remainder shared it
with a partner or borrowed it from a family member.
Table 25: Vehicle specification
SMALL DIVERS
OWN VEHICLE
19 MAKES
59 MODELS
AGE OF VEHICLE
OLDEST 1966
YOUNGEST 2002
TRANSMISSION
92 MANUAL
8 AUTOMATIC
NORMAL POPULATION
OWN VEHICLE
14 MAKES
20 MODELS
AGE OF VEHICLE
OLDEST 1972
YOUNGEST 2001
TRANSMISSION
19 MANUAL
3 AUTOMATIC
STANDARD VEHICLE PEUGEOT 306 (2000 MODEL)
A wide diversity of vehicles were represented by the sample groups. Over 60 models
covering in excess of 20 makes ensured that a cross section of automotive design
practices were accommodated. The inclusion of vehicles of considerable age
provided an interesting counterpoint to the modern vehicle fleet whilst the inclusion
of some automatic transmission vehicles ensured that postures driven by reach to
clutch and gear lever alone were not exclusively considered.
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The driving position adopted
The driving position adopted was measured for the driver’s own car (referred to as
‘own’) and the reference car (referred to as ‘ref’). Where appropriate, the minimum,
mean and maximum dimension are recorded as data to illustrate the diversity of
individuals, whilst mean values only are used in graphical depictions for clarity.
For the purposes of illustration, some example photographs are presented. Figure 30
shows the diversity of postures, with a very small subject sitting some distance from
the steering wheel whilst a taller subject sitting much closer.
Figure 30: Diversity of seating positions
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Figure 31 shows the four male drivers who were part of the smaller driver population.
Figure 31: Male drivers in the smaller driver population
Figure 32 shows an example of the comparison between the ‘normal’ driving position
on the left and the ‘adjusted’ driving position on the right.
Figure 32: Normal (left) and adjusted (right) driving positions
Figure 33 shows that older cars often have similar driving positions to more modern
variants. The vehicle on the left is 1966 registered, whilst that on the right is 34 years
younger.
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Figure 33: Vehicle age may not alter driving position
General seating measures
The general seating measures relating to the preferred seating position selected are
give in Table 26 and 27. These data illustrate the overall relationship of the individual
to the vehicle for both their own and the reference vehicle.
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Table 26: General seating measures for small drivers
GENERAL SEATING
OWN
OWN
OWN
REF
REF
REF
MEASURES (CM)
MIN
MEAN
MAX
MIN
MEAN
MAX
101
120.1
155
112
118.2
125
94
112.0
146
104
110.1
118
20
35.9
48
23
32.6
49
2
4.7
8
2
4.7
8
28
40.6
53
28
39.4
51
ELBOW ANGLE
80
121.7
180
85
123.6
180
HIP ANGLE
80
111.1
150
90
112.8
150
KNEE ANGLE
80
121.6
155
95
120.2
150
FOOT ANGLE
70
103.8
130
80
103.5
130
6
17.9
32
7
19.1
26
0
5.3
18
0
4.2
13
SITTING HEIGHT TO
GROUND
SITTING EYE
HEIGHT TO GROUND
STEERING WHEEL
TO CHEST
CHEST CONTACT
POINT (1 - 9)
STEERING WHEEL
TO NASION
HEADREST TO TOP
OF EARS
BACK OF HEAD TO
HEADREST
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Table 27: General seating measures for normal drivers
GENERAL SEATING
OWN
OWN
OWN
REF
REF
REF
MEASURES (CM)
MIN
MEAN
MAX
MIN
MEAN
MAX
119
128.6
166
118
123.3
128
112
121.0
160
103
115.0
120
29
40.6
51
34
41.6
48
2
4.6
5
2
4.7
8
40
47.5
57
38
47.5
54
ELBOW ANGLE
110
143.4
180
130
149.3
180
HIP ANGLE
100
113.6
140
105
115.9
140
KNEE ANGLE
100
125.9
140
115
126.8
145
FOOT ANGLE
85
100.5
120
95
104.1
115
15
63.4
-
14
18.7
28
0
5.4
-
3
8.3
19
SITTING HEIGHT TO
GROUND
SITTING EYE
HEIGHT TO GROUND
STEERING WHEEL
TO CHEST
CHEST CONTACT
POINT (1 - 9)
STEERING WHEEL
TO NASION
HEADREST TO TOP
OF EARS
BACK OF HEAD TO
HEADREST
In all cases there is a very close correlation between the position adopted in the
driver’s own vehicle and that adopted in the reference vehicle. This is exemplified by
the mean values for these dimensions which, despite the differing vehicle layout and
the ranges of adjustment, all match to within a few millimetres. This is shown in
Figures 34 and 35, which show the mean data sets for the own and reference vehicle
respectively.
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160
140
Range (cm or degree)
120
100
Small driver
Normal driver
80
60
40
20
0
Sitting
height to
ground
Sitting eye
height to
ground
Steering
wheel to
chest
Chest
contact
point (1 9)
Steering
wheel to
nasion
Elbow
angle
Hip angle Knee angle Foot angle Headrest
to top of
ears
Back of
head to
headrest
Figures 34: Own car driver seating measures
160
140
Range (cm or degree)
120
100
Small driver
Normal driver
80
60
40
20
0
Sitting
height to
ground
Sitting eye
height to
ground
Steering
wheel to
chest
Chest
contact
point (1 9)
Steering
wheel to
nasion
Elbow
angle
Hip angle Knee angle Foot angle Headrest
to top of
ears
Back of
head to
headrest
Figure 35: Reference car driver seating measures
Whilst it is clear, and to be expected, that there are noticeable differences between the
small drivers and their normal counterparts, the consistence between the two vehicles
suggests that drivers are very highly tuned to their preferred seating position and can
reproduce it accurately in different environments.
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This is a function of the kinaesthetic stimulus, which is related to comfort as well as
ease of use.
The implication from this observation is that it would be difficult to change this
positional selection through education or training since it is relatively highly
developed. It may be possible to educate new drivers, but those with an established
driving record have already determined what ‘feels right’.
The largest observed difference between the smaller and larger drivers was the elbow
angle, with larger drivers adopting a less acute angle. This supports the idea that
larger drivers seat further away from the steering wheel as a product of leg length.
However, mean distance to steering wheel from the chest did not differ by more than
10 cm over the four conditions, despite significant differences in driver stature.
Reach to controls
The reach to the controls of the vehicle was observed to be a fundamental variable in
selecting the driving position. This is demonstrated by the process by which driving
position is selected. Without exception, the first action of the driver is to slide the seat
forward or backward until the reach to the foot controls was acceptable. The back of
the seat was then adjusted before fine iteration took place including the height
adjustment, where fitted. The sensitivity to leg reach dimensions is shown in the data
in Tables 28 and 29. This gives the distances selected by drivers from the seat back
base join (referred to as the seat reference point or SRP) to the pedals. It can be seen
that the mean value for small drivers between their own and the reference vehicle
differs by less than 1.5 cm, whilst taller drivers only varied by up to 3 cm.
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Table 28: Reach to controls for small drivers
REACH TO CONTROLS
OWN
OWN
OWN
REF
REF
REF
(CM)
MIN
MEAN
MAX
MIN
MEAN
MAX
77
93.3
103
86
93.9
101
76
90.3
99
86
91.9
98
77
89.3
98
85
90.8
97
REAR SEAT BASE TO
ACCELERATOR
REAR SEAT BASE TO
BRAKE
REAR SEAT BASE TO
CLUTCH
Table 29: Reach to controls for normal drivers
REACH TO CONTROLS
OWN
OWN
OWN
REF
REF
REF
(CM)
MIN
MEAN
MAX
MIN
MEAN
MAX
92
103.0
111
97
102
108
88
99.0
108
10
96
106
87
97.6
104
94
98.9
105
REAR SEAT BASE TO
ACCELERATOR
REAR SEAT BASE TO
BRAKE
REAR SEAT BASE TO
CLUTCH
The mean data is presented in graphical form in Figure 36. The first pairing of
columns represents the drivers own car, the second pairing the reference car.
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105
100
Range (cm)
95
Rear seat base to accelerator
Rear seat base to brake
Rear seat base to clutch
90
85
80
Small driver own
Normal driver own
Small driver ref
Normal driver ref
Figure 36: Reach to controls for small and normal drivers
It can be seen that the smaller drivers are more consistent in their seating position
selection. This is likely to be a function of the necessity to adopt a more restrictive
position to control the vehicle, whilst taller drivers enjoy a greater degree of freedom.
In either case, if leg extension is the primary variable, the provision of a suitable range
of adjustment of either the seat or the pedals is vital to being able to adopt an
acceptable seating position.
Steering wheel location
The second most important factor observed in seat position selection was the
proximity of the steering wheel. However, for smaller drivers this could only largely
be controlled by adjustment of the seat back angle since the leg reach was restricted.
Larger drivers had more freedom to select a variety of seat base positions and
correlating this with appropriate seat back adjustment. The steering wheel location
data is given in Table 30 and 31.
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Table 30: Steering wheel location for small drivers
STEERING WHEEL
OWN
OWN
OWN
REF
LOCATION (CM)
MIN
MEAN MAX
MIN
SEAT BACK TO FURTHEST
POINT STEERING WHEEL
SEAT BACK TO MIDDLE
STEERING WHEEL
REF
REF
MEAN MAX
49
63.4
101
53
63.2
72
35
52.2
91
40
51.7
69
REF
REF
Table 31: Steering wheel location for normal drivers
STEERING WHEEL
OWN
OWN
OWN
REF
LOCATION (CM)
MIN
MEAN MAX
MIN
SEAT BACK TO FURTHEST
POINT STEERING WHEEL
SEAT BACK TO MIDDLE
STEERING WHEEL
MEAN MAX
68
73.5
82
68
75.3
83
55
61.2
72
56
61.8
69
This data is further presented in graphical form in Figure 37. This again shows a
remarkable degree of consistency between the driver in their own car and in a
reference vehicle – to within 5 mm for the critical seat back to steering wheel
middle. More variation is noted from the seat back to the furthest point of the
steering wheel, since the wheel angle and size differed between the two vehicles.
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80
70
60
Range (cm)
50
Seat back to furthest point steering wheel
Seat back to middle steering wheel
40
30
20
10
0
Small driver own
Normal driver own
Small driver ref
Normal driver ref
Figure 37: Steering wheel location for small and normal drivers
This data further reinforces the strength of the messages controlling seat position
for the individual. The two dimensions of leg reach and steering wheel proximity
are the most important positional cues almost to the point of exclusion of other
factors.
Control access
Once a suitable seating position has been selected, it is necessary to reach the
peripheral controls. As has been shown, the reach to the pedals and the proximity
of the steering wheel drive the seat set up, and reach to the controls is likely to be
a secondary function. This may result in dissatisfaction for knowledgeable users
or a compromise in safety for individuals who may just accept the configuration
offered (such as second users or naïve drivers). The data for the control access is
given in Table 32 and 33. It should be noted that the abbreviation HVAC is used
throughout this report which stands for ‘heating, ventilation and air conditioning
controls’.
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Table 32: Control access for small drivers
CONTROL ACCESS
OWN
OWN
OWN
REF
(CM)
MIN
MEAN MAX
MIN
REAR SEAT BASE TO GEAR
LEVER
REAR SEAT BASE TO
FURTHEST HVAC*
REF
REF
MEAN MAX
45
59.3
87
53
58.3
76
48
76.3
93
63
81.3
89
REF
REF
* Heating, ventilation and air conditioning controls
Table 33: Control access for normal drivers
CONTROL ACCESS
(CM)
REAR SEAT BASE TO GEAR
LEVER
REAR SEAT BASE TO
FURTHEST HVAC
OWN
OWN
OWN
REF
MIN
MEAN MAX
MIN
MEAN MAX
53
66.0
79
57
62.8
71
73
86.4
97
80
89.3
96
A graphical representation of the mean values is given in Figure 38, where the first
grouping illustrating the driver’s own car, the second the reference car.
100
90
80
70
Range (cm)
60
Rear seat base to gear lever
Rear seat base to furthest HVAC
50
40
30
20
10
0
Small driver own
Normal driver own
Small driver ref
Normal driver ref
Figure 38: Access to controls for small and normal drivers
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As is expected, there is somewhat more variation in these control reaches than for the
primary controls. This is mostly because of variation in the layout of the two
vehicles, as drivers accept more compromise in secondary control access as a function
of addressing primary seating position stimuli.
Reasons for adopting that position
The motivations for adopting the chosen posture may be attitudinal, which may be
altered through education, or may be functional as a result of body dimensions or
strength in which case they are less likely to be changed.
General posture
Participants were asked to record their ranking of the reach to the pedals, steering
wheel and gear lever along with the vision from the vehicle on a scale of 1 to 5, with 1
being the most important.
Table 34 shows the responses as a percentage of each of the populations of small and
drivers. The data is presented as a series of cumulative histograms in Figure 39
Table 34: General posture considerations for small drivers
RANKING (1 – 5)
PEDAL REACH
STEERING WHEEL
REACH
GEAR LEVER
REACH
VISION
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77 %
18 %
2%
3%
0%
28 %
25 %
44 %
3%
0%
13 %
6%
32 %
49 %
0%
46 %
25 %
11 %
18 %
0%
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180%
160%
140%
120%
100%
Vision
Gear lever reach
Steering wheel reach
Pedal reach
80%
60%
40%
20%
0%
Count 1
Count 2
Count 3
Count 4
Count 5
Figure 39: General posture for small drivers
Pedal reach was the variable which received the largest ranking as number 1 (77%),
scoring nearly double the next nearest variable, which was vision (46%). Gear lever
reach and steering wheel reach were ranked much less highly, accounting for only
13% and 28% of the 1st place ranking respectively.
The data for normal driver followed a somewhat different trend. Although pedal
reach was still regarded as the most important consideration (64%), the remaining first
place rankings was split equally between steering wheel reach and vision (22.5%
each). Gear lever reach was not ranked first by any individual. This data is presented
in Table 35 and Figure 40.
Table 35: General posture considerations for normal drivers
RANKING (1 – 5)
PEDAL REACH
STEERING WHEEL
REACH
GEAR LEVER
REACH
VISION
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64 %
27 %
9%
0%
0%
22.5 %
40.5 %
22.5 %
13.5 %
0%
0%
13.5 %
22.5 %
54 %
1%
22.5 %
22.5 %
45 %
9%
0%
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180%
160%
140%
120%
100%
Vision
Gear lever reach
Steering wheel reach
Pedal reach
80%
60%
40%
20%
0%
Count 1
Count 2
Count 3
Count 4
Count 5
Figure 40: General posture for normal drivers
The most important implication here is that all drivers find pedal reach a critical factor
in selecting a driving position, but small drivers are also much more constrained by
vision capabilities. This may suggest that small drivers would significantly benefit
from the ability to locate themselves in a car in a position which offers similar vision
to taller drivers. This might require a wider range of seat height adjustment, which
brings with it issues of reach to pedals and proximity of the steering wheel. However,
the pedal reach, steering wheel reach and vision variables dominate the selection of
seating positions for smaller and taller drivers.
General anthropometry
Unlike the position of the occupant in the vehicle and the location of the controls
around them, the anthropometry of the individual cannot be altered. The dimensions
of the body dictate the requirements of the vehicle to provide a comfortable and safe
seating position. In this respect, the specification for a satisfactory vehicle should be
relatively straightforward, since the anthropometry of the population of individuals is
relatively well understood and, whilst there are ethnicity differences, largely
unchanging. However, the variation on provision of seating adjustment between
manufacturers and their models suggests that even basic anthropometry features are
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being approached differently. Table 36 and 37 present basic anthropometric data for
the small and normal driver populations, and these are contrasted in Figure 41.
Table 36: General static anthropometry for small drivers
ANTHROPOMETRY (CM)
MIN
MEAN
MAX
STATURE
140
155.0
162
[(PERCENTILE]
[0.01]
[6.3]
[26.5]
UPPER LEG
43
51.7
57
LOWER LEG
29
40.7
51
SITTING HEIGHT
65
76.2
90
[PERCENTILE]
[0.01]
[0.2]
[60.5]
Table 37: General static anthropometry for normal drivers
ANTHROPOMETRY (CM)
MIN
MEAN
MAX
STATURE
161
175.0
193
[PERCENTILE]
[23.1]
[72.8]
[99.7]
UPPER LEG
47
53.9
63
LOWER LEG
42
48.3
55
SITTING HEIGHT
74
83.0
94
[PERCENTILE]
[0.03]
[12.0]
[85.4]
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200
180
160
140
Range (cm)
120
Small driver
Normal driver
100
80
60
40
20
0
Stature
Upper leg
Lower leg
Sitting height
Figure 41: General anthropometry for small and normal drivers
This reveals the relatively small range in the dimensions between the means of the
two populations. Accordingly, the range of adjustment necessary within the vehicle
to accommodate these individuals is not very great and should be achievable by
conventional technology without significant cost.
It is true that some individuals fall outside the normal design parameters of 5th to 95th
percentile (normally females for small dimensions, males for large ones) and there
may be some legitimacy in an argument saying that not all can be included. However,
the majority of the population can be accommodated with only a limited range of
adjustment provided it is centred around the appropriate point.
Adopted angles
The angles apparently adopted when selecting a seating position may, in fact, be the
result of more rigid dimensional requirements. Leg length overall, for instance, when
superimposed onto the reach to the foot controls, will dictate the angles that must be
adopted. However, those resultant angles must fall within recommended guidelines in
order to provide an adequate degree of control and comfort. Accordingly it can be
seen that provision of appropriate reaches and suitable ranges of adjustment will
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permit the selection of a greater variety of positions which will, in turn, accommodate
a greater range of individuals with higher level of satisfaction. Tables 38 and 39 show
the angles measured on the sample populations in their own and the reference
vehicles. Figure 42 makes this data more presentable and groups it into own vehicles
for the first pairing and reference vehicle for the second.
Table 38: Adopted angles for small drivers
ADOPTED ANGLE
OWN
OWN
OWN
REF
REF
REF
MIN
MEAN
MAX
MIN
MEAN
MAX
HIP ANGLE
90
112.8
150
80
111.1
150
KNEE ANGLE
95
120.2
150
80
121.6
155
FOOT ANGLE
80
103.5
130
70
103.8
130
Table 39: Adopted angles for normal drivers
ADOPTED ANGLE
OWN
OWN
OWN
REF
REF
REF
MIN
MEAN
MAX
MIN
MEAN
MAX
HIP ANGLE
100
113.6
140
105
115.9
140
KNEE ANGLE
100
125.9
140
115
126.8
145
FOOT ANGLE
85
100.5
120
95
104.1
115
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140
120
Range (degrees)
100
80
Hip angle
Knee angle
Foot angle
60
40
20
0
Small driver own
Normal driver own
Small driver ref
Normal driver ref
Figure 42: Adopted angles for small and normal drivers
In this figure it can be seen that hip angle is relatively constant across the populations,
as is foot angle. Knee angle shows the greatest variation although even that is not
large (6.6°). The consistency of each group between the two cars is again remarkable,
reflecting the precision with which of the seat position is selected.
Table 40 presents similar data for the elbow angle selected by drivers, again
illustrated in histogram form in Figure 43.
Table 40: Selected elbow angle
ELBOW ANGLES
OWN
OWN
OWN
REF
REF
REF
MIN
MEAN
MAX
MIN
MEAN
MAX
SMALL DRIVERS
80
121.8
180
85
123.6
180
NORMAL DRIVERS
110
143.4
180
130
149.3
180
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160
140
120
Range (degrees)
100
Small drivers
Normal drivers
80
60
40
20
0
Own car
Refrence car
Figure 43: Elbow angle for small and normal drivers
This also shows a high degree of consistency for each population between the
vehicles, but a much larger variation between the populations themselves (27.5°).
Smaller drivers are typically adopting a more acute angle. This may suggest that their
arms are longer in proportion to their legs or that they prefer a more upright posture.
Females generally have shorter arms and torsos than males of similar stature and,
since the majority of small drivers are women, this may amplify possible problems.
In this evaluation it appears that smaller drivers, typically women, are significantly
compromised since their shorter arms should result in more relaxed angles. In fact
they are nearer the wheel through shortness of reach and through the adoption of more
acute angles.
This may not be solely due to anthropometric restriction, but may also represent
attitudinal effects, such as feelings of control or the need to generate more mechanical
leverage so as to provide adequate control.
The shorter arms of smaller drivers and women also affect the reach to the controls of
the vehicle, and may require that a more forward seating position is adopted or that a
more upright seat back angle is established. Tables 41 and 42 provide the data on the
reach to the controls for the smaller and normal drivers in their own and the reference
vehicle.
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Table 41: Seat to major control distances for small drivers
CONTROL REACH
OWN
OWN
OWN
REF
REF
REF
(CM)
MIN
MEAN
MAX
MIN
MEAN
MAX
49
63.4
101
53
63.2
72
35
52.2
91
40
51.7
69
45
59.3
87
53
58.3
76
48
76.3
93
63
81.3
89
SEAT BACK TO
FURTHEST POINT
STEERING WHEEL
SEAT BACK TO
MIDDLE STEERING
WHEEL
REAR SEAT BASE TO
GEAR LEVER
REAR SEAT BASE TO
FURTHEST HVAC
Table 42: Seat to major control distances for normal drivers
CONTROL REACH
OWN
OWN
OWN
REF
REF
REF
(CM)
MIN
MEAN
MAX
MIN
MEAN
MAX
68
73.5
82
68
75.3
83
55
61.2
72
56
61.8
69
53
66.
79
57
62.8
71
73
86.4
97
80
89.3
96
SEAT BACK TO
FURTHEST POINT
STEERING WHEEL
SEAT BACK TO
MIDDLE STEERING
WHEEL
REAR SEAT BASE
TO GEAR LEVER
REAR SEAT BASE
TO FURTHEST
HVAC
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This mean data sets for each of these are extracted and presented as a histogram in
Figure 44
100
90
80
70
Range (cm)
60
Small driver own
Small driver ref
Normal driver own
Normal driver ref
50
40
30
20
10
0
Seat back to furthest point
steering wheel
Seat back to middle steering
wheel
Rear seat base to gear lever
Rear seat base to furthest
HVAC
Figure 44: Seat to major control distances for small and normal drivers
Here it can be seen that the reach from the seat back to the steering wheel and gear
lever remain almost constant between the driver’s own and the reference vehicle. The
reach to the furthest HVAC is more varied due to the different location in the two
vehicles.
This is somewhat surprising since, given that there are differences in the design of the
two vehicles, the relative reaches would be different. However, given the limited
variation in elbow angle between the postures in two vehicles it would appear that the
drivers may be using the fore aft adjustment to fine tune this reach.
Access to primary and secondary controls
Consideration was given to the accessibility of all the primary and secondary vehicle
controls, and this data is presented in Table 43 for small drivers and Table 44 for the
normal driving sample population.
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Table 43: Reach to controls for small drivers
CONTROL REACH
OWN
OWN
OWN
REF
REF
REF
(CM)
MIN
MEAN
MAX
MIN
MEAN
MAX
77
93.3
103
86
93.9
101
76
90.3
99
86
91.9
98
77
89.3
98
85
90.8
97
0
10.6
16
9
9.0
9
BRAKE HEIGHT
8
13.3
18
10
10.0
10
CLUTCH HEIGHT
9
14.3
18
12
12.0
12
49
63.4
101
53
63.2
72
35
52.2
91
40
51.7
69
59
69.8
91
52
70.1
78
45
59.3
87
53
58.3
76
48
76.3
93
63
81.7
89
REAR SEAT BASE
TO ACCELERATOR
REAR SEAT BASE
TO BRAKE
REAR SEAT BASE
TO CLUTCH
ACCELERATOR
HEIGHT
SEAT BACK TO
FURTHEST POINT
STEERING WHEEL
SEAT BACK TO
MIDDLE STEERING
WHEEL
CLUTCH TO
MIDDLE STEERING
WHEEL
REAR SEAT BASE
TO GEAR LEVER
REAR SEAT BASE
TO FURTHEST
HVAC
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Table 44: Reach to controls for normal drivers
CONTROL REACH
OWN
OWN
OWN
REF
REF
REF
(CM)
MIN
MEAN
MAX
MIN
MEAN
MAX
92
103.0
111
97
102
108
88
99.0
108
10
96
106
87
97.6
104
94
98.9
105
0
10.3
16
9
9
9
BRAKE HEIGHT
9
13.3
17
10
10
10
CLUTCH HEIGHT
7
13.8
18
12
12
12
68
73.5
82
68
75.3
83
55
61.2
72
56
61.8
69
67
72.7
82
64
73
77
53
66.0
79
57
62.8
71
73
86.4
97
80
89.3
96
REAR SEAT BASE
TO ACCELERATOR
REAR SEAT BASE
TO BRAKE
REAR SEAT BASE
TO CLUTCH
ACCELERATOR
HEIGHT
SEAT BACK TO
FURTHEST POINT
STEERING WHEEL
SEAT BACK TO
MIDDLE STEERING
WHEEL
CLUTCH TO
MIDDLE STEERING
WHEEL
REAR SEAT BASE
TO GEAR LEVER
REAR SEAT BASE
TO FURTHEST
HVAC
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When the mean values for these dimensions are extracted they can be directly
compared, and this is shown in Figure 45. Note that the height of the foot controls has
been omitted to permit a suitable scale to be used.
120
100
Range (cm)
80
Small driver own
Small driver ref
60
Normal driver own
Normal driver ref
40
20
0
Rear seat base Rear seat base Rear seat base Seat back to
Seat back to
Clutch to
Rear seat base Rear seat base
to accelerator
to brake
to clutch
furthest point middle steering middle steering to gear lever
to furthest
steering wheel
wheel
wheel
HVAC
Figure 45: Reach to major controls for small and normal drivers
This shows tight pairings between the small drivers in their own and the reference
vehicles. The taller drivers show more variability, again illustrating that they have the
capacity to choose from a range of seating positions whilst small drivers are more
restricted by their body dimensions. Generally however, there is a relatively
consistent variance between the small driver and the normal population. This suggests
that the smaller drivers can be accommodated by the provision of a suitable range of
adjustment, which would permit them to position themselves closer to the three
dimensional location of the taller drivers in the vehicle.
Quality of drivers view of the road
Vision from the vehicle was cited as the second most important criteria in selecting a
seating position, after reach to the pedals. Accordingly, the restrictions to vision for
smaller drivers needed to be quantified.
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Table 46 gives the distance that driver could see a road level point in front of the
vehicle. It was hoped to provide similar data for rear vision, but the variation in
coping strategy (left/right shoulder, sitting up, leaning across seat back etc.) and
vehicle design did not permit the collection of meaningful data. Forward vision,
however, was more consistent through control of the seated posture and the
conventionality of design.
Table 46: Forward vision for drivers to a point at road surface height
FORWARD VISION
OWN
OWN
OWN
REF
REF
REF
(CM)
MIN
MEAN
MAX
MIN
MEAN
MAX
SMALL DRIVERS
420
646.0
1269
498
642.12
1187
NORMAL DRIVERS
479
594
702
505
585
689
This data is made more meaningful by presentation in histogram form in Figure 46.
700
600
Range (cm)
500
400
small drivers
Normal drivers
300
200
100
0
Own car
Reference car
Figure 46: Forward vision for small and normal drivers
It can readily be seen that smaller drivers suffer compromised vision from their
reduced stature. The visual field generated by the vehicle dashboard and scuttle
means that small drivers could see less of the road surface by between 50 and 140 cm
dependant on the vehicle. Whilst this may not present difficulty during normal driving
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when the vehicle is moving at speed (it would not impact on stopping distances, for
instance) it may cause problems during tighter manoeuvres such as parking or slow
speed turning. Given the reduced strength of females compared to males, this may
also mean that a further compromised posture is required if the vehicle’s controls are
not light in operation.
It would appear rational that a greater range of control adjustment would permit the
smaller driver to sit in a more elevated position and thus enjoy better vision without
restricting access to, and use of, the controls.
Knowledge of adjustment
In order to appraise the knowledge of the adjustment features available to the driver
and the ease of their use a simple ranking device was used. Each feature was rated
between 1 and 5, with 1 equating to a lack of knowledge or a difficult control to use.
The mean scores generated are presented in Table 47 and also shown in Figure 47.
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Table 47: Small and normal driver seat & steering wheel adjustment knowledge
RANKING
(1 – 5)
SMALL DRIVERS
NORMAL DRIVERS
OWN MEAN REF MEAN OWN MEAN REF MEAN
OVERALL POSITION
3.9
3.7
4.2
3.6
4.9
4.7
5
5.0
4.6
4.5
4.5
4.5
4.1
3.1
4.6
4.2
4.1
4.0
3.9
4.2
4.7
4.3
4.8
4.7
SEAT BACK EASE
4.4
4.5
4.5
2.9
SEAT BASE KNOWLEDGE
3.6
-
4.5
-
SEAT BASE EASE
4.2
-
4.5
-
2.9
2.9
4.2
3.9
3.7
3.7
4.3
3.6
(1 - 5)
SEAT FORE/AFT
KNOWLEDGE
SEAT FORE/AFT EASE
SEAT HEIGHT
KNOWLEDGE
SEAT HEIGHT EASE
SEAT BACK
KNOWLEDGE
SW ADJUST
KNOWLEDGE
SW ADJUST EASE
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6
5
Ranking (1 - 5)
4
Small driver own
Small driver ref
Normal driver own
Normal driver ref
3
2
1
as
ad
ju
st
e
dg
le
st
k
ju
ad
SW
no
w
e
tb
as
SW
Se
a
e
e
e
ea
s
ge
w
Se
a
tb
as
e
tb
Se
a
ac
k
tb
kn
o
ac
k
le
ow
kn
ei
th
le
d
ea
se
dg
e
as
e
gh
w
Se
a
tk
no
gh
th
ei
Se
a
Se
a
as
ft
e
or
e/
a
Se
at
f
te
le
dg
e
e
e
dg
le
no
w
Se
a
tf
or
O
e/
af
tk
ve
ra
l
lp
os
iti
on
0
Figure 47: Knowledge and ease of use of seat adjustment for small and normal
drivers
Not unsurprisingly, drivers were relatively familiar with their own vehicle’s
adjustment provision, although ease of use generally received a slightly lower score.
A noticeable exception was the steering wheel adjustment for the smaller driver
population, which was not well understood or operated. This may be an area which
could be valuably explored by manufacturers since smaller divers may have the most
to gain from use of this adjustment facility.
The normal driver population were more knowledgeable about the adjustment
provision, though this may be a function of the larger percentage of males in this
group and their traditional increased exposure to vehicle products. Their ease of use
scores were generally similar to the smaller drivers.
Perceived adequacy of position
A similar ranking was used to estimate the driver’s satisfaction with the adequacy of
the seat position they had chosen. A score of 1 indicated that it was considered ‘very
poor’ whilst 5 equated to ‘very good’. The means scores are given in Table 48.
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Table 48: Driver perceived adequacy of seat position
OVERALL POSITION
OWN
REF
(1 – 5)
MEAN
MEAN
SMALL DRIVERS
3.9
3.7
NORMAL DRIVERS
4.3
3.6
It can be seen that smaller drivers were more dissatisfied with their own vehicle
seating position than the normal drivers. However, the scores for the reference
vehicle were very similar. This suggests that smaller drivers are not able to obtain a
position in their vehicle with which they are happy, despite familiarity with the
adjustment provided. The posture available in the reference vehicle may either be less
popular overall, or it may take longer exposure to reach a point of satisfaction.
Importance of driving position in car purchase
Given that driving position is critical to driver comfort, performance and safety, the
importance of driving position in the car purchase decision was evaluated. Drivers
were asked if the driving position was a significant factor in the choice of car to
purchase and, if so, how important on a scale of 1 to 10 where 10 was ‘very
important’. The results are shown in Table 49.
Table 49: Driving position importance in car purchase
IS DRIVING POSITION SIGNIFICANT (1 – 10)
MEAN
‘10’ SCORE
SMALL DRIVER - HOW IMPORTANT ?
8.8
37%
NORMAL DRIVER - HOW IMPORTANT ?
8.1
14%
Small drivers rated seating position as somewhat more important that normal drivers.
However, a considerable number of smaller drivers considered it very important,
nearly three time as many as normal drivers. Small drivers, it appears, are prepared to
place a higher priority on this variable when it comes to spending money, which may
be of interest to retailers and manufacturers.
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Drivers were asked what other factors influenced their buying decision, and the varied
responses are presented in Table 50. It was not possible to rank these given the
diversity of the variables, but the breadth of influences in the buying decision is
clearly apparent.
Table 50: Other factors cited as important in car choice
Comfort
Automatic
Adjustability
Price
Make/model
Safety
Central locking
Power steering
Visibility
Style
Colour
Interior design
Economy
Size
Reliability
Ease of use of controls
Manoeuvrability
Engine size
Maintenance costs
Insurance costs
History
Boot space
4x4 capability
Handling
Number of doors
Steering wheel size
Brakes
Manual
Diesel
Quietness (engine)
Awareness of hazards of close seating position
Some of the most pertinent data collected relates to the awareness of drivers to the
hazards of sitting close to the steering wheel in a car fitted with an airbag. This
information was collected in a direct and straightforward form, by asking if the
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benefit of an airbag was dependent on the seat position. The responses are shown in
Table 51.
Table 51: Perceived dependence of airbag performance on seat position
BENEFIT DEPENDENT ON
YES
NO
SMALL DRIVERS
71 %
23 %
NORMAL DRIVERS
91 %
9%
SEAT POSITION ?
The vast majority of drivers did believe that the benefit of airbags was dependent on
seat position, although less than three quarters of small drivers were aware of this
whilst over 90 % of normal drivers knew this to be the case. This again probably
represents the cultural aspects of the female predominance in the small driver
population. However, this level of awareness suggests those who have most to gain
from an airbag are also those that have the highest level of ignorance regarding seat
position.
In order to further explore this issue, the participants who responded positively with
regard to the importance of seat position were asked where it was best and worst to
sit. Options for reply were restricted to ‘far’, ‘close’, ‘centre’ and ‘other’.
The responses are presented as percentages of the whole of each population in Table
52 for smaller drivers and for the normal population.
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Table 52: Perceived best location to sit responses
COUNT
FAR
CLOSE
CENTRE
OTHER
NOT
KNOWN
WHERE
BEST TO
SMALL
SIT
DRIVERS
WHERE
WORST
59 %
3%
1%
6%
31 %
8%
0%
1%
58 %
33 %
86 %
0
14 %
0
0
0
0
14 %
86 %
0
TO SIT
WHERE
BEST TO
NORMAL
SIT
DRIVERS
WHERE
WORST
TO SIT
Only just over half of all the small drivers felt that sitting far away from the steering
wheel was the best location, with 6% believing sitting close to the wheel was good.
However, for the normal population 86% knew that sitting far from the steering wheel
was best whilst none felt that sitting close was recommended. The 14 % of normal
drivers recording a response of ‘other’ generally replied with other postural features,
such as ‘sitting upright’. This data is presented in graphical from in Figures 48 and
49.
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100%
90%
80%
70%
60%
Small drivers best
Normal drivers best
50%
40%
30%
20%
10%
0%
far
close
centre
other
Figure 48: Small and normal driver opinion as to where is best to sit
100%
90%
80%
70%
60%
Small drivers worst
Normal drivers worst
50%
40%
30%
20%
10%
0%
far
close
centre
other
Figure 49: Small and normal driver opinion as to where is worst to sit
This data is worrying since it suggests that smaller drivers, for whom driving position
choice is more limited and who choose or need to sit closer to the steering wheel are
also the individuals who are least aware of the dangers of doing so.
Clearly this implies that there is a hole in the knowledge base that needs to be
addressed even if no other interventions are exploited. Unfortunately, these
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individuals at risk may well be those with the least interest in vehicle technology and
hence this may present a difficult educational challenge.
As part of a further investigation, comparison was made of the distances that drivers
chose to sit from the steering wheel to the distance they believed was best. The
steering wheel to chest measurement was taken directly in the vehicle, and the ‘best
practice’ stated distance was quantified by asking drivers to indicate with their hand
how far the steering wheel should be from the chest. The results are enlightening and
are presented in Table 53.
Table 53: Comparison of stated proximity to steering wheel with observed
practice
STEERING WHEEL TO CHEST
OBSERVED
OBSERVED
OBSERVED
DISTANCE (CM)
OWN MIN
OWN MEAN
OWN MAX
23 (20)
32.6 (35.9)
49 (48)
20
36.6
50
29 (34)
40.6 (41.6)
51 (48)
25
37.7
47
OBSERVED SMALL
DRIVERS OWN CAR
(REFERENCE )
SMALL DRIVERS (STATED)
OBSERVED NORMAL
DRIVERS OWN CAR
(REFERENCE)
NORMAL DRIVERS (STATED)
The mean distance for small driver’s chest to steering wheel in their own car was 32.6
cm, and that for the normal drivers 40.6 cm. This 8 cm difference appears very small
compared with the differences in gross stature. However, the perceived ‘best
practice’ location was almost the same for both groups at approximately 37 cm.
In the reference car, both populations sat further from the steering wheel, although
this may be a function of the vehicle layout rather than the preference of the driver.
However, even the smallest mean distance (32.6 cm – small driver, own car) is
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significantly greater than the 25.4 cm recommendation currently being made by
NHTSA.
Some individuals did choose to sit considerably closer to the steering wheel, with one
individual only 20 cm away, and these may benefit most from changes to education.
Figure 50 illustrates the differences between the populations. It is interesting to
observe that whilst both populations were similarly minded regarding the distance
they should be from the steering wheel, they were equally poor at locating themselves
at this distance, or were not motivated to do so. Notably, the small drivers were
nearer than they believed they needed to be, whilst taller drivers were further away.
45
40
35
Range (cm)
30
25
Small driver
Normal driver
20
15
10
5
0
Stated
Observed own
Observed ref
Figure 50: Stated and observed wheel proximity for small and normal drivers
Alternative driving positions
In order to explore practical interventions that may be applied, drivers were asked to
adopt an alternative posture which effectively placed them as far as practical away
from the steering wheel and other controls. This was standardised as much as
possible by starting with the seat fully rearward and moving it forward until the
accelerator could just be fully depressed. The seat back angle was the inclined the
minimum necessary to exert control over the vehicle. The drivers attitude to this
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posture was recorded on a scale of 1 to 5, where 1 equated to ‘very unhappy’. The
data collected are presented in Table 54 and Figure 51.
Table 54: Perceived acceptability of alternative seating position
RANK (1-5)
1
2
3
4
5
SMALL DRIVERS
35 %
36 %
15 %
11 %
3%
OWN (REF)
(29 %)
(30 %)
(22 %)
(11 %)
(8 %)
NORMAL DRIVERS
9%
41 %
23 %
9%
18 %
OWN (REF)
(9 %)
(36 %)
(27 %)
(18 %)
(9 %)
160%
140%
120%
100%
Normal driver ref
Normal driver own
Small driver ref
Small driver own
80%
60%
40%
20%
0%
1
2
3
4
5
Figure 51: Perceived acceptability of alternative posture for small and normal
drivers
It can be seen that this position was not popular, with a typical ranking for both
populations in both vehicles of 2 (‘unhappy’). This presents problems for any
education program trying to change the seating position in this fashion, since
individuals will be far more motivated by their immediate feelings than the remote
possibility of an accident scenario. The dissatisfaction reflected feelings of lack of
control, poor vision and also discomfort and so may bring with it its own inherent
safety problems.
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The key dimensions of the postures adopted in this alternative position are given in
Table 55 for smaller drivers and Table 56 for the normal population. The populations
are combined in the presentation in Figure 52.
Table 55: Alternative seating posture for small drivers
ALTERNATIVE
OWN
OWN
OWN
REF
REF
REF
POSTURE
MIN
MEAN
MAX
MIN
MEAN
MAX
ELBOW ANGLE
80
138.7
180
95
144.7
180
HIP ANGLE
80
117.9
150
80
120.5
150
KNEE ANGLE
110
128.8
150
100
126.3
160
FOOT ANGLE
85
111.2
150
85
110.0
170
23
36.8
50
25
36.4
48
31
43.4
54
34
42.1
54
STEERING WHEEL
TO CHEST (CM)
STEERING WHEEL
TO NASION (CM)
Table 56: Alternative seating posture for normal drivers
ALTERNATIVE
OWN
OWN
OWN
REF
REF
REF
POSTURE
MIN
MEAN
MAX
MIN
MEAN
MAX
ELBOW ANGLE
85
151.1
180
140
160.0
180
HIP ANGLE
105
117.7
140
110
119.1
140
KNEE ANGLE
110
132.0
155
115
131.8
150
FOOT ANGLE
10
100.7
125
100
108.2
130
36
44.6
54
36
45.3
52
43
50.9
59
39
50.2
58
STEERING WHEEL
TO CHEST (CM)
STEERING WHEEL
TO NASION (CM)
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180
160
140
Range (cm or degrees)
120
Small driver own
Small driver ref
Normal driver own
Normal driver ref
100
80
60
40
20
0
Elbow angle
Hip angle
Knee angle
Foot angle
Steering wheel to
chest (cm)
Steering wheel to
nasion (cm)
Figure 52: Alternative seating postures for small and normal drivers
The most significant figure is the revised distance to the steering wheel for the smaller
drivers. In their preferred seating position, the mean distance chest to steering wheel
was 32.6 cm in their own car and 35.9 cm in the reference car. This is increased to
36.8 cm and 36.4 cm respectively in the adjusted position. This indicates that not
only is there very limited capacity to increase this critical distance through the current
seat adjustment provision, but also that in the current form accessing such safety
benefits results in a high degree of driver dissatisfaction with the overall position.
As a final component of this data appraisal, a correlation was made of the distance
between the steering wheel and chest and three basic anthropometric dimensions. The
dimensions chosen were stature, arm length, leg length and sitting height. These
correlations were made for each individual in the two populations, and the results are
shown in Figure 53 for small drivers and Figure 54 in the normal driver population.
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180
160
140
Value (cm)
120
Stature
Arm
Leg
Sitting height
Linear (Arm)
Linear (Sitting height)
Linear (Leg)
Linear (Stature)
100
80
60
40
20
0
0
10
20
30
40
50
60
Steering wheel to chest (cm)
Figure 53: Small driver steering wheel to dimensions correlation
250
200
Stature
Arm
Leg
Sitting height
Linear (Arm)
Linear (Sitting height)
Linear (Leg)
Linear (Stature)
Variable (cm)
150
100
50
0
0
10
20
30
40
50
60
Steering wheel to chest (cm)
Figure 54: Normal driver steering wheel to dimensions correlation
For the smaller drivers, all four correlations are close to linear. This suggests that for
this dimensionally more restricted population, the relatively small changes in sitting
height, leg or arm length have little influence on the distance from the steering wheel
that they choose to sit. Overall stature may be somewhat more useful in indicating the
level of risk exposed. However, for the more diverse normal population, a more
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dynamic correlation exists, with the larger dimensions all corresponding to increased
chest to steering wheel distances. It may be surmised, therefore, that the real world
smaller driver population may benefit from interventions which artificially address
any, or all, of these relationships.
4.4.4.
Conclusions
From this evaluation, the following key conclusions are drawn:
•
Small drivers sit with their chests closer to the steering wheel than normal
drivers, but typically only about 6 - 8 cm.
•
Small drivers are less aware of the safety consequences of sitting too close
to the steering wheel
•
Some small drivers believe sitting closer to the steering wheel is better for
airbag performance
•
Small drivers are unable to sit further away from the steering wheel
primarily because their leg length dictates the proximity of the SRP to the
steering wheel and the seat back angle can only provide limited
compensation
•
Vision and reach to the pedals are the critical factors in small driver
seating position choice
•
Access to the secondary controls is subordinate to the need to reach the
pedals and see from the vehicle for small drivers
•
Small drivers are less knowledgeable about steering wheel adjustment and
find it harder to operate than the normal population
•
Seating posture is learned and strongly maintained in established and new
vehicles with a high degree of precision
•
Gaining changes in posture is unlikely through education or information
•
An alternative seating position further from the steering wheel is
unpopular and not effective at increasing the distance very much
•
Small driver vision is compromised for low speed manoeuvres
•
Seat position is considered important for small drivers, and provides a
significant part of the car purchase procedure
•
Small drivers are not as happy with their driving position as normal drivers
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4.5.
4.5.1.
Sept 2003
Consideration of counter measures and remedial actions.
Aim
The aim of this activity is to investigate counter measures and remedial actions which
may assist small drivers in adopting a more rearward seating position in relation to the
steering wheel. The following methods by which this may be achieved were
considered:
•
Seat adjustability,
•
Adjustable pedals and pedal extenders,
•
Adjustable steering wheels,
•
Advanced airbag designs,
•
Improved driver education.
In addition, information to form the basis of a cost-benefit analysis was gathered
where it was available.
4.5.2.
Methodology
A literature/research review of potential solutions to sitting close to the steering wheel
was undertaken. An international review of information via the internet was also
undertaken.
4.5.3.
Findings
Seat adjustability
Fore-aft adjustability: McFadden et al (2000) found that the height of the driver was
the most important determinant of driver distance from the steering wheel. On
average, for every 10cm increase in height, the driver sat at least 3cm further away
from the steering wheel. This suggests that a certain amount of seat adjustment is
required to accommodate a range of drivers. Whilst most, if not all cars, now provide
fore-aft seat adjustment, the amount of that adjustment and its proximity to the
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dashboard and controls are variable. Each driver should therefore try a car before
opting to purchase. Refer to Figure 55.
(a)
(b)
Fore-aft adjustment of the drivers seat, which is now fitted as standard on most models, permits
drivers to sit further back from the steering wheel and dashboard. (Note the decreased proximity
of the drivers face from the steering wheel and the more open angle at the elbow of figure (b)
compared to figure (a)
Figure 55: Fore-aft seat adjustability
Height adjustment: Height adjustment is not such a common feature – generally
being available on medium to high specification models. There are a number of
methods by which the seat can be adjusted by height, some of which are better in
terms of posture and ease of adjusting. The amount by which a seat varies in height is
also variable, some of the more generous being up to 50mm. Again the driver should
try out a car to determine if it suits them.
Benefit: Such adjustability makes driving vehicles accessible to more of the
population. It also improves driving posture and so can assist in reducing fatigue,
discomfort and health problems associated with driving. However such benefits and
the number of drivers involved makes these benefits difficult to quantify.
Cost: Fore-aft adjustability is available, as standard on the majority of vehicles and so
presents no additional cost to purchase price.
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Pedals
Whilst seat travel has enabled more drivers to sit sufficiently close to the use the
pedals, there are still some instances of drivers not being able to reach or operate the
pedals or do so comfortably. The traditional solution to this has been the use of pedal
extenders that fit onto the existing pedals raising their surfaces towards the driver. A
newer measure which has recently become available on some models of car is the
adjustable pedal system. Research in the USA found that 40% of short women
(5’2½”) sat closer than 10” in large and mid-size cars compared to 27% in small cars.
It was suggested that this may be because the steering wheel and accelerator pedal are
approximately 2” further apart in large cars than small ones.
Pedal extenders: Pedal extenders are relatively cheap and easy to fit. They vary in
the additional distance they are able to offer to the driver from 2” to up to 12”. Pedal
Pals, a brand of UK pedal extenders, state that they are approved by MAVIS at the
Department for Transport. The disadvantages are that pedals extenders can take some
time to get used to since they are heavier and bulkier than conventional pedals. Also
they are less adaptable to other drivers of the vehicle who do not need to use them.
Figure 56: Pedal extenders
Pedal adjusters: Pedal adjusters were first patented in the 1950s and incorporated in
larger General Motors vehicles some two decades later. Due to poor market uptake
they were phased out but have recently become more popular being re-introduced in
the 1990s in electronic form. They can position the pedals up to three inches nearer to
the driver, moving them horizontally and vertically, and are controlled by buttons next
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to the steering wheel. Since 1999 when they were first introduced to some Ford
models they have become that companies best-selling optional feature. They are
available as a package option or a stand-alone product. Some forms of this product
can be programmed to memorise the preferred positions for two drivers.
Figure 57: Schematic showing integral nature of pedal adjusters to the vehicle
design
Benefit: Such adjustability makes driving vehicles accessible to more of the
population. It also improves driving posture and so can assist in reducing fatigue,
discomfort and health problems associated with driving. However such benefits and
the number of drivers involved make these benefits difficult to quantify. The Ford
Motor Company is specifically careful to promote their pedals as comfort, opposed to
safety, features. In the US, it has been noted that whilst NHSTA is aware of their
availability for use by small drivers, their implications in terms of ease and safety of
use have not been analysed.
Costs: Pedal extenders cost $40.00 (up to $95.00 if they need to be custom made).
Pedal adjusters are standard on some vehicles and optional on others. Where they are
available as options, this is the region of $120.00.
Steering wheel
Once the seat has been adjusted forwards or backwards to comfortably reach the
pedals it is necessary to be able to adjust the reach to the steering wheel to optimise
the angle of the arms. For comfort, it is generally recommended that the distance
between the driver and the steering wheel is great enough to drive with just a slight
bend at the elbows.
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A recent development which assists this is the introduction of adjustable steering
columns that are now fitted as standard on some models of car. There are different
types of steering wheel adjustment - on some cars the steering wheel rotates up or
down about an axis just under the dashboard through a set number of positions, in
others the entire column shifts up or down and can be set exactly where required.
Other cars allow the steering wheel to move towards or away from the driver, and a
rare few allow both rake and reach adjustment. On a few exclusive models the
steering wheel electrically rises out of the way automatically when the engine is
switched off in order to allow easier entry/egress.
Figure 58: Diagram illustrating steering wheel adjustment
Delphi who manufacture several versions of adjustable steering wheels have a 10
degree adjusting arc and 50mm telescopic travel and sell their products on the grounds
of improved comfort rather than offering an additional safety benefit.
Benefit: Such adjustability improves driving posture and so can assist in reducing
fatigue, discomfort and health problems associated with driving. However such
benefits and the number of drivers involved makes these benefits difficult to quantify.
Cost: Steering wheel adjustment is available as standard on many vehicles and so
presents no additional cost to purchase price.
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Airbag design
The purpose of an airbag is to inflate immediately after a severe crash is initiated and
act as an energy-absorbing cushion protecting the driver from impact with hard
vehicle interiors. However there are instances in which the airbag can actually cause
injury to drivers – unbelted drivers, drivers who are out-of-position and drivers who
are sitting close to the airbag i.e. are at less than 10” from the steering wheel, are at
greatest risk of this. In the US, small drivers are considered to be at greater risk due
to their close seating proximity.
Figure 59: Airbag use
Deactivation switches: It is possible to install switches that can turn off the airbag
thereby preventing its deployment and eliminating the risks posed to the at-risk
drivers. However such action is considered to be a last resort since the considerable
potential safety benefits of the airbag are negated whilst the risks from the deploying
airbag are replaced with risks of contact by the driver with the steering wheel or
dashboard. The advice given in the US is to use seat-belts and sit back, using pedal
extenders if necessary before considering the use of an on-off switch.
Figure 60: Deactivation switch
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Airbag design:
Reduced energy airbags – Cars produced since 1998 have less powerful inflators and
so reduce the risks from airbag injuries. (Benefits obtained by this method are less
applicable to the UK since airbags used in this country are less powerful than those of
the US. This is due to the greater use of seat-belts by the UK population which
restrain the driver and so require less energy-absorption by the airbag).
Dual thresholds, two-stage inflators - Advanced airbag designs aim to tailor their
deployment to the specific conditions of the crash by considering exactly when to
deploy and how much force to use in the deployment. Dual threshold airbags deploy
at greater thresholds for belted drivers whilst two-stage inflators vary the force of the
airbag according to the type of crash. These advanced airbags are available on
Mercedes, BMW, Volvo S80s and Acura RLs.
Occupant sensing systems – These advanced airbags tailor their deployment
characteristics according to the weight and position of the occupant. These are
particularly useful for the front passenger seat in which small children and infant
carriers might be placed. The technologies used in these airbags utilise infra-red,
microwave or other detectors and may disengage the airbag if an occupant is too
close. The Ford Taurus has airbags of this type.
Benefit: Current thinking is that the safety benefits offered by airbags outweigh their
disbenefits. Data from the US indicates that driver airbags reduce deaths by about
14% in all crashes.
Cost: In terms of potential safety disbenefits, US data indicates that between 1990
and Feb 2002, 68 drivers were killed by airbags inflating in low severity crashes. Of
these 44 were believed to have been unbelted and of those who were belted the
majority were thought to be inappropriately belted or out-of-position. In terms of
price, airbags are available as standard on many models of vehicles and so presents no
additional cost to purchase price.
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Driver education
Information concerning the safety benefits and disbenefits of airbags is available on a
number of websites. In conjunction with general information pertaining to airbags,
the National Highway Transport Safety Administration (NHTSA) and the Insurance
Institute for Highway Safety provide specific advice to help drivers adopt a safer
driving position. Refer to Appendix 3 and Appendix 4.
The advice from various websites indicates that drivers should:
•
Use a lap and diagonal seat-belt,
•
Ensure they are sitting back in their seat, not leaning forward,
•
Move the seat rearwards as far as possible yet still achieving comfortable
use of the pedals,
•
If the driver is still closer than 10” (measured from the centre of the
steering wheel to the centre of the breastbone), then they should recline the
seat back,
•
If the driver has difficulty seeing the road, they should higher their seating
position,
•
If the steering wheel is adjustable, it should be tilted down to point the
airbag to the chest opposed to the head or neck.
•
The driver should hold the steering wheel from the sides so that their arms
are not between the driver and air bag thereby reducing the risk of arm and
hand injuries.
Figure 61: Excerpt from the NHSTA driver education document regarding
adopting a safer driving posture
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Benefit: The advantage of this approach is that it:
•
Alerts drivers to issues which they may not have been aware of previously,
•
Educates drivers in the safety benefits/disbenefits of airbags thereby
allowing them to have informed opinions,
•
Assists drivers in determining which approach to adopting a safer driving
position best suits them,
•
Provides a potential no-cost solution to drivers if through seat adjustment a
safer driving position can be obtained.
Cost: Generally low cost. (Paper-based distribution may be more wide-reaching than
web-based distribution, but the latter can be more readily amended).
4.5.4.
Conclusions
The investigation of remedial measures and counter-actions indicates two main means
for reducing the risks from airbags.
Remove the source of the risk, that is, address the design of the airbag such that less
injuries result from its use. This approach is being realised but further development is
required to maximise these benefits and time will also be needed to allow these
benefits trickle down to all vehicle models.
Remove the driver from the risk. Most of the measures discussed above take this
approach and aim to increase the distance between the driver and the airbag. Most of
these measures are currently available for implementation but at varying costs.
The way forward may therefore be to provide guidance as to how drivers may
optimise their safety by increasing their distance from the airbag that should be
reviewed when subsequent generations of advanced airbag designs are introduced.
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5.0
Finite Element Modelling
5.1.
Model set-up
5.1.1. Dummy
A 5th percentile female dummy model was chosen to represent the characteristics of a
small driver. The 5th percentile dummy model had been used extensively in previous
research projects and had shown to be a reliable representation of a small female
driver. Prior to the commencement of the simulations an initial review to ensure that
all necessary output could be obtained and calculated from the model was conducted.
The dummy’s joints were adjusted to position the dummy into the required seating
position, which remained constant for all simulations.
For a number of simulations a 50th percentile male dummy was used to replicate the
characteristics of a mid-sized male driver. A slightly different posture was used for
the 50th percentile to take into consideration the change in leg length from the 5th
percentile.
5.1.2. Seat
The seat was modelled as two planes, with no headrest included. The geometry of the
seat model was obtained from taking measurements of a Ford Mondeo vehicle. Care
was taken to ensure that a standard seating position was modelled, with respect to any
physical height adjustments that the seat was capable of achieving. The angle of the
seat back and height of the seat from the floor were also measured and kept constant
throughout the simulations. The floor measurement was necessary to ensure that the
feet were in the correct position to make a flat contact with the floor. A suitable
stiffness characteristic was chosen to replicate the cushioning effect from the seat
cushion, as no specific data from a Ford Mondeo was available. These values were
obtained from a previous research project.
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5.1.3. Airbag properties
The airbag model was taken from a previous research project conducted by CIC and
represented a driver’s size airbag with venting holes. The bag was folded and stowed
away within the steering wheel, but without a cover. The model had been proven in
previous work that it replicated the size of a 1st generation airbag and was stable and
robust.
To determine the inflation characteristics for the airbag such as mass flow rate and
temperature constants, various companies, including Autoliv, were contacted for their
advice and comments. A standard mass flow rate was agreed upon that represented a
1st generation airbag from the 1997 era and was subsequently used in the simulations.
Figure 62
Figure 62. Airbag Mass Flow Rate
5.1.4. Seatbelt Properties
The seatbelt was modelled as a three-point harness to replicate a seatbelt system
which would have been in operation in 1997, with no pre-tensioner. The seatbelt
elements were modelled with a series of spring type elements at the locations when
the belt passed through the slip-ring at the shoulder anchorage position and at the
buckle. At other locations where the belt passed over the dummy, a more detailed
shell mesh was used to enable a more accurate interaction between belt and dummy.
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As there was no pre-tensioner fitted, the seatbelt anchorage points remained constant
throughout the simulation.
Similarly to the airbag, the seatbelt properties were approved by Autoliv as
representative of a typical vehicle restraint system and would be suitable for use in a
FE model.
In each different seating position, the seatbelt was re-draped and fitted to the dummy
due to the changes in anchorage points. This was necessary to ensure that there was a
reasonably tight fit between seatbelt and dummy.
5.1.5. Measurement of Chest to Steering Wheel
After positioning the dummy in a standard seating posture, it was necessary to
position the steering wheel at set locations from the dummy. A measurement was
made from the centre of the chest (sternum location) to the centre of the steering
wheel, Figure 63. This dimension was used to determine the different seating
positions and adjusted by moving the steering wheel, floor, dashboard, upper seatbelt
anchorage point and seatbelt retractor along the fore/aft axis of the vehicle. The range
of motion of the different seating positions was between 430mm to 105mm. Beyond
the 430mm position the 5th percentile driver would have difficulty in reaching the
steering wheel with their hands, as well as reaching the pedals with their feet. If the
dummy was moved closer than the 105mm position the lower part of the steering
wheel came into contact with the abdomen of the dummy. Between these two
extremes of 105mm and 430mm four positions were set, making a total of six seating
positions. The general simulation set up is shown in Figure 64.
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Figure 63 Sternum to steering wheel measurement
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Figure 64 Simulation set up
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5.1.6. Pulses
The aim of the project was to determine the performance of the airbag in a full frontal
impact hence it was necessary to obtain a crash pulse for a 1997 Mondeo type vehicle
undergoing a full frontal crash rather than an off-set deformable crash to avoid the
complications of modelling an offset crash. A pulse was obtained from Autoliv for a
35mph crash pulse from an upper mid size car from 1995 into a rigid barrier. After
initial simulations this pulse was considered to be quite aggressive and it was scaled
down to 25mph.
In addition, later on in the project two further pulses were obtained from TRL from an
actual Mondeo frontal impact into a rigid barrier at 21mph and at 35mph. Upon
reflection it was decided to include the aggressive 35 mph pulse so as to generate a
‘worst case scenario’. The two TRL pulses were subsequently used in addition to the
Autoliv 25mph pulse to generate a broad range of crash pulse speeds.
All three acceleration pulses were integrated to obtain their relevant velocity and then
applied to the model. The three pulses are shown in Figure 65 below.
Figure 65. Velocity Crash Pulses
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5.2.
Sept 2003
Simulation matrix
Using the three crash pulses an initial simulation matrix was devised. This matrix
totalled fifteen simulations, which allowed for extra simulations to be conducted at the
end of the project. A decision would then be made as to the most suitable choice
depending on the outcomes of the first fifteen conducted simulations. The simulations
covered a broad range of seating positions and crash pulses to ensure that any trends
in the dummy injuries incurred, would be highlighted during the programme of work.
The range covered by the sternum to steering wheel distance was chosen according to
the human factors assessment results. The average distance from the assessment of
smaller drivers was used together with one and two standard deviations either side of
this distance.
In addition to the 15 simulations originally devised it was decided to conduct a
number of extra simulations. These included:
•
Three simulations at the 105mm chest to steering wheel position,
with the three crash pulses of 21, 25 and 35mph.
•
Three simulations using a 50th percentile dummy at the
265/320/375mm chest to steering wheel position, with a crash
pulse of 25mph.
•
Two simulations with no airbag present using a 5th percentile
dummy at 265mm chest to steering wheel position, with two crash
pulses of 21mph and 25mph.
Thus, in total a matrix of 23 simulations were conducted. These are summarised in
table 57
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Table 57 Simulation matrix
Pulse
Dummy
5th percentile
female with airbag
5th percentile
female no airbag
th
50 percentile male
with airbag
5.3.
Chest to
hub (mm)
35 mph TRL
25 mph
Autoliv
21 mph TRL
105
3
3
3
210
3
3
3
265
3
3
3
320
3
3
3
375
3
3
3
430
3
3
3
3
265
3
265
265
3
320
3
375
3
Results
5.3.1. Proximity to steering wheel
The results of the finite element modelling are presented in this section.
The fundamental argument that will be used to justify how close to the steering wheel
a person can sit is that there are situations in which it is disadvantageous to contact the
airbag during its deployment phase. In an ideal world the entire restraint system,
including pretensioners, load limiters and the airbag, would be tuned such that for any
crash event and any size of driver, the airbag would be at its fully deployed state at the
moment of head contact with the bag. This is the scenario that restraint manufacturers
are working towards with future advances in restraint technology. It could be argued
that avoiding a contact at the time when the airbag reaches peak pressure would be
sufficient, however there could well be a period of time either side of this peak when
the ‘bag would still be considered an aggressive structure in terms of injury outcome.
Hence, the recommended chest to steering wheel distance will be such that the
head does not contact the bag until it is fully deployed.
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The simulation results have established the chest to steering wheel distance required
that ensures a head strike with a fully deployed airbag for each crash pulse, 35 mph,
25 mph and 21 mph. Again it is emphasised that these results apply to the 5th
percentile female dummy and to the given crash pulses and airbag. Variations in the
results would be expected for alterations to these variables.
Figure 66 shows how the volume of the airbag varies with time. It can be seen from
the graphs that for each of the pulses the airbag reaches it maximum volume, and
hence is considered fully deployed, after 0.05 seconds. The time line begins when the
pulse is applied to the model. There is a short delay of around 0.01 seconds before the
airbag starts to fire. There is then a period, lasting 0.03 seconds when there is a rapid
increase in the volume of the airbag this being the period when the airbag is inflating.
Between 0.04 and 0.05 seconds there is still an increase in the volume of the airbag
until the maximum is reached at 0.05 seconds. However during this period the rate of
increase is significantly slower and it is felt that there would be little risk of the airbag
causing an injury if a contact was made at this stage. Thus, ideally the head should
not be in contact with the airbag until 0.05 seconds after the start of the simulation,
but a contact after 0.04 seconds would be acceptable.
Figure 66 Rate of volume increase of airbag
21 mph volume
25 mph volume
35 mph volume
45000000
40000000
35000000
Volume mm^2
30000000
25000000
20000000
15000000
10000000
5000000
0
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
Time seconds
For each of the simulations, the exact point in time when the 5th percentile dummy
head first contacts the airbag has been recorded. These results are given in table 58.
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Table 58 Time till head contact on airbag
Time to head contact with airbag (ms)
35 mph
25 mph
21 mph
Chest to hub
(mm)
105
210
265
320
375
430
18.8
31.1
40.5
48.3
55
70.2
18.8
29.5
40.8
48.2
56
62.3
19.1
31.6
50.3
56.7
65.5
70.2
It is expected that a positive linear relationship would exist between the chest to hub
distance and the time to head contact with the airbag, i.e. as the chest to hub distance
increases so does the time taken for the head contact to occur. This certainly appears
from the data in table 58 to be the case. In order to be sure that an extrapolation can be
made from the data for any chest to hub distance falling within the modelled range,
linear regression has been used for each pulse to determine the strength of the
relationship and to plot the best fit line to the data. The results of the regressions are
given in table 59.
Table 59 Strength and significance of linear regressions
Regression coefficient (R)
Significance (p)
35 mph
0.990
< 0.001
25 mph
0.995
< 0.001
21 mph
0.985
< 0.001
The regression coefficient gives a measure of how well the regression line fits the
original data. If there were a perfect fit, then the regression coefficient would be equal
to 1. The significance of each regression is given by the associated ‘p’ value. The
closer to zero this value is, the more significant the regression. In all three cases
presented in table 59 the regressions are highly significant and the regression lines fit
the data extremely well. It is therefore appropriate to extrapolate from the data for any
steering wheel to hub distance within the range of the original simulations.
In order to determine the appropriate chest to steering wheel hub distance required for
a head strike to occur either 0.04 or 0.05 seconds into the crash phase, the lines of best
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fit given by the linear regression have been plotted and the distances relating to head a
contact at 0.04 and 0.05 seconds extrapolated.
The plots for each of the pulses are given in figure 67, 68 and 69. The vertical lines
mark the hub to chest distances at 0.04 and 0.05 seconds. The results are summarised
in table 60.
Table 60 Chest to hub distance for airbag/head contact at 0.04 and 0.05 seconds
Pulse
35 mph
25 mph
21 mph
0.04 seconds
258 mm
263 mm
231 mm
0.05 seconds
323 mm
325 mm
291 mm
Table 60 shows that ideally a chest to steering wheel distance of around 32 cm
should be recommended and that the minimum acceptable should be 25 cm.
Figure 67 Relationship between chest to hub distance and time of head to airbag
contact for 35 mph pulse
Simualtion points
Regression line
80
70
60
Time ms
50
40
30
20
10
0
0
50
100
150
200
250
300
350
400
450
500
Hub to chest distance mm
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Figure 68 Relationship between chest to hub distance and time of head to airbag
contact for 25 mph pulse
Simulation points
Regression line
70
60
Time ms
50
40
30
20
10
0
0
50
100
150
200
250
300
350
400
450
500
hub to chest distance mm
Figure 69 Relationship between chest to hub distance and time of head to airbag
contact for 21 mph pulse
Simulation points
Regression line
80
70
60
Time ms
50
40
30
20
10
0
0
50
100
150
200
250
300
350
400
450
500
Hub to chest mm
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It should be noted that a series of 3 simulations were performed using the 25 mph
pulse and substituting the 50th percentile male dummy for the 5th percentile female.
These simulations were carried out with chest to steering wheel distances of 265mm,
320 mm and 375mm. In each simulation using the 50th percentile male, the head
contact for corresponding distances occurred later than for the 5th percentile female.
This implies that to achieve a head strike with the airbag at exactly 50 or 40 ms into
the crash phase, the 50th percentile male needs to sit further forward than the 5th
percentile female. This is likely to be because of the additional height and subsequent
altered head trajectory in relation to the positioning of the airbag that the 50th
percentile male has over the 5th percentile female. Importantly, the recommended
distance for the smaller driver will not put the larger occupant at an increased
risk of contacting a deploying airbag should they choose to follow the same
guideline.
5.3.2. Injury outcome
An examination is now made of the how injury outcome varies with seating position.
The aim of this analysis is to establish whether or not the recommended distance turns
out to be detrimental in terms of injury outcome. It is emphasised again that whilst
less risk of injury might be perceived at closer distances, it is still acknowledged that
contact with a deploying airbag can be extremely disadvantageous in certain
circumstances and so this situation should be avoided.
This is a somewhat more complicated analysis as limitations within the model will
have a bearing on the extent of the severity predicted. Such limitations would include
the lack of pretensioners and load limiters and also a lack of restraint tuning in terms
of the interaction of the belt system with the airbag system. Other factors, also
mentioned in the previous section, are the properties of the seat and seatbelt used in
the modelling. Ideally a manufacturer would not wish for peak loads from a number
of sources to affect the same body region at the same time and tuning of the systems
enables the forces due to different components to be distributed throughout the crash
phase. It was not possible to incorporate this level of fine tuning into the simulations.
However, it is prudent to examine the injury outcome to verify that there are no
sudden increases in the risk of injury at the recommended distance.
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The relationship between the loads experienced by the dummy recorded as HIC15,
Head acceleration, Chest acceleration, Chest deflection, and Neck extension are
presented in the following figures. The results for the 5th percentile dummy in each of
the pulses are shown together with the 50th percentile male dummy experiencing the
25 mph pulse and the two simulations where no airbag was present. The full
simulation results including pelvis loads, not relevant to this discussion, are given in
Appendix 5.
Head injury
Figure 70 shows the relationship between HIC15 and seating position
Figure70 Relationship between HIC15 and seating distance
35 mph
25 mph
21 mph
50th 25 mph
25 mph no air bag
21 mph no airbag
1400
1200
1000
HIC
800
600
400
200
0
0
50
100
150
200
250
300
350
400
450
500
Chest to hub mm
Figure 71 shows the relationship between head acceleration and seating position.
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Figure 71 Relationship between head acceleration and seating distance
35 mph
25 mph
21 mph
50th Male 25 mph
25 mph no bag
21 mph no bag
100
90
80
70
(g)
60
50
40
30
20
10
0
0
50
100
150
200
250
300
350
400
450
500
Chest to hub
The general trend is for the HIC 15 value and the head acceleration to increase as the
dummy moves further away from the steering wheel although for the 25 mph crash
pulse the highest HIC is seen at the 105 mm seating position. On the whole though the
pattern is similar the actual readings are lower for the 50th percentile male than for the
5th percentile female. The readings obtained when no airbag is present are fractionally
lower than when the airbag is included in the model. At the 265 mm position, the head
did not make a contact with the steering wheel indicating that head strikes upon the
steering wheel are only likely at distances closer than this.
The results for the 35 mph pulse are unexpectedly high even when the severity of the
pulse is taken into account. It has not been possible to identify an explanation for this
result, but it is thought that the severity of the pulse may be stretching the boundaries
of the model set up.
There is a plateau in the readings at and around the proposed distances where for the
25 mph and 21 mph pulses the HIC 15 remains around 550 and the head acceleration
remains around 55 g. The HIC 15 values indicate a risk of both skull fracture and AIS
4+ head injury of 2% (figure 72 and 73).
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Figures 72 and 73 show the injury risk curves for skull fracture and AIS 4+ brain
injury in terms of HIC15.
Figure 72 Risk of Skull fracture by HIC 15
Figure 73 Risk of AIS 4+ Brain injury by HIC 15
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All of the head injury results indicate that for the given model set up, there is benefit
in terms of head protection in sitting more forward than those distances proposed.
However it is stressed once again that the results presented are for a limited number of
pulses for a single crash condition and that it is not recommended that a head contact
should occur prior to the bag being in its fully deployed state.
It is not the case that there is an excessive increase in the risk of head injury for
the distances proposed.
Neck Injury
Figure 74 shows relationship between neck extension and seating distance
Figure 74 Relationship between neck extension and seating distance
35 mph
25 mph
21 mph
50th 25 mph
25 mph no airbag
21 mph no airbag
0
0
50
100
150
200
250
300
350
400
450
500
-10
-20
Nm
-30
-40
-50
-60
-70
Chest to hub (mm)
There are optimal points in terms of head extension at the 105 mm and 265 mm
distance for each of the crash pulses for the 5th percentile female and for the 50th
percentile male. The values at 210 mm are only moderately adverse in comparison.
The amount the neck extends during the crash phase is an increasing function with
distance since if more travel is required prior to the cushioning effect of the bag, more
extension of the neck will be experienced. At 430 mm the chin almost touches the
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chest and the airbag is only glanced, thus it would be expected that the amount of
extension and the velocity reached during the extension would be greater in this case.
Figure 75 Risk of AIS 3+ neck injury by neck extension
Figure 75 shows how the neck extension relates to risk of AIS 3+ neck injury. At the
265 mm position where the neck extension is between 30 and 40 Nm for the three
pulses the corresponding normalised values for the 5th percentile female are 1.2 and
1.6. These correspond to a risk of AIS 3+ neck injury of around 2-3%. At 320 mm the
extension corresponding to the 25mph pulse rises to 44 Nm with normalise extension
of 1.8 and risk of AIS 3+ neck injury of around 5%.
It is not the case that there is an excessive increase in the risk of neck injury for
the distances proposed.
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Chest Injury
Figure 76 shows the relationship between chest deflection and seating distance
Figure 76 Relationship between chest deflection and seating distance
35 mph
25 mph
21 mph
50th Male 25 mph
25 mph no bag
21 mph no bag
80
70
Chest deflection (mm)
60
50
40
30
20
10
0
0
50
100
150
200
250
300
350
400
450
500
Hub to chest (mm)
There is a substantial increase in the deflection of the sternum at the closest seating
position when compared with those from 210 mm outwards. In the 210 mm to 430
mm range the sternum deflection remains fairly constant for all the pulses, with the
value for the 35 mph pulse being a little higher than the 25 mph and 21 mph pulses.
The 50th percentile male incurs almost 20mm more deflection than the 5th percentile
female for equivalent crash conditions and this may be due to the increased mass of
the dummy.
Figure 77 shows the injury risk curve for AIS 3+ and AIS 4+ thoracic injury in terms
of sternal deflection.
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Figure 77 Risk of AIS 3+ and AIS 4+ Thoracic injury by sternal deflection
For the 5th percentile female dummy, a chest deflection of 40 mm becomes a
normalised deflection of 1.03 when considering AIS 3+ chest injury risk as a function
of chest deflection. This relates to a risk of such injury of around 5% (figure 77).
Similarly, the normalised chest deflection for an observed deflection of 40mm with
respect to AIS 4+ chest injury is 0.76. Figure 77 shows this to correlate with a risk of
such injury of around 0.2%.
It is not the case that there is an excessive increase in the risk of chest injury for
the distances proposed.
5.4.
Discussion
Overall, the simulations provided an accurate indication of the injuries expected from
seating the dummy at various positions from the steering wheel. The kinematics of the
21mph simulations are shown in Appendix 6. Although the model has been generated
from a variety of sources, it can be seen from the chest deflection results and the HIC
results for the 21mph pulse that the optimum seating position for a 5th percentile
driver would be in the 210mm position, closer than recommended based on avoiding a
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head contact with a deploying airbag. The complete set of injury data should be
considered when choosing an optimal seat position as well as a variety of crash
scenarios. Obviously the model reflects a certain vehicle and to exactly specify the
distance at which a 5th percentile is less likely to suffer serious injuries from an airbag
deployment requires investigation across the entire vehicle fleet. Different vehicles
should be examined in a wide range of seating positions and accident scenarios.
However, it would be a lengthy task to perform this investigation and be extremely
difficult to cover all scenarios. The simulations that have been modelled have
attempted to capture a range of seating positions with three different accident
severities and trends have been identified from the work performed.
The models that have been used to assess the driver’s injuries have been constructed
based on a Ford Mondeo type vehicle. The pulse has come from a Mondeo crash and
the geometry has been measured from a vehicle of the correct age and style. In
addition, the airbag properties have been approved to be in the correct range for an
upper mid size type vehicle, although they have not been exactly specified as the
airbag which would be fitted to the vehicles used to derive the crash pulses.
Differences may occur between inflation and venting rates, which in turn would have
an influence on the dummy injuries.
Similarly, the seatbelt properties were approved for a Mondeo type vehicle, but where
not specific to the vehicles used to derive the crash pulses. The seatbelt plays an
equally important role with the airbag in restraining the occupant. Therefore, it was
necessary to co-ordinate their properties as closely as possible. For the vehicle
manufacture, the belt and bag properties are tuned so that they work together towards
providing the best possible restraint for the occupant in a wide range of accidents.
They will make sure that the belt does not provide too much load to the chest, by
perhaps using load limiters and timing the contact with the airbag so that the head is
cushioned, rather than allowed to strike the steering wheel.
If the airbag retains a reasonable pressure over a longer period of time, the chances of
the dummy’s head striking it whilst it is at this optimum pressure are increased. If the
head strikes the airbag when the pressure has dropped too substantially, the airbag
will not be able to act as an effective restraint mechanism. Alternatively, if the head
strikes the airbag in the initial stages of inflation when the pressure is increasing, the
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driver is likely to suffer from more serious injuries. In the case of small drivers the
chances of the airbag striking the occupant in the early stages of inflation are
increased because they are more likely to sit closer to the steering wheel. Therefore,
the timing of events is critical when investigating the use of restraint mechanisms in
crash scenarios.
Throughout the simulations the airbag has fired at the same time irrespective of the
crash pulse. In reality, the vehicle’s crash sensor would have detected the crash (and
possibly the position of the driver) and deployed the airbag at a time when it was most
advantageous. As the exact information was not available, the firing time for the
airbag was the same across all simulations. It maybe that in low speed collisions the
airbag will deploy later on in the crash sequence because the severity of the crash
pulse is not enough to fire the airbag. If the airbag does fire later, a closely positioned
occupant may be more likely to come into contact with a deploying airbag.
An analysis of the chest deflection results showed that at positions where the occupant
is sitting close to the steering wheel the deflection rose to 71mm for the 35mph
simulation. The chest deflection for each crash pulse was at its peak, when the dummy
was sitting at its closest position. This is partly due to the contact with the airbag as
well as the lower rim of the steering wheel. The 5th percentile dummy in this situation
is not fully bio-fidelic as it allows the steering wheel to push a large proportion of the
abdomen in towards the spine. In the real world, the steering wheel may provide a
more concentrated load and instead miss the rib cage resulting in soft tissue and
internal injuries to the driver.
The chest accelerations, reported in Appendix 5 showed similar levels of injury across
the different seating positions. The level was below the 60g criteria in all cases and
may indicate that the seatbelt was providing a supportive role to the chest independent
of the airbag firing. As the seating position moved away from the steering wheel, the
pelvis accelerations, reported in Appendix 5, showed a reduction in value in the
265mm and 320mm seating positions, for the 21mph simulations. The two
simulations at distances greater than 320mm showed a levelling off of the pelvis
acceleration peaks, which was likely to be caused by the lack of contact between the
airbag and pelvis, and would further indicate that the seatbelt was providing the main
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form of restraint. Further evidence of the seatbelt dominating the injury mechanisms
of the pelvis, is that the time of the peak pelvis accelerations were all similar.
The seat cushioning and positioning of the dummy on the seat is a factor to be
considered when analysing the results. The HIC is calculated on the resultant
acceleration and therefore all three components of the head, chest and pelvis
acceleration profiles are affected by the performance of the seat. The seat cushion,
with the chest and head to a lesser extent, directly affects the pelvis acceleration. If the
seat is too stiff, the dummy pelvis may experience a large deceleration during the
simulation, whereas if it is gradually cushioning the load of the dummy, the
acceleration may well be lower. The simulation results may be compromised by the
non-Mondeo properties of the seat base, although they are from a similar type vehicle.
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Regulatory Impact Assessment (RIA)
An integral part of this research project was the need to conduct a Regulatory Impact
Assessment (RIA) if elements of the conclusions and recommendations were likely to
place a greater burden on stakeholders.
In consideration of this, the following stakeholders were identified:
•
The driving population, made up of smaller drivers (as the subject of this
research) and those of medium or larger build.
•
The manufacturers of the UK automotive fleet
•
The distributors and retailers of vehicles in the UK
•
The suppliers of original equipment manufacturer (OEM) or aftermarket
accessories intended to facilitate the comfort and control of small drivers
•
Appropriate Government departments.
The conclusions of this research focus on information and education such that drivers
in general, and smaller driver in particular, are suitably informed so as to be able to
select a safe driving position.
This education requires the support of the motor manufacturers and retailers but is
unlikely to place additional burden upon them since the dissemination is intended to
be Government Agency led.
The scenario is proposed where the consumer is informed by public domain
information such that they both assess the suitability of new vehicles and ask pertinent
questions of the retailer. If the vehicle of interest does not appear to provide a suitable
range of driving positions, the consumer is prompted to enquire of the manufacturer
what additional adaptations are available or, indeed, whether this vehicle is unsuitable
for them. The consumer can then decide whether to explore any adaptations or to
consider an alternative vehicle from that, or another, manufacturer.
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In this scenario, it appears that there is additional burden upon the manufacturing and
retail trades, and that an RIA would be desirable. However, this is not substantiated if
the wider picture is considered.
Under current UK consumer protection law, the manufacturers and retailers of motor
vehicle (and, indeed, any other product) can only supply products that are ‘safe’.
Safety clearly has a wide range of connotations, however the ability to control the
vehicle through achieving a suitable driving position can strongly be argued to be
paramount to safety. This could be achieved by the manufacturer through initial
design of the vehicle, provision of suitable aftermarket accessories or the simple
expedient of consumer advice that a given vehicle is not suitable for consumers of
short stature. Clearly, any intervention must be reasonable, but such interventions are
already a legal requirement.
Certain onus falls on the consumer in ensuring that the manufacturer or retailer is
aware of their specific needs, and this element would be addressed in the provision of
the public domain information in instructing the consumer to ask the manufacturer
about seating adjustment. In other respects though, the recommendations contained in
this report place no further legal burden upon the identified stakeholders.
For this reason it is not considered necessary to undertake a Regulatory Impact
Assessment.
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Conclusions and Recommendations
The aim of this project has been to make an assessment of cars for small drivers. The
first question raised concerned just who constituted the small drivers for which the
assessment was to be made. Historically, ‘small’ has been considered the 5th
percentile female, but this representation by definition excludes 95% of the female
population and around 98% when considering drivers of both genders.
In order to determine who should be assessed within the small driver population, an
analysis of the accident data was made and the population defined according to risk of
serious injury. Sections of the population were isolated according to height as having
an increased risk of AIS 2+ injury when compared to the risk for the population in its
entirety, the ‘average’ risk of injury.
It was found that drivers up to a little over 160 cm in height had the highest rate of
AIS 2+ injury across all body regions, and a significant increased risk of AIS 2+ head
injury. This result applied to both men and women and so the entire lower quartile of
the population was chosen as the group for which the assessment should be made.
Whilst it is still concluded that the increased risk of injury exhibited by the smaller
drivers will in some part be attributable to their more forward seated position within
the vehicle, the data available was not able to support this premise.
In order to assess cars for the smaller driver a survey of 100 drivers in the lower
quartile of the population with respect to height was carried out. The following were
identified:
•
The driving position adopted and the reason for adopting that position,
•
The drivers access to primary and secondary controls,
•
The quality of the driver’s view of the road,
•
The driver’s knowledge of the range of driving position adjustment available
within their vehicle,
•
The driver’s views on the adequacy of their adjusted position and the
importance of the driving position in determining the selection of their vehicle,
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The driver’s awareness of the potential hazard presented by a close seating
position.
•
How far rearward a small driver can position themselves and whilst still being
able to reach the primary controls
In the sample, the first action of the driver when selecting their position was to slide
the seat backwards and forwards until the reach to the pedals was acceptable. This
indicates leg extension as a primary variable dictating the smaller drivers seating
position and that the provision of a suitable range of adjustment of either the seat or
the pedals is vital to being able to adopt an acceptable seating position. Next, adequate
reach to the steering wheel was obtained. For smaller drivers this could only largely
be controlled by adjustment of the seat back angle since their leg length reach was
restricted.
Vision from the vehicle is an important factor for smaller stature drivers and their
vision can be compromised especially for low speed manoeuvres.
It was found that smaller drivers do sit closer to the steering wheel that is the norm but
that this distance is only 8cm or so closer and that on average they chose to sit so that
their chest is 32 cm away from the steering wheel hub. All of the drivers in the survey
were able to achieve at least this distance when prompted to adopt an alternative
driving position but the alternative position was not popular on the whole. It was
shown that seating posture is learnt in a drivers established vehicle and that this
posture is maintained with a high degree of accuracy in a new vehicle. Given this and
the reluctance to change, improving posture through education or information will be
difficult.
Small drivers appear to have a lack of knowledge concerning the safety consequences
of sitting too close to the steering wheel and some believed that sitting closer to the
steering wheel is better for airbag performance. There was also a lack of knowledge
about steering wheel adjustment and some difficulty was found in operating the
adjusting controls.
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For those that seek advice, appropriate guidelines on how to achieve a suitable driving
position within the vehicle that realises issues concerned with vision from the vehicle
and that does not compromise crashworthiness should be available.
In terms of recommending suitable guidelines, one key issue remains: what is the
minimum permissible chest to steering wheel distance once an ergonomic driving
position has been assumed?
A review of the current NHTSA guideline revealed a lack of information concerning
the derivation of their 10 inch rule. Whilst it is not the intention to in any way
discredit the advice given out by NHTSA, it is appropriate to review the distance in
view of the differences that exist between the British and the North American car
fleet.
The basis of the new recommended distance is that it is still considered
disadvantageous in some instances to come into contact with an airbag during its
deployment phase and that the best protection is offered by a fully deployed airbag.
Finite element modelling was employed to determine the hub to steering wheel
distance required to ensure a head contact with a fully deployed airbag. The modelling
activity concluded the following:
•
Ideally a chest to steering wheel hub distance of 32 cm should be achieved. If
this is not possible then a permissible minimum distance is 25 cm.
•
This recommendation is founded upon modelling of the 5th percentile female
dummy in 35 mph, 25 mph, and 21 mph frontal, full overlap, rigid barrier
impacts.
•
The recommended distance does not place the 50th percentile male dummy at
an increased risk of an earlier head contact for the type of impact modelled.
•
Some of the simulations showed less risk of serious injury for distances closer
than the recommendation. It is still maintained however that in some
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circumstances other than those included in the simulations, contact with a
deploying airbag would be disadvantageous.
•
There was not an excessive increase in the risk of serious head, neck or chest
injury for the recommended distances when compared with other distances
simulated.
•
If a comfortable driving position that allows access to the controls is not
possible without bringing the driver into closer proximity than is
recommended then either a remedial action should be taken or another vehicle
considered. Ideally any remedial devices employed should be considered
suitable for that vehicle by the vehicle manufacturer.
•
The simulation results have highlighted that the timing of events such as
airbag deployment time and the properties of the seat belt are critical in
determining the optimal settings to reduce the injuries of a small driver.
•
By increasing the number of vehicles examined and the crash pulses applied,
greater confidence could be established in the recommendations presented
here.
A review of counter measures and remedial actions available to help increase chest to
steering wheel distance was carried out.
•
Variations exist in the amount of fore-aft adjustability and height adjustment
of the seat offered by the vehicle. A driver should be aware of the adjustability
available within the vehicle and may opt to try different vehicles with different
amounts of adjustability in order to find one that best suits that individual.
•
The same applies with respect to the adjustability of the steering column and
steering wheel.
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Pedal extenders can be purchased in order that better reach to the pedals can
be achieved. However, these are sometimes promoted for comfort purposes
only and their implications in terms of ease and safety use has not been
evaluated.
•
The safety implications associated with the use of cushions and booster
cushions in order to increase visibility from the vehicle and to improve
comfort has is not fully understood at present.
•
A driver can be made aware of the countermeasures available but advice
should still be sought from the vehicle manufacturer with regard to the
suitability of any device for the vehicle in question.
Finally a proposed set of guidelines for self assessment of a vehicle’s suitability for an
individual follows.
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Make sure you can get into and out of the vehicle without unnecessary strain or
the need to bend or twist your body uncomfortably.
Take the vehicle for a test drive for a good period of time – at least 15 minutes.
Double check while you are driving that you can reach all the controls and that
you do not find yourself twisting, straining or stretching, all of which may lead to
long term discomfort.
Once you are in the seat of the car try to adjust the seat to a safe, comfortable,
driving position. If the car is fitted with a driver’s airbag, do this by following
Steps 1 to 4 in this leaflet. If no airbag is fitted, adjust the seat that you can
comfortably reach the foot controls and the steering wheel.
Make sure that you can see a good distance from all the car windows. Remember
that when parking or undertaking slow manoeuvres you will need to see close up
to the vehicle, so check each window in turn to make sure that there are no
obstacles.
With your seat in the chosen position, make sure you can reach all the main
controls without stretching. Check each of the following controls in turn:
Remember to check the vision through the rear quarter windows – imagine that
you needed to change lanes on a motorway and needed look ‘over your shoulder’
Steering wheel
Clutch
Handbrake
Indicators
Lighting dip switches
Windscreen wipers
Lastly check that you can adjust all the mirrors (internal and external) to get a
good view of the road behind.
Advice for drivers in achieving a safe driving position
Footbrake
Accelerator
Gear lever
Lights ‘on’ switch
Windscreen washers
Horn
What to do if you can’t achieve a seating position that meets the
requirements of Steps 1 to 4, or where you cannot operate the controls as
described in this leaflet?
Make sure you can see the main instrument displays without stretching or
twisting. In particular ensure that you can easily see:
The speedometer
The water temperature gauge
The petrol Gauge
Any warning lights for main beam, oil pressure, brake systems and electrical
charging.
Firstly, contact the vehicle manufacturer to see if they make any special
equipment intended to overcome the difficulty. This may include height
adjustable seats, adjustable foot controls or other solutions.
If they do provide such an option make sure you test the model of car you are
interested in with the option fitted before buying. Go through the points in this
leaflet again in the modified car.
Make sure you reach the remaining controls from your normal driving position
with only minimal stretching if necessary. This includes the heating and
ventilation controls, the radio, cassette or CD player and any switches mounted on
the door of the car.
If the manufacturer does not offer any modifications or options you should
consider a different make or model of car which allows you to find a seating
position which meets the requirements outlined in this leaflet
Make sure you can see over any obstacles formed by structures within the car, for
instance the dashboard or the rear head restraints.
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Advice for
drivers in
selecting a safe
driving position
in airbag
equipped cars
Airbags need to act very quickly in
order to help prevent injury in
accidents. Because of this, there is
an area close to the steering wheel
where the airbag inflates rapidly. If
the driver is in this area there is a
risk of injuries from the inflating
airbag as well as the chance that the
airbag may not work as well as
possible.
This leaflet gives guidance on how
to select a seating position that will
ensure that the airbag has enough
room to work properly. By
following the four simple steps it
should be possible for all drivers to
obtain a driving position that is
comfortable but without increased
risk.
Sept 2003
Step 1
Step 2
Step 3
Sit in the car seat and slide it
backwards as far as possible whilst
still being able to fully depress the
clutch or accelerator. Make sure
you can operate the brake as well.
Recline the back of the seat from a
vertical position to one that means
that you can comfortably reach the
steering wheel without stretching.
Aim for your elbows to be at an
angle of about 45º to the horizontal.
If reclining the seat in this way
means that you have difficulty
seeing the road either raise the seat
using the seat height adjuster (if
fitted) or use a firm cushion to sit
on. Make sure the cushion doesn’t
have a slippery surface.
If your car has an adjustable steering
wheel, try to adjust it so that the
steering wheel points down. Whilst
this will not increase the distance
between yourself and the airbag, it
will help to point the airbag towards
your chest if you have an accident.
Insert graphic – Show seat base
movement rearwards
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Insert graphic – Show seat back
angle adjust rearwards and show
elbow at 45º
159
It might be that your car has a
steering wheel that moves toward or
away from you. If this is the case,
you can use this adjustment so you
don’t need to recline the seat as
much. This may be more
comfortable without placing you
any nearer the airbag.
Ergonomics and Safety Research LTD
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Sept 2003
This bar is XX cm in length and can be used to measure the
distance between your chest and the steering wheel
Insert graphic – Show steering
wheel adjustment in two planes
Step 4
Measure the distance from the base
of your breast bone to the centre of
the steering wheel. If it is less than
XX cm, go back through the four
steps and readjust the seat until a
minimum of XX cm can be
obtained. This will probably only
require very small changes to the
seat position. For convenience, this
leaflet is exactly XX cm long, so
you can use it to see when your seat
position is correct.
Insert graphic – show XX cm
between sternum and steering wheel
N.B. In all images ensure that the
occupant is belted.
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8.0
Future work
A further programme of work should be initiated to continue development of the 5th
percentile driver model. Specifically to:
•
assess the combination of the airbag and seatbelt in various vehicles and adjust
their properties to match specific vehicles;
•
update the modelling of the seat to fully represent the seat cushion and seatback;
•
analyse the airbag firing times for individual vehicles;
•
investigate neck injuries which may occur later on in the crash event;
•
assess the use of pre-tensioners and load limiters in vehicles post-1997 which
reflect the state of the art in restraint systems;
•
investigate the injuries detected by dummy models and relate them to injuries
observed from real world data;
•
conduct simulations with no seatbelt to get a worst-case scenario and isolate the
effect of the airbag.
•
vary the crash scenario to include late deployment events
Other further work should explore the special requirements of taller drivers. The accident
data showed this extreme of the population to be at an increased risk of a serious head
injury in frontal impacts. Their requirements should be treated with equal importance as
those of the smaller driver.
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References
VSRC
Bittner, A C (1974). Reduction in user population as the result of imposed anthropometric
limits: Monte Carlo estimation (TP-74-6). Point Mugu, CA: Naval Missile Centre.
Crandall, J R; Martin, P G; Bass, C R; Pilkey, W D; Dischinger, P C; Burgess, A R;
O’Quinn, T Dschmidhauser, C B. Foot and Ankle Injury; The Roles of Driver
Anthropometry, Footwear and Pedal Controls. Proceedings of the 40th Conference of the
AAAM, Vancouver, Canada, October (1996)
Cullen, E; Stabler, K M,; Mackay, G M and Parkin, S. How People Sit in Cars: Implicatins
for Driver and Passenger Safety in Frontal Collisions – The Case for Samrt Restraints.
Proceedings of the 40th Conference of the AAAM, Vancouver, Canada, October (1996)
Dalmotas, D J; Hurley, J; German, A and Digges, K. Airbag Deployment Crashes in
Canada. In Proceedings of the 15th Enhanced Safety in Vehicles Conference, Melbourne
Australia, (1996)
Dischinger, P; Cushing, B and Kerns, T. Lower Extremity Fractures in Motor Vehicle
Collisions – Influence of Direction of Impact and Seat Belt Use. Proceedings of the 36th
AAAM Conference, Illinois, US (1992)
Evans, L and Frick, M C; Seating position in Cars and Fatality Risk. American Journal of
Public Health, 78:1456-1458. (1988)
Evans, L. Traffic Safety and the Driver. ISBN 0-442-00163-0 Published by Van Nostrand
Reinhold, New York, US (1991)
Ginpil, S and Attwell, R. A Comparison of Fatal Crashes Involving Female and Male Car
Drivers. Report no OR14, Federal Office of Road Safety, Canberra, Australia (1994)
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Grandjean, E; Sitting Postures of Car Drivers from the Point of View of Ergonomics. In
Oborne, J and Levis, J A (Eds) Human Factors in Transport Research, Vol 2 pp205-213,
London: Academic Press (1980)
General Motors, 2000; http://www.gm.com/cgi-bin/pr_display.pl?1137
Haslegrave, C M An anthropometric survey of British drivers Ergonomics Vol.22, No 2,
145-53
Hill, J R and Mackay, G M; In-Car Safety of Women. DETR Reference No. DPU9/72/20
(1997)
McFadden, M; Powers, J; Brown, W and Walker, M. Vehicle and Driver Attributes
Affecting Distance from the Steering Wheel in Motor Vehicles. Human Factors Vol 42, No
4, pp676-682. (2000)
Leiser, R and Carr, D (Eds); Analysis of Input and Output Devices for In-car Use
DRIVE Project V1041 (1991)
Nissan,
2002;
http://www.nissan-global.com/EN/STORY/0,1299,SI9-CH-LO3-TI453-
CI382-IFY-MC109,00.html
MSN, 2002; http://carpoint.msn.com/advice/news_495269_6.asp
Open Ergonomics; Peoplesize 1997
Parkin, S; Mackay GM and Cooper A. How Drivers Sit in Cars. Proceedings of the 37th
AAAM Conference, San Antonio, Texas, USA (1993)
Pheasant, S; Anthropometrics - An Introduction. ISBN 0 580 18234 7 Published by BSI,
Milton Keynes, UK. (1990)
Pheasant, S; BodySpace – Anthropometry, Ergonomics and Design Published by Taylor &
Francis 1988 ISBN 0-85066-352-0
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Porter, J M and Porter, C S; Occupant Accommodation; An Ergonomics Approach In An
Introduction to Modern Vehicle Design edited by Julian Happian-Smith ISBN 07506 5044
3 Published by Reed Educational and Professional Publishing Ltd, (2001)
Rebiffe R; General Reflections on the Postural Comfort of the Driver and Passengers;
Consequences on Seat Design. In Oborne, J and Levis, J A (Eds) Human Factors in
Transport Research, Vol 1 pp241-248, London: Academic Press (1980)
Richardson, J; Vehicle Ergonomics: Ergonomics of Displays. Vehicle Ergonomics MSc
Course Notes, Loughborough University (2001)
Stone, D L. Patterns of Gender Differences in Highway Safety. University of Wisconsin.
(1996)
NHTSA (1997) http://www.ou.edu/oupd/kidseat.htm
Van Cott, H P and Kikade, R G. Human Engineering Guide to Equipment Design .
Washington: Government Printing Office.
CIC
John D. Horsch, John W. Melvin, David Viano and Harold J. Mertz, “Thoracic Injury
Assessment of belt Restraint Systems on Hybrid III Chest Compression”, SAE Number
912895.
Nathaniel M. Beuse, William T. Hollowell, Lori Summers, Richard M.Morgan, Brian T
.Park, Taryn E. Rockwell, Jesse L. Swanson, “The 5th percentile Dummy in a 56kmph Full
Frontal barrier Crash Test”, Proceedings of 46th Annual Association for the Advancement
of Automotive Medicine” Sept-Oct 2002.
Steve Mark, “Effect of Frontal Crash Pulse Variations on Occupant Injuries”, Honda R&D
Americas USA Paper Number 400.
Michael S. Varat, Stein E. Husher, “Crash Pulse Modelling for Vehicle Safety Research”,
18th ESV, Paper 501.
Jos Huibers, Eric de Beer, “Current Front Stiffness of European Vehicles with Regard to
Compatibility” TNO Automotive Crash Centre, The Netherlands, Paper No. ID239.
Kennerly Digges, Ahmad Noureddine, Azim Eskandarian and Nabih E. Bedewi, “Effect of
Occupant Position and Air bag Inflation Parameters on Driver Injury Measures”,
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International Congress and Exposition, Detroit, Michigan, Feb 1998. SAE Number
980637.
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Appendix 1
Questionnaire for additional information from CCIS cases
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Stature and Driving Position
QUESTIONNAIRE
Study undertaken by:
Vehicle Safety Research Centre
School for Ergonomics and Human Factors
Loughborough University
For further information, or help with this questionnaire contact:
R. Welsh
Telephone: 01509 283300
The aim of this study is to improve occupant safety. The contents of
this questionnaire are absolutely confidential. Information identifying
the respondent will not be disclosed under any circumstances.
Thank you for your co-operation and help with this study
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SECTION 1
In the first part of this questionnaire you will be asked to take some body
measurements. These measurements should be taken while you are sitting
upright. If possible a friend or relative should help you. It is important that
the measurements are as accurate as possible so that there is consistency
between respondents - the photographs will help you make the correct
measurements. A tape measure is enclosed for your use; please give
measurements in centimetres (cm).
1.1
Lower arm
Please measure the distance from
your wrist to your elbow (see
photo), and write the measurement in
the space provided.
Your may measure either your left or
right arm.
Locate elbow
joint
Locate wrist
bone
Lower arm measurement:
……………………………….cm
Measure this distance
1.2
Upper arm
Please measure the distance from your
elbow to your shoulder joint (see photo),
and write this measurement in the space
provided.
Your may measure either your left or right
arm.
Locate shoulder
joint
Measure this
distance
Upper arm measurement:
……………………………...cm
Locate elbow
joint
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Lower leg
Place your feet (without shoes) flat on the
floor and measure the distance from the
floor to the top your knee (see photo).
Please write this measurement in the space
provided. You may measure either your left
or right leg.
Measure to top
of bended knee
Lower leg measurement
………………………………..cm
Measure this
distance
Place one end
of measure on
the floor
1.4
Upper leg
Please measure the distance from the
front of your knee to lower back (see
photo), and write this measurement in the
space provided. You may measure
either your left or right leg.
Upper leg measurement
………………………………cm
Measure this distance
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Sitting eye height
Measure to
eye level
Please measure the distance
from the seat surface to eye
level (see photo), and write this
measurement in the space
provided.
Sitting eye height
……………………………..cm
Measure this
distance
Place one end of
measure on top of
seat
1.6
Sitting height
Please measure the distance from
the seat surface to the top of
your head, and write this
measurement in the space
provided.
Sitting height:
Measure this
distance
…………………………….cm
1.7
Weight
What is your current weight?
…………………………….kgs or …………………………..st and lbs
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SECTION 2
In this part of the questionnaire you will be asked to take a measurement in
your car.
2.1
Do you currently drive a car? (please tick box)
Yes
'
(please go to question 2.2 below)
No
'
(please go to question 4.1 on page 8)
2.2
What is the make and model of the car you drive?
(e.g Ford Focus)
………………………………………………………………………
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Distance from steering wheel, when in normal driving position
Sit in the driver's seat in your normal driving position.
Place the tape measure on the
centre of the steering wheel and
bring the rest of the measure
towards you horizontally,
keeping the tape level (see
photo). Please note the
measurement when the tape first
touches you.
Distance from steering wheel
…………………………………cm
Measure this distance
2.4
Contact point
Example
x
Please mark on the diagram where
the tape measure contacted your
body
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SECTION 3
3.1
Choice of driving position
Please rank the following according to their influence on your choice of
driving position. We are interested in how you select your driving position.
1 is most important, for example if you consider visibility most important
rank this '1'. You may give more than one item the same rank.
Item
Rank
Reach to pedals
Reach to steering wheel
Visibility from vehicle
Reach to other items, (e.g radio, window control,
heater). Please state below which items may influence
your choice:
Please add any further comments about your choice of driving position:
3.2
Have you changed your driving position in any way since the accident
referred to in the covering letter?
(please tick box)
No
'
(please go to question 4.1 on page 8)
Yes
'
(please go to question 3.3 below)
3.3
Please explain how your driving position has changed, and why.
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SECTION FOUR
4.1
4.2
Would you be willing for a researcher to visit you to retake these
measurements as part of a quality control exercise? (Please tick box)
Yes
'
No
'
It would be useful to be able to contact you by phone if we have any
questions about any of your responses. Please supply daytime and
evening telephone numbers if possible.
Daytime phone number ………………………………………………
Evening phone number ……………………………………………….
You have now completed the questionnaire.
Please return the questionnaire using the pre-paid envelope provided. The
tape measure is yours to keep.
Thank you very much for your co-operation and help
with this study
The aim of this study is to improve occupant safety. The contents of this
questionnaire are absolutely confidential. Information identifying the
respondent will not be disclosed under any circumstances.
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Appendix 2
Survey data sheet
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GENERAL DETAILS
Participant
1. Name ………………………………………………
2. Gender ……………………………………………
3. Date of birth ……………………………………….
4. Years driving total…………………………………
5. Years driving this car……………………………..
Vehicle
6. Make ……………………………………………….
7. Model ………………………………………………
8. Age …………………………………………………
9. Whose car primarily is this ……………………….
PARTICIPANT ANTHROPOMETRY
10. Stature ……………………………………………cm
11. Upper arm length ………………………………..cm
12. Lower arm length ………………………………..cm
13. Upper leg length …………………………………cm
14. Lower leg length …………………………………cm
15. Sitting height ……………………………………..cm
16. Sitting eye height ………………………………...cm
REACH TO CONTROLS
Pedals
17. Rear of seat base centreline to middle of accelerator ……………………...cm
18. Rear of seat base centreline to middle of brake …………………………….cm
19. Rear of seat base centreline to middle of clutch …………………………….cm
20. Height of accelerator ………………….cm
21. Height of brake ………………………..cm
22. Height of clutch ……………………….cm
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Steering wheel
23. Seat back to furthest point of steering wheel ……………….cm
24. Seat back to middle of steering wheel ……………………….cm
25. Middle of steering wheel to clutch ……………………………cm
Gear stick
26. Rear of seat base centreline to most forward throw of gear stick ……………….cm
HVAC
27.
Rear of seat base centreline to furthest HVAC …………………cm
RANGE OF ADJUSTMENT
Seat travel
28. Seat front edge to clutch - foremost travel …………………..cm
29. Seat front edge to clutch - rearmost travel …………………..cm
Steering wheel
30. Normal position: Steering wheel centre to clutch – height …………………cm
31. Normal position: Steering wheel centre to clutch – longitudinal ………..…cm
32. Adjusted: Steering wheel centre to clutch – height : Min……….cm
Max………..cm
33. Adjusted: Steering wheel centre to clutch – longitudinal : Min……….cm
Max………..cm
Pedal
34. Non-adjusted: Steering wheel centre to clutch – height …………….…….cm (as for
normal)
35. Non-adjusted: Steering wheel centre to clutch – longitudinal …………….cm (as for
normal)
36. Adjusted: Steering wheel centre to clutch – height ……………..cm (Range……cm)
37. Adjusted: Steering wheel centre to clutch – longitudinal ……….cm (Range……cm)
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GENERAL SEATING MEASURES
38. Sitting height to ground …………………..cm
39. Sitting eye height to ground …………………..cm
40. Steering wheel to chest …………………..cm
41. Steering wheel to chest - contact point …………………..
42. Steering wheel centre to nasion …………………..cm (ask subject to hold tape on nasion)
43. Elbow angle ……………o
44. Hip angle ……………… o
45. Knee angle …………… o
46. Foot angle ……………. o
47. Distance from top of headrest to top of ears ……………………….cm
48. Distance from back of head to front of head restraint …………….cm
VISION
49. Rear of seat base centreline to closest forward view of road…………cm
50. Rear of seat base centreline to closest rearward view of road…….…cm
Distance from rear of seat base centreline to front of vehicle…………cm
Distance from rear of seat base centreline to front of vehicle…………cm
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POSTURE
51. Taking into consideration you reach to the pedals, steering wheel, gear stick and other
controls and also you view of the road and your seating comfort, overall how would you
rate your seat position
Very Poor
Poor
Acceptable
Good
Very Good
52. What do you like about your seat position?
-----------------------------------------------------------------------------------------------------------------------
53. How do you think that it could be improved?
………………………………………………………………………………………………………
….
………………………………………………………………………………………………………
….
54. Please rank the following according to their influence on your choice of driving position.
We are interested in how you select your driving position. (1 is most important, for
example if you consider visibility most important rank this '1'. You may give more than
one item the same rank).
Reach to pedals
‰
Reach to steering wheel
‰
Reach to gear stick
‰
Vision from car
‰
Other …………………………………………………………………………………………..
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KNOWLEDGE OF ADJUSTABILITY
Seat adjustability
55. Can you show me how you would move your seat forwards and backwards?
Doesn’t know
1
2
3
4
5
Difficult
1
2
3
4
5
Very confident
Easy
56. Can you show me how you would adjust your seat height? (No adjuster……….‰)
Doesn’t know
1
2
3
4
5
Difficult
1
2
3
4
5
Very confident
Easy
57. Can you show me how you would adjust your seat back?
Doesn’t know
1
2
3
4
5
Difficult
1
2
3
4
5
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Very confident
Easy
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58. Can you show me how you would adjust your seat base? (No adjuster……….‰)
Doesn’t know
1
2
3
4
5
Difficult
1
2
3
4
5
Very confident
Easy
Steering wheel adjustability
59. Can you show me how you would adjust your steering wheel? (No adjuster……….‰)
Doesn’t know
1
2
3
4
5
Difficult
1
2
3
4
5
Very confident
Easy
Pedal adjustablility
60. Can you show me how you would adjust your pedals? (No adjuster……….‰)
Doesn’t know
1
2
3
4
5
Difficult
1
2
3
4
5
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Very confident
Easy
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KNOWLEDGE OF AIRBAGS
61. Do you think that the benefit that you airbag gives you
a) Is the same regardless of the seat position
………………………………………………………………………………………………
..
b) Varies with the seat position
………………………………………………………………………………………………
..
62. If b),
where do you think that it is best to sit
………………………………………………………………………………………………
..
where do you think that it is worst to sit
………………………………………………………………………………………………
..
63. If answer is that close is bad, ask how close is OK …………………….cm/inches
ALTERNATIVE POSTURE
(START WITH SUBJECT AT REAR AND MOVE FORWARD TO FULLY DEPRESS
PEDALS)
64. Ask the participant to adjust their seating position so that they are sitting as far back as
possible although still able to drive. Ask To what extent would you be happy to leave
here now and drive home using this seat position
Very happy
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182
OK
Happy
Very Happy
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65. Elbow angle ………….. o
66. Hip angle …………….. o
67. Knee angle …………... o
68. Foot angle ……………. o
69. Steering wheel to chest …………….cm
70. Steering wheel centre to nasion ………..cm
71. Where do you obtain your information about vehicle safety
TV
‰
Magazines
‰
Manuals
‰
Friends
‰
Other
‰
PURCHASE
72. Is driving position a significant factor in your choice of car to purchase ?
YES………….
NO………….
If YES, how important on a scale of 1 to 10………………..
73. What other factors influence your purchase of a car? (Write down what participant says
and ask them to score those factors out of 10.
Factor
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Appendix 3:
Driver education – NHSTA
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How do I stay safe when I'm driving?
B
U
Since the risk zone for driver air bags is the first 2-3 inches of inflation,
C
placing yourself 10 inches from your driver air bag provides you with a
clear margin of safety. This distance is measured from the center of the
K
steering wheel to your breastbone. If you now sit less than 10 inches
L
away, you can change your driving position in several ways:
I
•
reaching the pedals comfortably.
N
G
Move your seat to the rear as far as you can while still
•
Slightly recline the back of the seat. Although vehicle designs
vary, many drivers can achieve the 10-inch distance, even with
the driver seat all the way forward, simply by reclining the
back of the seat somewhat. If reclining the back of your seat
U
makes it hard to see the road, raise yourself by using a firm,
P
non-slippery cushion, or raise the seat if your vehicle has that
feature.
A
N
D
•
If your steering wheel is adjustable, tilt it downward. This
points the air bag toward your chest instead of your head and
neck.
[In its published version, the brochure will be 10 inches tall
and will indicate that it should be placed between your
G
breastbone and the center of the air bag cover to check your
distance.]
E
T
T
I
N
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Wrong
Unbelted and too close
Use Seat Belts
Move Seat Rearward
Recline Back of Seat
Correct
Belted and 10 inches or more
Tilt Wheel Down
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Appendix 4:
Driver education – Insurance Institute for Highway Safety
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Most shorter drivers can
eliminate risk without deactivation
Minor seating adjustments help shorter
drivers sit farther away from airbags
Among drivers who use safety belts, the possibility of a serious airbag
inflation injury is cause for concern if there's less than 10 inches between
the belted driver and the steering wheel. Most drivers, even short ones,
normally sit with at least this much distance to the wheel. This is the finding
of new Insurance Institute for Highway Safety research that measured the
distance between the bottom of the breastbone and the steering wheel hub
for 587 volunteers seated in their usual driving positions in their own
vehicles.
Standardizing volunteers' heights and ages to the distribution of the adult
population, researchers estimate that about 5 percent of women sit less than
10 inches from the steering wheel. Even among short women (5 foot-1/2
inch or shorter), two out of three still sit at least 10 inches away.
"Most drivers need only buckle up to avoid the risk of a serious airbag
injury. Only a small proportion of belted drivers are potentially at risk," says
Susan A. Ferguson, the Institute's research vice president who directed the
study.
The findings vary with car size. About 40 percent of short women in large
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and midsize cars sat closer than 10 inches to the steering wheel, compared
with 27 percent in small cars. "This may be because the steering wheel and
accelerator pedal are about 2 inches farther apart in large cars than in small
ones," Ferguson notes. "When the pedal is located well under the instrument
panel, a driver has to sit closer to reach the accelerator."
A related Institute study involved 13 drivers, all 4 foot-8 inches to 5 foot-2
inches. Each was asked to sit in a comfortable driving position in 12
vehicles of varying sizes. Most chose positions at least 10 inches back from
the steering wheel, but 3 of the 13 failed to do so in one or two vehicles
even after being encouraged to move as far back as possible.
All drivers who sat too close had at least 9 inches to the wheel so, in most
cases, "only minor adjustments were needed to eliminate the risk of a
serious airbag injury," Ferguson explains. She suggests not only pushing the
seat back, if possible, but also tilting the steering wheel down and raising
the seat up to achieve 10 inches and still drive comfortably. Some cars have
telescoping steering wheels that can help with this.
For a copy of "Survey of Driver Seating Positions in Relation to the
Steering Wheel" by D. De Leonardis et. al., write: Publications, 1005 N.
Glebe Rd., Suite 800, Arlington, VA 22201.
Insurance Instute for Highway Safety
Airbag Main Page
This information page graciously provided by the Insurance Institute for
Highway Safety.
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Appendix 5
Full simulation results
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35mph Simulation Results
Simulation
Number
Distance from
Steering wheel to
Chest
Impact Speed 35mph
Clipped 3ms Clipped 3ms
HIC HIC Time- Head
Chest
Pelvis
Chest
Neck
Neck
Head Airbag
36
15 HIC15 Acceleration Acceleration Acceleration
Deflection Flexion extension Strike Pressure
ms
g
ms
g
ms
g
ms
mm ms Nm ms Nm
ms ms
ms
1165 546 42.7 50.45 27.80 58.60
54.30
52.30
59.30 71.50 58.20 55.2 32.2 -26.8 59.6 18.8
22.3
1
105mm
2
210mm
1032 796
56.1 71.40 61.20 56.80
52.50
54.60
50.90 41.90 70.20 24.7 97.2 -38.01 63.6
31.1
22.4
3
265mm
1025 906
58.7 80.00 63.10 56.60
55.00
51.30
50.30 43.60 72.70
13 82.7 -35.8 45.8
40.5
21.5
4
320mm
1197 1000
61.3 78.90 64.40 58.30
51.40
57.00
50.50 43.70 73.70 36.8 83.5 -44.0 53.7
48.3
21.8
5
375mm
1306 1082 61.50 79.70 68.70 49.50
49.60
52.20
51.90 41.20 74.00
42 76.7 -56.1 59.4
55
22
6
430mm
1687 1249 65.30 89.70 68.80 56.40
54.50
59.50
51.00 45.22 72.70 50.8 78.7 -59.4 59.2
70.2
22.8
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25mph Simulation Results
Simulation
Number
Distance from
Steering wheel
to Chest
Impact Speed 25mph
Clipped 3ms Clipped 3ms
HIC Time- Head
Chest
Pelvis
Chest
Neck
Neck
Head Airbag
HIC 36 15
HIC15 Acceleration Acceleration Acceleration
Deflection Flexion
extension Strike Pressure
ms
g
ms
g
ms
g
ms
mm ms Nm ms
Nm ms
ms
ms
1003 680
31 48.40 31.80 42.00
43.40
38.60
57.00 58.30 47.70 42.04 39.2 -34.1 64.7 18.8
24.6
7
105mm
8
210mm
616
402
49.8 50.50 61.90 41.90
48.50
38.11
44.60 36.90 70.30 23.1 89.6
9
265mm
606
501
57.5 56.80 61.30 40.20
47.70
38.70
10
320mm
696
532
59.1 57.60 62.20 45.70
49.10
11
375mm
883
547 61.50 59.10 67.10 36.40
12
430mm
721
553
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192
60
29.5
23.2
44.30 39.90 68.50 32.7
88 -33.4 47.2
40.8
22.9
47.50
50.40 41.80 72.70 10.06
80 -44.4 51.6
49.2
22.6
50.70
40.20
42.40 36.90 70.80 52.7 83.3 -38.0 52.3
56
23.4
52.20
45.20
50.70 40.40 72.60 44.9 91.3 -47.3 62.4
62.3
22.4
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21mph Simulation Results
Simulation
Number
Distance from
Steering wheel
to Chest
Impact Speed 21mph
Clipped 3ms Clipped 3ms
HIC Time- Head
Chest
Pelvis
Chest
Neck
Neck
Head Airbag
HIC 36 15
HIC15 Acceleration Acceleration Acceleration
Deflection Flexion
extension Strike Pressure
ms
g
ms
g
ms
g
ms
mm ms Nm ms
Nm ms
ms
ms
587 324 28.8 39.60 30.70 39.10
59.80
40.10
61.80 59.10 66.60 53.5 34.4 -29.3 69.9 19.1
22.6
13
105mm
14
210mm
449
347
62.8 47.50 67.00 45.00
61.20
36.70
59.40 35.30 77.30 29.4 93.3 -34.2 68.9
31.6
22.4
15
265mm
508
426
64.8 52.20 65.80 39.40
58.80
39.30
54.30 38.40 76.70 5.11 85.1 -26.9
53
50.3
23.4
16
320mm
598
489
66.4 60.40 69.90 48.20
56.90
44.40
56.60 39.30 79.70 35.9 91.6 -37.3 56.4
56.7
22.3
17
375mm
818
526 68.80 56.20 77.10 36.40
58.40
42.30
51.20 35.60 80.60 28.2 91.3 -38.1 67.6
64.5
22
18
430mm
890
484
61.80
43.40
56.80 41.10 79.70 22.1 84.5 -49.6
70.2
22.8
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EXTRA SIMULATION RESULTS
Simulation
Number
Distance from
Steering wheel
to Chest
HIC 36
HIC
15
Clipped 3ms Clipped 3ms
Time- Head
Chest
Pelvis
Chest
HIC15 Acceleration Acceleration Acceleration Deflection
ms
g
ms
g
ms
g
ms
mm ms
Neck
Flexion
Nm
ms
Neck
extension
Nm
ms
50th % Male
19
25mph
265mm
508
327 63.60 38.20 70.60 40.40 63.10 33.90 55.20 57.00 72.00
56.1
50th % Male
20
25mph
320mm
705
426 67.20 53.80 72.60 35.80 62.90 39.76 55.70 57.70 75.80
50th % Male
21
25mph
375mm
1024
575 73.90 53.10 72.00 40.88 63.80 43.16 57.50 53.88 73.70
No Airbag
22
21mph
265mm
482
364 65.70 52.95 69.10 38.34 60.30 40.52 52.70
33.4
77.5 64.99 92.30 -28.3
No Airbag
23
25mph
265mm
603
407
37.9
70.6
58.7 50.94
68.3 40.41
58.6
38.8
58.7
-37
47.4
44.4
23.8
21.8
84.7 -53.7
59.3
51.3
23.5
72.1
88.6 -58.3
59.8
57.4
24.8
42.9
91
72.5 -32.6
.
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Head Airbag
Strike Pressure
ms
ms
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N/A
50 N/A
N/A
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Appendix 6
Kinematics of 21 mph simulation
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Appendix 7
Paper presented at 46th AAAM Conference 2003
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THE EFFECT OF HEIGHT ON INJURY OUTCOME FOR
DRIVERS OF EUROPEAN PASSENGER CARS
Ruth Welsh, Andrew Morris
Vehicle Safety Research Centre
Loughborough University, UK
Laurence Clift
Transport Technology Ergonomics Centre
Loughborough University, UK
ABSTRACT
Statistical analysis of the UK in-depth accident database has been used to establish
the characteristics of the ‘small driver’ at increased risk of injury. Drivers less than
160 cm in height are shown to have a significantly higher than average probability of
AIS 2+ head and AIS 2+ pelvis and lower extremity injury. Subject trials have been
used to establish the seating preferences of small stature drivers together with a
comparison group drawn from the population as a whole.
It is a well-established fact that females are smaller in stature on average than
males. Research has also examined injury differences between males and females in
crashes. Evans (1998 and 1991) was able to show that for an impact of a given
severity, females aged 15 to 60 are more likely to be killed than males. He did not
however elaborate as to the underlying cause, although stature is thought to have been
a factor in addition to biomechanical and physiological difference. Stone (1996) also
found that female drivers were more likely to be injured than male drivers and the
reasons for this included the fact that females are generally shorter in stature than
males thus necessitating closer positioning to the steering wheel and also because of
‘inherent physical frailty’. He also observed that shorter drivers (both males and
females) had an increased risk of lower extremity fractures. This finding was
supported by Dischinger (1992); she noted that drivers less than average height in the
US (1.70 m or 5ft 7ins) had a 64% increase in lower extremity fracture rates with
most injuries being to the ankle/tarsals.
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Lenard (2001) showed female front occupants to be more vulnerable to injury in
frontal impacts, especially with regard to skeletal chest and leg injuries whilst
Crandall (1996) found that ‘shorter’ front seat occupants were also at greater risk of
lower limb injury with women having a higher risk than men. There have also been a
number of studies that have examined the types and mechanisms of injuries that can
be caused by airbags in certain situations. Kirk (2002) in an extensive review of the
benefits of airbags in European vehicles, showed the probability of AIS 2+ head
injury to be greatly reduced in airbag-equipped vehicles with shorter drivers having
the greatest benefit. However, in some circumstances it is possible to have
unfavourable interaction with the airbag during the early deployment phase resulting
in serious injury not least if the driver is in close proximity to the steering wheel prior
to impact.
Several observational studies have highlighted the differences in seating position
adopted by drivers of varying stature. Research in the UK (Parkin 1993) has shown
that for the population observed the 5th percentile female sits some 21.5cm closer to
the hub than the 95th percentile male, and the 50th percentile female over 6 cm closer
than the 50th percentile male.
It is evident that previous research has focussed in the majority upon gender based
analysis. It is accepted that gender and stature are unavoidably highly correlated
variables however a separate stature based analysis is warranted to establish what
differences exist in injury patterns when stature is considered as opposed to gender.
This paper considers how the risk of injury to belted drivers in the UK varies with
stature and investigates further the seating positions of those drivers in the population
seen to be at a higher than average risk of injury.
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The aims and objectives are summarised as follows;
To identify relationships between height and injury outcome for drivers of European
passenger cars;
To identify by height those members of the population with an increased probability
of serious injury compared with standardised probability across all heights
To investigate the relationship between height and seating position for those with a
possible increased risk of injury.
METHOD
The UK in-depth accident database (co-operative crash injury study), known as the
CCIS database has been used to investigate the relationship between stature and injury
outcome for belted drivers of passenger cars. The data are sampled on vehicle age,
vehicle damage and injury outcome. To be included in the database, the accident must
have included at least one car that was at most seven years old at the time of the crash,
was towed away from the accident scene and in which an occupant of the car was
injured The data are also collected within a stratified sample which is biased towards
‘fatal’ and ‘serious’ injury outcome crashes (KSI). Of those occurring within the
geographical sampling regions approximately 80% of all the KSI crashes, and around
10-15% of the slight injury outcome crashes are investigated.
Additional case selection has taken place for the analysis presented here. The data
is collected retrospectively and gathers information concerning injuries and
anthropometry from hospital records and questionnaires. Whilst an accurate record is
kept of a person’s injuries, it is frequently the case that their height has not been
noted, thus only around 45% of the drivers (those whose height is known) have been
included in this analysis.
The analysis considers the injury outcome for frontal crashes. An underlying
hypothesis in the research is that smaller drivers adopt a more forward seating
position than taller drivers and thus are closer to internal frontal structures such as the
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steering wheel and column. In a frontal collision both the occupant trajectory and the
possible intrusion upon impact make this the crash mode where there is most likely to
be a relationship between injury outcome and seating position.
In total 1,470 drivers are included in the analysis, around 65% male and 35%
female. Any further selections are noted in the text. The data covers the period 19922001.
The analysis results have been tested for statistical significance where appropriate
using Chi-Square tests. In each case, the null hypothesis of no difference between
groups is rejected if the probability (p) associated with the test statistic is less than
0.05.
Further to the analysis a survey has been carried out to determine the seating
preferences of those shorter drivers shown to have an above average risk of injury.
Drivers were observed in both their own vehicle and small family car. Key
measurements were made when in both their chosen driving posture and in that being
Welsh et al
2003
Page 3
the most rearward achievable whilst maintaining adequate reach to all of the controls.
In total 100 small stature drivers participated in the study. The survey was repeated on
a comparative group of 20 taller drivers.
The results presented form part of a study which aimed to assess the current car
fleet in terms of it’s suitability for small drivers and to recommend remedial actions
that could be taken by smaller drivers to address the issues raised. The first phase of
the work, and that presented here, was to determine, by height, that part of the
population most vulnerable to injury. Thus, the early analysis considers the entire car
fleet irrespective of supplementary restraint systems. However, all of the drivers
included in the analysis were belted and some of the later analysis considers airbag
fitted vehicles.
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RESULTS
Data Analysis - It has been mentioned previously that gender and height are highly
correlated variables. In general the female population is significantly shorter than the
male, this is also the case for the drivers included in this analysis (χ2 = 697.3, d.f=9, p
< 0.01). Figure 1 shows the distinctly bi-modal distribution of height within gender.
Table 1 provides key adult percentile measures taken from anthropometrical tables
(Pheasant 1990).
Figure 1 – Distribution of height by gender for drivers in sample
Female n=590
Male n=881
35%
30%
25%
20%
15%
10%
5%
0%
up to
150
151-155 156-160 161-165 166-170 171-175 176-180 181-185 186-190
>190
Height (cm)
Height (cm)
Male
Female
5th percentile
162.5
151
50th percentile
174
161
95th percentile
185.5
171
Table 1 – Adult height – percentile measures
It is clear that a stature-based analysis will inevitably become gender biased at the
extremes of the population. For both injured men and women (at all levels of injury
severity), the height distribution is skewed to the right of the 50th percentile. Initially,
this may indicate an increased propensity for sustaining injury by taller occupants.
However, it should be noted that many of those injured will have received only minor
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injury (AIS 1 only) whereas the main focus of this study is examination of more
serious (AIS 2+) injuries.
An initial exploration of the impact characteristics of the accidents in the sample
was made to determine any differences in the direction of force of the impact and the
Delta-V when comparing shorter to taller drivers. No significant differences were
found.
Chi-Square tests have been used to establish where differences in the rate of AIS 2+
injury by height exist for the different body regions considered, these being the head,
chest, abdomen and pelvis and lower extremity as well as the Maximum Abbreviated
Injury Score across all body regions (MAIS). These variables were considered since
there were sufficient data for robust analysis. The two shortest and the two tallest
categories have been merged to ensure sufficient expected counts for valid results.
The results are summarised in table 2.
Body
region
Degrees
χ2
freedom
Significance (p)
MAIS
4.264
7
0.749
Head
17.582
7
0.014
Chest
4.602
7
0.708
Abdomen
7.313
7
0.397
19.390
7
0.007
Pelvis
and
lower
extremity
Table 2 - Chi-square tests for equal distribution of AIS 2+ injury within
height
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Based on the statistical results presented in Table 2, there are differences in the
rates of AIS 2+ injury within height for injury to the head and the pelvis and lower
extremity but not for MAIS, the chest or the abdomen.
Figure 2 shows the percentage of drivers within each height band who received an
AIS 2+ injury. For the head there appears to be a quadratic relationship between
MAIS
Head
Chest
Abdomen
Leg
40
% drivers AIS 2+
35
30
25
20
15
10
5
0
up to 155
156-160
161-165
166-170
171-175
176-180
181-185
>185
Height (cm)
height and rate of AIS 2+ injury. The shorter stature drivers have the highest rate of
serious head injury, those of medium height the lowest rate and there is subsequent
increase in the rate for the taller drivers. The smallest drivers have a significantly
higher rate of AIS 2+ pelvis and lower extremity injury than their taller counterparts,
whilst the second highest rate of AIS 2+ pelvis and lower extremity injury is found for
drivers between 170 and 180 cm tall.
Figure 2 - Rate of AIS 2+ by body region
The analysis has been repeated at the AIS 3+ level of severity for those body
regions where significant results were found at AIS 2+ level, that is the head and
pelvis and lower extremity.
Degrees
Significance
freedom
(p)
30.071
7
< 0.01
15.653
7
0.028
Body region
χ2
Head
Pelvis and lower
extremity
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Table 3 - Chi-square tests for equal distribution of AIS 3+ injury within
height
H ead
Leg
16
% drivers AIS 3+
14
12
10
8
6
4
2
0
up to 155
156-160
161-165
166-170
171-175
176-180
181-185
>185
H eight (cm )
Figure 3 - Rate of AIS 3+ injury by body region
As with AIS 2+ injury, a Chi-square test confirms significant differences in the
proportion of drivers with AIS 3+ injury for the different height bands (Table 3).
Figure 3 shows that the rate of AIS 3+ head injury varies with height in a similar
pattern to AIS 2+ injury. The same is evident for AIS 3+ pelvis and lower extremity
injury. Clearly the smallest drivers have a significantly higher rate of such injuries
than taller drivers.
Next any differential effect of height between men and woman was studied using a
general linear model including the independent variables gender and height so that the
significance of the interaction could be determined. The results presented are for those
body regions whereby previous results revealed a statistically significant relationship,
specifically the head and lower extremity. Table 4 shows the results from this
analysis. A statistically significant interaction term was found only in the case of
lower extremity. No statistically significant interaction term was observed for head
injury. The numbers in the table are the associated ‘p’ values for each term in the
model.
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Independent variable significance
variable
Head
Height
Gender
Interaction term
0.00
0.56
0.52
0.11
0.60
0.04
severity
Lower ex
severity
Table 4 – Interaction Term for Head and Lower Extremity Severity
As can be seen from the table, in the case of head injury the effects observed is due
to height only whereas in the case of lower extremity injury, there is a more
complicated interaction effect between height and gender that may need further
exploration.
The next analysis examines the effect of the driver airbag on head injury outcome
and a comparison is made between drivers in vehicles fitted (but not necessarily
deployed) with an airbag and those in a vehicle with no airbag. The lines shown in the
graph denoting ‘Average fitted’ and ‘Average not fitted’ are reference values for
injury probability standardised across all heights. Thus it can be shown which height
categories have a higher than average or lower than average probability of injury in
each situation (i.e. airbag/no airbag). Figure 4 shows the results of this analysis. This
distinction has been made as airbags have been shown to reduce the incidence of
serious head injury in other studies (e.g. Kirk et al 2002).
For reference, Table 5 gives the distribution of airbag fitment by gender and within
height bands. The % given (to 1 dp) is that within gender.
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Height
(cm)
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Male (879)
Female (590)
Not
Fitted
Fitted
Up to
2
1
155
(0.2%)
(0.1%)
156-
5
8
160
(0.6%)
(0.9%)
161-
11
26
165
(1.3%)
(3.0%)
166-
25
66
170
(2.8%)
(7.5%)
171-
66
131
175
(7.5%)
(14.9%)
176-
85
173
180
(9.7%)
(19.7%)
181-
69
120
185
(7.8%)
(13.7%)
Over
34
57
185
(3.9%)
(6.5%)
297
(33.8%)
Total
Fitted
15 (2.5%)
35 (5.9%)
40 (6.8%)
52 (8.8%)
30 (5.1%)
15 (2.5%)
0
Not
Fitted
42
(7.1%)
86
(14.6%)
107
(18.1%)
109
(18.5%)
35
(5.9%)
22
(3.7%)
1
(0.2%)
1 (0.2%)
0
582
188
402
(66.2%)
(31.9%)
(68.1%)
Table 5 – Airbag fitment by height and gender
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Figure 4 - Probability of AIS 2+ head injury by height and airbag fitment
Fitted
Average Fitted
Not fitted
Average Not Fitted
Probability of AIS 2+ head injury
0.25
0.20
0.15
0.10
0.05
0.00
150
155
160
165
170
175
180
185
190
Height (cm)
Firstly considering vehicles not equipped with airbags, Figure 4 shows that drivers
up to 160 cm in height have a significantly increased probability of AIS 2+ head
injury above the average for such vehicles. This is supported by a Chi-square test, χ2
= 17.865, p=0.013, d.f=7. On the whole drivers of medium stature have a lower than
average probability of serious head injury. For the tallest drivers, over 185 cm in
height, the probability increases above the average.
The picture is slightly different for air bag fitted vehicles. It is clear from Figure 4
that the probability of AIS 2+ head injury is lower for drivers of all statures in airbag
fitted vehicles than in those not fitted with airbags with one notable exception. In the
161-165 cm height band the data suggests that there is a higher probability of AIS 2+
head injury in an airbag fitted vehicle than in a non-airbag fitted vehicle. In airbag
fitted vehicles the probability of AIS 2+ head injury is above average for drivers up to
165 cm tall and also for those over 180 cm tall, whilst the probability of such injury is
below average for drivers between 166 and 180 cm tall. A Chi-square test shows
border line significant differences in the rate of injury for these three height groups in
airbag fitted vehicles. (χ2 = 5.722, p=0.057, d.f=2).
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Figure 5 – Probability of AIS 2+ pelvis and lower extremity injury by
height and gender
all drivers
average
Probability of AIS 2+ leg injury
0.25
0.2
0.15
0.1
0.05
0
150
155
160
165
170
175
180
185
190
Height (cm)
For AIS 2+ pelvis and lower extremity injury, Figure 5 shows that the smallest
drivers, up to 155 cm tall, once again have the highest probability of serious injury.
This group have a significantly higher than average probability of AIS 2+ injury (χ2 =
19.390, p=0.007, d.f=7). These will undoubtedly comprise mainly female drivers.
There is also an above average probability of AIS 2+ pelvis and lower extremity
injury for drivers between 170 and 180 tall.
The results presented above were used to make a judgement concerning the small
driver population considered to be above average risk of injury, these forming the
population of interest for the subsequent trials. It is evident that this population
extends beyond the stature of the 5th percentile female (around 150cm) and includes a
proportion of men. Keeping the focus on ‘small stature’ the entire lower quartile of
the European population was chosen, irrespective of gender. This equates to drivers
161 cm tall or less. The data presented raises issues for other sections of the
population; tall stature drivers with respect to head injury, and those of medium height
for pelvis and lower extremity injury, but they were not the focus of the trials which
looked for evidence of increased proximity to the steering wheel for small stature
drivers.
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Seating Preferences - In order to determine the preferred seating position of
smaller drivers, 100 subjects were recruited through advertisement in local media and
participated in a survey study. As this group was randomly self-selected from the
local population, it is proposed that the sample is representative of the general
population. The selection criteria were that the individual was at most 161 cm in
height and that they regularly used a vehicle (one individual was in fact, 162cms in
height). Because of the height requirement, the sample was heavily biased toward
female participants, who make up a large percentage of the smaller UK adult
population. Accordingly, 96 participants were female and only 4 male. In order to
provide an appropriate context for the small driver dimensions, a limited sample of 20
taller drivers were also appraised in the same manner. These were made up from 12
males and 8 females. Table 6 shows the population statistics for the small driver
participants and the control group, referred to as ‘normal’.
Stature
Minimum
Mean
Maximum
[stature %ile]
cm (ft)
cm (ft)
cm (ft)
Small drivers
140 (4’
154 (5’
162 (5’ 4”)
7”)
½”)
[26.5]
[0.03]
[5.4]
Normal
161 (5’
175 (5’
193 (6’ 4”)
drivers
3”)
9”)
[99.7]
[23.1]
[72.8]
Table 6 – Population statistics for participants
For each participant, four seating positions were evaluated representing the
participants chosen position, and the rearmost practicable position, for their own and a
reference vehicle. A limited number of static anthropometric measurements were
taken as well as some subjective data regarding attitudes to driving positions. These
data were correlated in order to determine compare the participant’s anthropometry
with the position they adopted in a vehicle.
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Selection of driving position
Each participant arrived for the evaluation in their own vehicle, allowing for an
accurate determination of their normal driving position. Examples are shown in
Figure 6.
Figure 6 – Examples of participant’s chosen driving positions.
When asked to adopt their chosen driving position in the reference vehicle, it
became apparent that the procedure is normalised. Invariably, the fore/aft adjustment
of the seat is adjusted for comfortable reach to the foot controls, followed by
adjustment of the seat back angle for comfort and reach to the steering wheel. Finally,
minor adjustments were undertaken to the lumbar support and height if required
and/or if the participant was aware of the facility.
This standardised procedure suggested that there is a clear relationship between
certain body dimensions and the proximity of the driver to various vehicle controls.
In particular, leg length and arm reach appear to be the critical values.
Proximity to steering wheel
The focus of this survey was the proximity of the driver to the steering wheel when in
their chosen driving position as well as a position optimised for clearance. In order to
explore the risk of head injury through steering wheel contact, the distance from the
nasion to steering wheel hub centre was recorded as well as the chest to hub centre.
The data recorded for the participants chosen seating positions is summarised in Table
7.
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Own vehicle
Reference vehicle
Mean
Small
Normal
Small
Normal
seating
drivers
drivers
drivers
drivers
32.6 (5.5)
40.6 (5.6)
32.6 (5.1)
41.6 (3.9)
40.6 (5.0)
47.5 (4.5)
39.4 (4.1)
47.5 (4.3)
measur
es (cm)
Steering
wheel to
chest
(SD)
Steering
wheel to
nasion
(SD)
Table 7 – Steering wheel proximity measures for drivers
It can be seen that the small driver’s average preferred distance (32.6 cm) from the
steering wheel was significantly greater for the participants than that recommended by
NHTSA (25.4 cm), as well as that recorded by previous observational studies.
Participants were asked whether seating position was a factor in the performance of
airbags. The recorded response is shown in table 8.
Benefit dependent on seat
Yes
No
Small drivers
71 %
23 %
Normal drivers
91 %
9%
position ?
Table 8 - Perceived dependence of airbag performance on seat position
Furthermore they were asked where was best to sit in this regard, close to the steering
wheel, far from the steering wheel, half way between or other. The responses are
shown in Table 9. A high proportion of the small drivers were not confident to give a
response to this question.
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Far
Close
Centre
Other
Don’t
know
Where
best to
Small
sit
drivers
Where
worst
59 %
6%
3%
1%
41%
8%
58 %
0%
1%
43%
86 %
0
0
14 %
0%
0
86 %
0
14 %
0%
to sit
Where
best to
Normal
sit
drivers
Where
worst
to sit
Table 9 - Perceived best location to sit responses
The effect of adopting the most rearward seating position on the proximity to the
steering wheel was also noted. The data, given in Table 10, demonstrates that only a
small amount of increased clearance is observed despite the participant being required
to sit with their limbs at almost maximum extension.
Own vehicle
Mean
alternative
posture
Reference vehicle
Small
Normal
Small
Normal
drivers
drivers
drivers
drivers
36.8
44.6
36.4
45.3
43.4
50.9
42.1
50.2
Steering
wheel to
chest (cm)
Steering
wheel to
nasion (cm)
Table 10 - Alternative seating position dimensions
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DISCUSSION
At present, regulatory compliance testing of vehicles involves crash testing of
vehicles using a 50th percentile dummy. It is well known that several vehicle
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manufacturers choose to conduct evaluations of crashworthiness performance using
anthropomorphic dummies that generally represent population extremes (i.e. 5th and
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95th percentile). It is worth noting that none of the dummies used in conventional
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crash testing are thought to adequately predict lower extremity injury outcome whilst
the prediction of head injury has been the subject of much debate over the years.
This study indicates that in the UK sample studied, there is an enhanced risk of
injury to small stature occupants in real-world crashes in two main aspects, these
being head injury and lower extremity injury at both the AIS 2+ and AIS 3+ levels. It
should be reiterated that the data used are biased towards fatal and serious crash
outcomes therefore may not truly represent the injury risk to the general population in
its entirety. However, since all drivers in the sample were subject to the same
sampling criteria, useful comparisons can be made within the data.
To take the issue of lower extremity injuries first, the reasons for enhanced injury
risk are reported but largely not explored in this paper. Follow up studies are planned.
Firstly, it would be worth examining in closer detail the exact type of injuries that
smaller stature drivers sustain compared to their taller counterparts. One issue could
be that of posture of smaller occupants. Given the need for the driver to maintain
closer proximity to the steering wheel, there is an inherent probability that shorter
stature drivers are likely to drive with the patella region in the proximity of the front
facia or underneath the steering column. With this positioning comes an enhanced risk
of entrapment of the knee in the event of a crash which in turn may lead to axial
loading and compression through the lower limb in the event of intrusion of the
footwell. This is a common cause of lower extremity injury and was reported
elsewhere by Taylor et al (1997). Another possibility involves that of positioning of
the foot/ankle during driving. Crandall et al (1996) noted in a simulated braking study
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that shorter stature drivers and females in particular were more likely to lift the entire
foot from the accelerator to brake whilst taller drivers and males were more likely to
‘pivot’ the foot/ankle whilst maintaining contact with the floor. The lower extremity
injury risk for females was in part explained by differences in footwear since
women’s high-heel shoes exhibited static and dynamic instability. However, another
observation involved the fact that shorter stature drivers tended to exhibit more
plantarflexion of the foot/ankle, a possible factor in enhanced injury risk.
Another explanation could be that smaller stature drivers actually drive smaller
vehicles, which are thought to be more prone to extensive intrusion of the footwell
region in the event of a frontal crash. Further analysis of the data is necessary to
explore this possibility.
The issue of head injury is even more complex. The National Highway Transport
Safety Administration (NHTSA) recommends 10 inches (25cms) as the minimum
distance that drivers should keep between their breastbone and their airbags for
several reasons. They maintain that drivers who sit 10 inches away and buckle up will
not be at risk of serious air bag injury. The 10-inch distance is a general guideline
that includes a clear safety margin. The 10-inch distance ensures that vehicle drivers
start far enough back so that, between the time that pre-crash braking begins and time
that the air bag begins to inflate, the occupants will not have time to move forward
and contact the air bag until it has completed or nearly completed its inflation. The 10
inch-distance was calculated by allowing 2-3 inches for the size of the risk zone
around the air bag cover, 5 inches for the distance that occupants may move forward
while the airbags are fully inflating, and 2-3 more inches to give a margin of safety.
However, the observational studies conducted in this study evidently indicate that the
short stature driver has a seating position that far exceeds this recommendation.
However, it is also worth noting that Parkin et al’s observational roadside study found
that the driving UK female sits some 9.2cm closer to the steering wheel than the
position of the 5th percentile Hybrid III dummy in a crash-test. Therefore in order to
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gain a more complete understanding of why head injury risk is higher to the shorter
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stature driver, it is necessary to examine in more detail the both the mechanism of the
head injuries and also the source of the injuries. It may be necessary to also reexamine static positioning versus actual driving position as one possibility remains
that the position adopted by the driver immediately prior to the crash is somewhat
different to the position adopted in static observations. Therefore it is feasible that the
driver could potentially interact with the airbag at the point of deployment. Previous
work has indicated that there is some risk of concussive head injury in such an event
(Wellbourne, 1994). He also noted an anecdotal case of a dummy head striking the
steering wheel behind the deployed airbag. Even if the airbag is not directly
responsible per se for head injury, in some cases the possibility exists that close
proximity of the airbag in the crash could result in the head ‘rolling off’ the airbag due
to the force of deployment directly onto the driver door frame or A-pillar. This
occupant kinematic scenario has been observed anecdotally in EuroNCAP crash-test
films.
As a whole, the study presented here has proved inconclusive regarding the risk of
head injury through airbag deployment. Whilst laboratory studies have shown that the
injury risk to the smaller stature driver as represented by the 5th percentile female
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hybrid III crash-dummy is not greatly enhanced in a typical 30mph full frontal crash,
it would be useful to consider whether the dummy outcome is similar when the crashpulse is more demanding since accident studies do not provide all of the answers. As
such, it is necessary to examine injury measurements as recorded by the 5th percentile
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female Hybrid III dummies in both higher speed tests and a more rigorous condition
such as the 64km/h 40% overlap offset condition (such as the EuroNCAP test
condition). Even then though, the real-life injury risk to is not always predictable whilst such tests may partially reveal any increased probability of leg injury through
tibial index measurement, lack of wholly suitable biofidelic foot/ankle measurement
apparatus is a drawback.
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REFERENCES
Crandall, J R; Martin, P G; Bass, C R; Pilkey, W D; Dischinger, P C; Burgess,
A R; O’Quinn, T Dschmidhauser, C B. Foot and Ankle Injury; The Roles of
Driver Anthropometry, Footwear and Pedal Controls. Proceedings of the 40th
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Conference of the AAAM, Vancouver, Canada, October (1996)
Dischinger, P; Cushing, B and Kerns, T. Lower Extremity Fractures in Motor
Vehicle Collisions – Influence of Direction of Impact and Seat Belt Use.
Proceedings of the 36th AAAM Conference, Illinois, US (1992)
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Evans, L and Frick, M C; Seating position in Cars and Fatality Risk. American
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Evans, L. Traffic Safety and the Driver. ISBN 0-442-00163-0 Published by Van
Nostrand Reinhold, New York, US (1991)
Kirk, A., Frampton, R., and Thomas, P., An evaluation of airbag
benefits/disbenefits in European vehicles – A combined statistical and case
study approach. Proceedings of IRCOBI Conference on the Biomechanics of
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Lenard, J and Welsh, R. A comparison of injury risk and pattern of injury
between male and female occupants of modern European passenger cars.
Proceedings of IRCOBI Conference on the Biomechanics of Injury, Isle of Man
(UK) October 2001.
Parkin, S; Mackay GM and Cooper A. How Drivers Sit in Cars. Proceedings of
the 37th AAAM Conference, San Antonio, Texas, USA (1993)
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Pheasant, S; Anthropometrics – An Introduction. ISBN 0 580 18234 7
Published by BSI, Milton Keynes, UK. (1990)
Stone, D L. Patterns of Gender Differences in Highway Safety. University of
Wisconsin. (1996)
Taylor, A; Morris, A P; Thomas, P and Wallace, WA
Mechanisms of Lower Extremity Injuries to Front Seat Car Occupants – An Indepth Analysis
Proc. IRCOBI Conference, pp 53-72, Hannover Germany 1997
Wellbourne, E
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Performance
Proc. IRCOBI Conference, pp 151-162, Lyon, France, 1994
http://www.nhtsa.dot.gov/airbags/HwySafety/
T
T
National Highway Transport Safety Administration, Washington DC, USA
http://www.euroncap.com/
T
T
European New Car Assessment Programme (EuroNCAP)
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ACKNOWLEDGEMENTS
This paper uses accident data from the United Kingdom Co-operative Crash
Injury Study.CCIS is managed by TRL Limited, on behalf of the Department for
Transport (Vehicle Standards and Engineering Division) who fund the project
with Autoliv, Daimler Chrysler, Ford Motor Company, LAB, Nissan Motor
Company, Toyota Motor Europe, and Visteon.
The data were collected by teams from the Birmingham Automotive Safety
Centre of the University of Birmingham; the Vehicle Safety Research Centre of
Loughborough University; and the Vehicle Inspectorate Executive Agency of
the DfT.
Further information on CCIS can be found at http://www.ukccis.org
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