EFFECTIVENESS OF CHILD RESTRAINTS

EFFECTIVENESS OF CHILD RESTRAINTS
EFFECTIVENESS OF CHILD RESTRAINTS
THE AUSTRALIAN EXPERIENCE
RESEARCH REPORT RR 06/02
Prepared by
Julie Brown, Michael Griffiths and Michael Paine
for
Australian New Car Assessment Program
June 2002
CONTENTS
INTRODUCTION ..................................................................................................4
International developments............................................................................4
CRS effectiveness .........................................................................................5
HISTORY OF DEVELOPMENT OF CHILD RESTRAINTS IN AUSTRALIA .........5
The Australian Standard for Child Restraints ....................................................6
Top tether strap .............................................................................................7
Six point harness with double crotch straps...................................................7
Single point of adjustment of the harness......................................................8
Rear seat mounting .......................................................................................8
International Standards - ISOFIX ......................................................................8
Suggested improvements to the Australian Standard .....................................10
THE KINETICS OF CHILD RESTRAINTS..........................................................11
The spring-mass system and effects of slack..................................................11
Laboratory Evaluations of top tether performance...........................................13
Laboratory Investigations of child restraint design .......................................16
Other laboratory research ...............................................................................17
Computer Modelling ........................................................................................18
Crash Barrier Tests .........................................................................................18
Simulations of real world crashes....................................................................21
Standards and consumer programs ................................................................21
Child Restraint Evaluation Program (CREP) ...................................................21
Australian NCAP .............................................................................................25
Key Findings from Laboratory Research .........................................................26
Concerns about EuroNCAP Assessment Protocol ..........................................26
STUDIES OF THE EFFECTIVENESS OF CRS .................................................31
Overall estimates of effectiveness...................................................................31
Effectiveness of different types of child restraint .............................................34
Influence of seating position on CRS effectiveness.........................................35
Crash characteristics and the effectiveness of CRS........................................36
STUDIES OF REAL WORLD CRASHES............................................................37
Injuries to restrained children ..........................................................................38
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Injury sources for restrained children...........................................................41
Survival of children in severe crashes .............................................................43
Misuse of CRS ................................................................................................44
Misuse of CRS in Australia ..........................................................................44
Consequences of misuse ............................................................................45
VEHICLES FACTORS AFFECTING CRS PERFORMANCE..............................47
Anchorage systems .........................................................................................47
Method of attachment to ISOFIX anchorages..............................................48
Anchorage geometry ...................................................................................49
Seat belt characteristics ..................................................................................49
Vehicle seat characteristics.............................................................................50
Child restraint interaction with airbags.............................................................51
SUMMARY OF ISSUES......................................................................................52
Australian experience with CRS ......................................................................52
The Kinetics of CRS ........................................................................................53
Effectiveness of CRS ......................................................................................53
Injury studies ...................................................................................................54
Vehicle Factors ...............................................................................................55
CONCLUSIONS..................................................................................................56
Lessons learnt .................................................................................................57
Still room for improvement...............................................................................57
ACKNOWLEDGMENTS .....................................................................................58
REFERENCES ...................................................................................................59
APPENDIX - Assessment of Child Restraint Installation and Use ........................1
1. Introduction ...................................................................................................1
2. Test equipment..............................................................................................1
3. Preparation of vehicle....................................................................................2
Front Seats ....................................................................................................2
Rear seats .....................................................................................................2
4. Installation of child restraint in vehicle ...........................................................2
4.1 Installation instructions ............................................................................2
4.2 Installing child restraint ............................................................................2
4.3 Measuring slack.......................................................................................7
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5. Child Restraint Use - Checks with dummy in child restraint ..........................7
5.1 Preparation of child restraint ....................................................................7
5.2 Placing dummy in restraint.......................................................................8
5.3 Checking clearance within vehicle .........................................................10
5.4 Removing dummy from child restraint ...................................................11
6. Maintenance of child restraint .....................................................................12
7. Calculation of score.....................................................................................12
Disclaimer
The views expressed in this report are those of the authors and do not
necessarily represent the views of ANCAP or any other organisation.
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 3
INTRODUCTION
Australia has several decades of experience in the development of child restraint
system (CRS). During this time the requirements for child restraints, as set out in
Australian Standard 1754, have evolved to incorporate the best features
identified from road safety research and to eliminate undesirable characteristics.
The most significant development was the introduction of the top tether. The
effectiveness of the top tether has been demonstrated in the laboratory and in
the real world crashes in Australia. Canada, the USA and recently France have
recognised the advantages of the top tethers. Top tether anchorages are now
required in North American cars.
International developments
As part of its consumer crash test program, EuroNCAP proposes to introduce
performance criteria for child restraints based primarily on child dummy injury
measurements. However, Australian crash test experience suggests that forward
facing child restraints with top tethers and harnesses will have great difficulty
obtaining better than 'poor' scores under the proposed Euro NCAP assessment
protocol. In the real world Australian child restraints perform extremely well.
There is serious concern that, to achieve reasonable results based on the
dummy injury performance criteria proposed by EuroNCAP test, there is potential
that the level of protection be offered by Australian child restraints will be
reduced. Specifically, laboratory experience suggests that to achieve good Euro
NCAP results would mean allowing greater excursion of the child dummy, with
consequent increased risk of head contact and serious injury. This would be a
retrograde step in Australia.
International endeavours towards harmonisation in the vehicle safety arena can
sometimes cause conflict between having universally acceptable test or
performance standards and avoiding a reduction in the overall level of protection
provided by of a system that has been demonstrated to be performing very well.
This is particularly the case with child restraints, where the level of protection
provided by Australian restraints is arguably among the best in the world.
Since international harmonisation is currently a priority area in the vehicle safety
field it is timely that a review of the Australian experience with child restraints be
conducted. In addition, greater attention is currently being given to the safe
transport of children in the USA with much debate in that country concerning the
potential benefits or otherwise alternative anchorage systems including top
tethers.
This document has therefore been prepared to present the Australian experience
with child restraints in terms of design, both of restraint systems and methods of
anchorage to the vehicle.
Included in this document is a discussion of the development of child restraint
systems in Australia, research that has supported this ongoing evolution and
issues and related findings of studies investigating the effectiveness of child
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restraints in Australia and elsewhere in the world. Issues related to directions in
testing, performance assessment and anchorage methods in other countries are
also given special attention.
CRS effectiveness
Overall effectiveness, in particular comparisons between "effectiveness" of
Australian restraints and restraint systems in other countries is a fundamental
concern when discussing differences in design and assessment . However, in
any discussion it must be remembered that irrespective of fundamental design
differences in child restraints between Australia and elsewhere, it is evident that
child restraints are highly effective devices when compared with adult seat belts.
Certain child restraint designs will be of greater benefit in some situations
whereas the reverse might hold in other crash situations. Effectiveness therefore
has to be considered very carefully to avoid invalid lines of logic.
Likewise, overall estimates of effectiveness are important as general indicators of
the potential injury reduction benefits provided by restraint systems, but it is also
important to consider the potential influence of other factors such as crash type,
seating position and correct use.
The effectiveness of Australian child restraints compared with other countries is
of great interest to any discussion where the benefits of one type of system are to
be weighed against another system. But there are a number of limitations in
using available Australian data in direct comparisons with estimates reported
overseas. This document therefore goes into some detail regarding these
limitations and the types of studies necessary to make meaningful comparisons.
HISTORY OF DEVELOPMENT OF CHILD RESTRAINTS IN
AUSTRALIA
Australian research on child restraints started in the late 1960s through
organisations such as the Traffic Accident Research Unit of New South Wales
(TARU). This early work recognised the benefits of children being restrained in
the rear seat and "riding down" the crash with the vehicle (Herbert and others
1974).
Australian Standard AS E46 for child restraints was issued in 1970. It required at
least three points of attachment between the CRS and the vehicle. Most CRS
utilised either three special attachment straps or a combination of an adult seat
belt and a top tether to achieve this requirement. However, some designs relied
solely on a three point adult seat belt. From the start there were concerns about
this arrangement but imminent introduction of retracting inertia reel seat belts for
rear seats of cars in the mid-1970s was a factor in a major review of the
standard. AS1754-1975 required dynamic tests for the first time and led to
greater (although not universal) use of a top tether on CRS sold in Australia. This
was aided, in 1976, by an Australian Design Rule (then ADR34) that required
standardised top tether anchorage points to be provided on the parcel shelf of all
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 5
sedans. Australia has therefore had more than 25 years of experience with top
tethers on CRS.
The performance of CRS in real world crashes has always been closely
monitored in Australia and has been complemented by laboratory research using
sleds, crash barriers and computer modelling. In the light of this experience the
Australian Standard has evolved to eliminate shortcomings (in some cases
demonstrated by poor performance in the real world) and to incorporate best
practice. In "Crash Protection for Child Passengers: A Review of Best Practice",
US child restraint expert Kathleen Webber reports favourably on the
configuration of child restraint used in Australia and states "all CRS work on the
principle of coupling the child as tightly as possible to the vehicle" (Webber
2000).
The Australian Standard for Child Restraints
All CRS sold in Australia must comply with Australian Standard 1754. This
standard sets outs requirements for the design of child restraints, such as easeof-use, and dynamic performance.
During the 1980s the New South Wales
Government set up a network of child restraint
fitting stations to improve the quality of
installation of CRS, including retrofitting top tether
anchorages. From this network road safety
researchers gained invaluable first-hand
knowledge of the kinds of problems that people
encountered using child restraints. They then
developed solutions to those problems, and
identified areas where improvements in the
Standard were required.
This was important, because it meant that when
issues were brought to the Standards
Committee’s notice, the road safety authorities
were able to provide good advice based on firsthand experience, and to make specific
suggestions for any improvements or changes
required. Rarely is such expert, "hands on"
experience available for the purpose of
developing standards.
Figure 1. Features of Australian CRS
The combination of a standard for CRS and an
Australian Design Rule for CRS anchorages in vehicles has some significant
outcomes which set them apart from other standards in North America and
Europe. These include (see Figure 1):
1) mandatory top tether strap
2) single point of adjustment of the harness
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3) six point harness with double crotch straps
4) rear seat mounting is normal practice
5) careful specification of the location of mounting points for top tether straps in
vehicles (to assist accessibility and optimise performance)
6) a specially developed infant dummy, much more flexible than overseas infant
dummies (hence more prone to ejection)
Some of these features are discussed in more detail below.
Top tether strap
Top tethers provide much more secure attachment of child restraints compared
to being attached by the seat belt only. In particular, they provide more rigid
attachment at the top part of the child restraint, so that it can “ride down” the
crash whilst the vehicle is crushing. This considerably reduces excursion of the
child's head relative to the vehicle interior so the head is far less likely to hit other
parts of the vehicle interior - the most likely cause of serious injury to a properly
restrained child.
A further advantage of top tethers is that they allow good, reliable performance
with a lap-only adult seat belt. Therefore the centre rear seating position, which
usually has a lap belt, can always be utilised (in NSW 40% of forward facing child
seats are installed in the centre rear seat).
Six point harness with double crotch straps
It is evident that both harness and shield styles of CRS are capable of performing
exceptionally well but each style also has inferior designs.
During the review of the Australian Standard in the early 1970s shield style CRS
were considered as an alternative to the use of a harness. However, dynamic
tests of shield style CRS that were sold widely outside Australia revealed
structural deficiencies and a risk of ejection. There were also concerns about the
application of force to the abdomen rather than the chest and pelvis that are
better able to cope with crash forces. For these reasons the performance
requirements of the revised standard discouraged shield style CRS and they
have never been used in Australia.
Overseas there remain mixed views on the performance of shields. Webber
(2000) reports on serious deficiencies with both "tray shield" and "T shield" CRS,
common in the USA, and better relative performance of harness restraint. On the
other hand, Hummel and others (1993) concluded from German study that "there
is a significant higher tendency to severe injuries where 4/5 point (harness)
systems are used". However, in the German study the sample sizes were small,
the shield systems may have been a more effective design than those in the
USA, the harness cases may have included the inferior four point systems and
none of the CRS had top tethers. It therefore does not apply to Australian CRS.
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In Australia early experience with four point harnesses proved to be very
unsatisfactory with a high risk of the child submarining and being exposed to
either ejection, dangerous loading of the abdomen or strangulation. Unfortunately
there were also cases of children dying in stationary vehicles when they slipped
down and were caught by the neck. Single crotch straps reduced the risk of
submarining and were required under the standard.
Double crotch straps were initially introduced because of a fear (not
substantiated by any actual incidents) of causing damage to the child’s
reproductive organs. A considerable amount of research was conducted into
trying to find a repeatable standards test to measure the pressure applied by
child restraints to that part of a child’s anatomy, however no reliable method was
ever identified. Ultimately, after more than five years of research, the Australian
Standards Committee decided to simply mandate the design feature of twin
crotch straps, rather than try to find a way of assessing the performance of single
crotch straps. Subsequently all child restraints made and imported into Australia
have been successfully designed or adapted to incorporate dual crotch straps.
Single point of adjustment of the harness
Early model child restraints had adjusters on many of the harness straps. Road
safety researchers found that the more adjusters in a child harness there were,
the more potential there was for incorrect or slack adjustment. The decision was
made to mandate a design feature of a single harness adjuster only, so as to
reduce the potential for loose fitting harnesses. Some single point adjusters were
initially awkward, however development has now seen adjusters become a lot
easier.
Rear seat mounting
There has been considerable publicity relating to the problems of airbags
interacting with child seats installed in the front seat. This has been a major issue
in Europe and North America.
Because all Australian CRS must have a top tether and the anchorages for top
tethers are exclusively located in the rear of Australian cars, Australia parents
have developed the habit of always restraining young children in the rear seat. In
fact most of the current generation of Australian parents were, as children,
restrained in the rear in similar CRS to those used today.
The exclusive use of rear seats means Australia has not encountered any of the
problems due to the interaction of CRS with front airbags and there is no need to
disable front passenger airbags in Australia.
International Standards - ISOFIX
Australia has had ongoing involvement in the International Standards
Organisation Committee developing a new Standard for child restraint systems
(ISO-CRS) since its earliest meeting in the mid 1980s. At that time it was
recognised that child restraints needed to be more firmly attached in cars and
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 8
there was a need for separate attachment systems for child restraints that did not
rely on adult seat belts.
The UK representative, Richard Lowne, presented to the committee the results
of an evaluation of all possible methods of attachment of child restraints and
concluded that the most effective and easily implemented system would be one
which had the child restraint attached at two points at the base and a single top
tether. Opposition to top tethers, however, was so strong in some parts of Europe
that this concept was abandoned and the system proposed was a four point
attachment system, with attachments at each of the four corners of the base of
the child restraint, with no upper restraint.
Ten years of development of such a system was undertaken, and it was close to
implementation when the U.S. automotive manufacturer, General Motors did its
own evaluation and concluded that top tethers could offer most, if not all, of the
benefits of a four point rigid base system at a fraction of the cost.
This brought about an impasse position on the ISO Committee and stalled
progress. Fortunately at that stage the U.S. Government intervened and a
special U.S. 'Blue Ribbon' taskforce was set up to look at how better restraint
systems could be offered to North American children. An outcome of that review
was the LATCH system and a requirement for top tether anchorages in cars and
effectively set development of child restraints in North America to those with top
tethers (Webber 2000).
This then gave the option of child restraints being attached by a top tether and
two lower anchorage points. This caused a review of the ISOFIX so that vehicle
seats intended for use with CRS must be provided with two rigid lower
anchorages and "a means to limit the pitch rotation of the CRS". In almost all
countries the latter requirement will be achieved with a top tether. Remaining
opposition to top tethers by some European researchers, and the ongoing
disinterest in Sweden (which has unique CRS provisions), is unfortunate but has
no significant effect of the global adoption of top tethers.
The provision of top tether anchorages is not an issue with most European,
Japanese and Korean manufacturers - all imported vehicles in Australia have the
fixings in place. Indeed, many manufacturers include the top-tether anchor/weld
nuts on all models in non-Australian markets to reduce manufacturing
complexity.
Vehicles with ISOFIX anchorages are now on the market. The Australian CRS
standard is being reviewed to encourage designs that take advantage of the
potentially improved lower restraint provided by ISOFIX, compared with adult
seat belts. It is expected that this will improve the performance of Australian CRS
in side impact crashes and will also eliminate the main form of misuse in
Australia - incorrect use of the adult seat belt for securing the CRS (discussed
later).
On the other hand, the lack of ISOFIX lower anchorages for the centre rear
seating position will probably reduce the use of this desirable seating position by
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 9
children in CRS. Although, under the proposed Australian Standard, the CRS
must be able to be used in vehicle with and without ISOFIX it is likely that parents
will use outboard seating positions that have ISOFIX anchorages in preference to
the centre seat that only has a seat belt.
Suggested improvements to the Australian Standard
Despite their proven effectiveness in many types of crashes there are still
improvements that can be made to Australian child restraints. For example:
•
Boosters with better sides for the sleeping child – these are to allow a child to
sleep, which they so often seem to like to do in travelling cars. The sides
ensure that the sleeping child doesn’t fall out of the booster, and keep the
child’s torso in position, so that the restraint system and seat can offer
protection in the event of a crash.
•
Further development or addition of energy-absorbing side wings to all child
restraints to protect the head in the event of a side impact. This will also
require that the child restraint is secured to the vehicle in a way that the side
wing remains interposed between the child’s head and the side of the car in
the event of a side impact (a situation that could potentially be improved
through use of ISOFIX lower anchorages - see next item).
•
Tight fitting of the base of the child restraint to the car seat, either through
tensioned rear base straps or rigid base fittings. ISOFIX type fittings should
enable this to be readily achieved. Firm lower mountings, in conjunction with
a tightly fitted top tether strap, should maintain child restraint position so that
(amongst other things) side wings can stay between a child’s head and the
car interior.
•
Visual indicator systems which indicate when the child restraint is correctly
fitted and all the straps are tensioned correctly. Such systems could be
mechanical or electronic.
•
Tighter restrictions on (regulated) zones for location of top tether anchorages
for child restraints. If anchorages are too far away from the back of the seat
they can be both difficult to locate and difficult to attach a strap to. The
Australian experience has been that the larger the zone, the more problems.
Although this has already been addressed to some degree through the
Australian Design Rule system, there is still scope for improvement.
Countries considering regulating the location of top tether anchorages should
note that many vehicle models sold in North America and Europe are also
available in Australia where, for many years, manufacturers have provided
anchorages that meet stringent Australian requirements.
•
More biofidelic child test dummies and validated injury criteria. Early child test
dummies were quite crude and basically designed to assess the strength of
the CRS and its ability to restraint the occupant. New test dummies that do
have better (but not optimal) biofidelity are available but considerable
research is still needed for the setting of injury criteria, for use with these
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 10
dummies. In particular it would be inadvisable to base a CRS standard or
consumer rating system primarily on dummy injury measurements.
•
Australian children are often turned around to forward facing at 5 to 6 months
of age. Europeans and North Americans think this is much too early, and that
they will be vulnerable to spinal injury at that stage. The Australian
experience indicates that these concerns are unfounded, although it is readily
agreed that in general it is preferable that a child remains rearward facing for
as long as possible.
•
Improved protection for the 3-10 year olds. Real world studies have shown
children correctly restrained in dedicated infant and child restraint systems
with in built harness systems are generally more protected in crash situations
than children in other types of restraints and adults in adult seat belts.
Children moving out of this restraint too early and even children too big for the
type of restraint often move directly into adult belts or adult belt and booster
combinations. There is scope for improving the level of protection available to
those children through improved booster design (and use).
THE KINETICS OF CHILD RESTRAINTS
Australian practice is to have a firm attachment between the CRS and the vehicle
and to have the child firmly restrained by a harness - the intention is that the child
"rides down" the crash with the vehicle. There are sound physical principles
behind this approach.
The following analysis illustrates this principle and also points out the
consequences of having slack in the system. It is important that slack be
considered when assessing potential injury mechanisms in real world crashes.
The spring-mass system and effects of slack
Consider the over-simplified system of a heavy ball attached to a spring. The ball
represents a child and the spring represents the combined elasticity in the CRS,
arising from stretch of straps and bending of components. See figure 1, overleaf.
For a system with no initial slack the ball is supported (equivalent to having no
acceleration acting on the ball) as shown in diagram A and there is no tension or
compression acting in the spring. When the support is taken away the ball will fall
until the force in the spring increases sufficiently to stop its motion (B). The ball
will then rebound (assuming a perfectly elastic system) and eventually settle at
an equilibrium position (C). At this point the force in the spring will be equal to the
mass of the ball times the acceleration due to gravity. In this case the equilibrium
point is halfway between the position of the ball in diagrams A and B. Since the
spring force is proportional to the distance of extension then the force at point B
is twice that of point C. In other words, with an undamped spring mass system
the peak acceleration acting on the sprung mass will be twice the acceleration of
the frame of reference. Importantly, this outcome is independent of the spring
rate.
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With a real child restraint
system, the harness and other
components absorb some of
the energy and reduce the
peak acceleration acting on the
child, but the principles are the
same.
Now consider the introduction
of slack into the system (D). In
this case the ball will free-fall
(accelerate under gravity) until
the slack is taken up (E). At this
point its velocity will be:
Figure 2. Simplified spring mass system
where v is relative velocity, a is the acceleration of the frame of reference and s
is the amount of slack.
For example, if a = 30g (294m/s2) and the slack s = 100mm (0.1m) then the
relative velocity v = 7.7m/s. The ball has acquired kinetic energy before the
spring starts to extend. This extra energy must be absorbed by the spring, which
extends further in order to arrest the motion of the ball (the extension is
proportional to the square root of the energy). This means that additional force is
applied through the spring and consequently the peak acceleration of the ball is
greater.
For a hypothetical case where the mass of the child is 20kg, the spring rate of the
CRS is 30kN/m (or a 6.5mm extension under the force of gravity) and the car
body is decelerating at 30g the theoretical peak acceleration of the child is 60g
with no slack and 73g with 100mm of slack. This is illustrated below.
Figure 3. Effect of slack in an elastic restraint system
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 12
The extra extension of the "spring" (80mm for the above case) needed to absorb
the additional kinetic energy is added to the initial slack in the system (100mm) to
produce a large overall excursion (180mm) of the occupant - with consequent
increased risk of head contacts. This extra excursion could be a greater hazard
than the increased acceleration resulting from slack in the system.
It is evident from this analysis that any "give" in the restraint system is only useful
if it absorbs and disperses the energy of the moving occupant. Displacement due
to slack or elastic spring extension will not absorb this energy and could increase
the risk of injury. In particular, softly sprung systems that do not effectively
absorb energy will not reduce the peak acceleration forces on the occupant but
instead will allow greater excursion of the occupant before the peak forces are
reached.
Many modern adult seat belt systems have pre-tensioners to remove initial slack.
This is in agreement with the principles of restraint of children.
Some adult seat belts also have load-limiters that allow extra extension of the
webbing but this is usually a deformation action that absorbs energy. If the loads
being applied to children by firmly attached CRS were proving to be too high and
causing serious injury then it would be appropriate to consider some form of
energy-absorbing load limiter in the CRS or harness webbing. However, as
discussed later, this has been found to be unnecessary in Australia, even in high
speed impacts.
Laboratory Evaluations of top tether performance
The issues under discussion in international task forces, such as ISOFIX, raised
a great deal of interest in the potential benefits or otherwise of anchorage
systems that incorporated top tethers. One of the most frequently posed potential
dis-benefits of such systems had long been related to a theoretical potential for
increased neck injury risk. Such a concern arises due to the real anatomical
differences that exist between adult and children such as the greater relative
mass of a child’s head relative to its torso than an adults and a child’s relative
weaker neck musculature. Concerns based on these differences basically fall
into two main groups. Those that are associated with the fear that by tying a
forward facing child’s torso rigidly to the vehicle, the neck may be at risk in frontal
impacts through flexion (bending forward); and, those associated with allowing
the neck to be loaded (via inertia) by the mass of the head.
Worldwide concern regarding the increased risk of neck injury in children
restrained in forward facing restraints grew throughout the late 1980's. This was
largely due to a small number of cases of severe neck injury in restrained
children reported in North America and Europe. Significantly no such cases have
ever been reported in Australia.
Detailed study of these case reports by an International Task Force found that all
European cases involved seats incorporating 4 point harness and the North
American cases involved one restraint with a 5 point harness and another with a
harness/shield system. None of the restraints used a top tether.
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 13
In addition at least half of the cases were judged to have likely involved head
contact (Tarriere and others, 1991). Australian experience is that the child's neck
is quite resilient when subject to pure tension but is extremely vulnerable to
moderate lateral loading when under tension. One of the difficulties with crash
investigations involving neck injury is establishing whether a head contact did
occur, since even a mild head contact can cause neck injury under some
circumstances. Great caution is therefore required in the evaluation of cases
involving neck injury.
The influence of anchorage systems on forward facing child restraint
performance became a primary study target for researchers trying to understand
why these types of injuries had occurred.
One of the first such studies, conducted by the international Task Force looking
at the problem found that neck forces and movements were significantly lower in
a 3 year old dummy in a tethered restraint compared to a non tethered restraint
(Brun Cassai and others 1993).
In contract to this, Janssen and others (1993) reported that in their comparison of
tethered and untethered restraint, the presence of top tether slightly increased
the neck loads produced in their test dummy, however this dummy was of a
completely different design to that used in the above study.
A similiarly designed dummy as that used by Brun Cassan and others (1993)
was used by Weber and others (1993) in a similar comparison, but Weber and
others also reported little beneficial effect on neck loads by the inclusion of a top
tether.
An Australian study (Brown and others, 1995) also comparing the performance of
tethered restraints found that the presence of a top tether can significantly
improve the protection offered by forward facing seats. However this work noted
that the benefit from top tether use was not as significant for all models of
forward facing child restraints. Brown and others (1995) observed that geometry
of the tether anchorage or the position of the tether mount on the child restraint
appeared to have some influence on how much the tether affected the
performance of the restraint (when performance is assessed by loads felt on the
dummy). This issue was also investigated by Legault and others in 1997. These
authors also reported that the presence of a top tether improved the performance
of the forward facing restraints. However they believe that although there may be
some difference in performance depending on the position of top tether mount,
the improved performance introduced by the top tether on any restraint means
that the presence of the tether strap is relatively more important than the location
of its mounting point.
In this respect, Legault and others (1997) are referring to the major benefit of the
top tether in frontal impact -the influence on reducing head excursion. This
finding was also highlighted by the Brown and others study (1995).
Since the major reason for many of the top tether studies conducted through out
the 1990’s was as a response to the reported neck injury in North America and
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 14
Europe, most work was conducted using frontal impact only. The influence of top
tethers on child restraint performance in side impact came under scrutiny in the
latter part of the 1990’s in response to the international debate regarding
universal anchorage methods.
Australian researchers, confident of the benefits of anchorage systems
incorporating top tether system from real world experience (and laboratory
studies such as those cited above) were keen for a universal method that
continued to utilise a top tether arrangement. Laboratory work in Australia had
shown that this method of anchorage also limited sideways movement of forward
facing child restraints in side impact. Kelly and others (1995) reported that the
lack of top tether reduced the protection potential of forward facing restraints in
both 45º and 90º side impacts, however it was noted that the extent to which the
tether influenced the sideways movement was different for different designs of
restraint. In rearward facing restraints, the top tether had the greatest influence in
minimising unwanted sideways movement of the restraint in side impact.
However the degree of beneficial influence of the top tether in side impact was
noted to be less then that observed in frontal impact. In fact, the lateral stability of
the child restraints in side impacts appears to be more influenced by the
geometry and rigidity of the lower anchorages (rather than the top tether).
Australian researchers therefore considered that the area where the greatest
gains could be achieved in side impact protection was by improving the two lower
anchorages.
With respect to the universal anchorage method debate, the Australian position
has been that the performance of the current Australian anchorage system,
consisting of adult belt and mandatory top tether, works extremely well in frontal
crashes. This position was based on laboratory studies such as those discussed
above and field studies. However, Australian road safety professionals believed
(and still do) that this form of anchorage is less than optimal in side impacts
(Brown and others 1997). Almost all Australian child restraints (and probably
restraints available elsewhere) when used in conjunction with adult seat belts
allow some degree of undesirable sideways motion in side impact.
Further Child Restraint Laboratory Work In Australia
Australia has a long history of crash barrier and sled testing of child restraints.
This research has been performed primarily to assist in the development of the
Australian or international standards and to better understand the mechanisms of
injury (or survival) in real world crashes. More recently a consumer evaluation
program for child restraints was introduced.
This section contains a review of the Australian research. Some of the research
has not been formally published before but nevertheless made an important
contribution to the development of current Australian and international standards.
As discussed previously, some of the most important laboratory work carried out
in Australia in recent times concerned the influence of top tethers. This work,
together with the anchorage method studies, formed the basis for a series of
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 15
experimental work carried out in Australia throughout the late 1990s and recent
years.
Laboratory investigations of child restraint design
With respect to child restraint design, the top tether work reported by Brown and
others (1995) and Kelly and others (1995) and cited above, highlighted
differences in performance between restraints of different design. This
observation had also been made anecdotally during earlier routine child restraint
standards testing and led to the development of the Child Restraint Evaluation
Program (CREP) program. Although Brown and others (1994) found some
performance differences due to the influence of top tether mounting positions,
Australian researchers knew that other design variables theoretically also had the
potential to significantly affect the level of protection, in particular the amount of
head excursion. One of the first variables examined (after the top tether work)
was the influence of harness mounting height.
A range of harness adjustment heights is necessary to ensure a good fit for
children across the whole design range for any specific type of dedicated child
restraint. For example Australian forward facing child restraints are classed as
‘Type B’ restraints by the Australian Standard and are required as part of this
classification to be designed to carry children from 9kg to 18kg. A laboratory
study was conducted in the 1990s to explore the relationship between harness
shoulder strap position and dummy shoulder position. This work found that
harness straps positioned below a dummy's shoulder causes small decreases in
head and neck loads, but significant increases in lumbar loads. Shoulder straps
positioned above the shoulder were found to reduce head excursion, allow small
increases in peak head acceleration and neck forces but have no effect on
lumbar loads (Sampson and others 1994).
The complexity of such influences, when reviewed together with that of top tether
mounting height, led researchers at the NSW Roads and Traffic Authority (RTA)
to realise that attempting to study each design variable and analysis the parallel
influences of each variable using simulated impacts was likely to be a long and
costly exercise. Working with the University of Sydney, the RTA designed a
program to study these types of variables using mathematical modelling. This
research program produced some interesting, but as yet unpublished,
information.
In summary, this work ratified the finds of Sampson and others (1995) and Brown
and others (1995), and then went further to study design variables such as
harness webbing properties, lap belt geometry, top tether length and child
restraint seat back angles (Lixang, unpublished). Preliminary findings are ;
(i)
of the investigated parameters, design variables such as seat back angle
and lap belt position (or the geometry of the bottom anchorage) are the
variable most likely to have the greatest potential to influence child
restraint performance, and
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 16
(ii)
all of the design variables investigated (ie seat back angle, top tether
length, top tether mounting height, lap belt geometry) have optimal values.
In other words, the level of protection afforded by a child restraint will vary
within a defined range of design characteristics and at some point in this
range lies an optimal design specification.
Other laboratory research
Australian researchers, based on field and laboratory studies like those
discussed above, have long been reporting the good performance of child
restraints in frontal impact. In side impact, from field experience in particular, it
has been evident that the protection of child restraints can be improved
significantly by design and anchorage modifications enhancing side impact
performance. Results from field studies discussed later in this document highlight
this issue in greater detail. Researchers from the NSW RTA have reported on
numerous occasions (Brown and others, 1997) that the three main goals of a
child restraint system in side impact should be;
(i)
ensuring that the child restraint has ‘sidewings’ that retain the head
(ii)
once the head is retained, providing some form of energy absorption in the
‘sidewings’
(iii)
preventing excessive sideways movement and rotation of the child
restraint.
Some, but by no means all, Australian rearward facing and forward facing child
restraints already provide relatively effective side structures (or sidewings) that
work to retain a child’s head in side impact. Very few of these provide some
means of energy absorption in the side structure to protect the head from side
impacts. An unpublished series of laboratory simulated impacts conducted at
NSW’s Crashlab in the late 1990s demonstrated that a relatively minor
modification aimed at providing energy absorption could greatly improve the
potential head protection provided by a popular Australian forward facing
restraint. This model of restraint already has well designed side wings that have
been shown to satisfactorily retain a dummy’s head in most side impact
orientations. The energy absorbing characteristics of the side wings were altered
by have polystyrene beads poured into the existing gap between the outer and
inner surface of the sidewings. The beads were treated in the same manner as
that in the manufacture of foam liners for pedal cycle and motor cycle helmets.
The result was a significant drop in the head loads measured in child dummies
during 90 degree side impacts. This modification was tested with two different
types of dummy, and in simulated sled impacts and car to car tests. The side
impact protection of the device was found to be improved in all test types.
With respect to limiting sideways movement of restraints in side impact,
Australian laboratory work (both on the sled and barrier tests) have demonstrated
that an ISOFIX approach,(ie two rigid anchorages at the base of the restraint and
a top tether) can significantly limit sideways excursion. (Kelly and others, 1995,
Brown and others 1997, NSW RTA Crashlab unpublished work)
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 17
Finally the restraint of children in adult restraint systems has also been the
subject of laboratory research in Australia. Henderson and others (1997)
reported on a sled test series investigating the level of protection provided to a
range of child dummies by adult belt systems. This work demonstrated that lap
only belts and lap/sash belts potentially do provide some level of protection, for
even the very young child (approximately 2 years). However the protection
provided by lap/sash belts is far superior to that of lap only belts, and for the very
young child a child restraint is the optimal form of restraint. As is discussed in
later sections of this report, these findings basically mimic in a laboratory setting
was has been observed in field studies.
Computer Modelling
Modelling work described above was achieved using a mathematical package
employed widely in the vehicle safety and design area - the lumped mass
MADYMO package. Until this work was completed, no MADYMO child dummy
database, that was designed to perform in a human like manner, existed. The
completion of this database, applicable for frontal crashes, has opened the way
for further such complex work in Australia and overseas. Since this database was
completed, a second database for the same child dummy but validated for side
impact has been reported (Roberts and others, 2002). To date no research using
this side impact database has been reported.
Crash Barrier Tests
The NSW RTA Crashlab has conducted a number of unpublished barrier tests
that have included child restraints and instrumented child dummies. The most
notable of these tests was the Variable Speed Test Program. This program
involved a series of crash tests using the same model vehicle at varying impact
velocities. The impacts ranged from 40km/hr to 100km/hr. Adult Hybrid III
dummies occupied the front seating positions in all but the 100km/hr test. Fully
instrumented six month CRABI dummies restrained in forward facing child
restraints were positioned in the left and right rear-seat passenger positions for
each test, including the 100km/h test.
This test program was conducted very soon after the sled work investigating the
influence of top tethers on child restraint performance reported by Brown and
others (1994). Since a major finding of this work was the potential difference in
performance observed due to different tether mounting positions, the forward
facing restraint systems chosen for the variable speed program where models
that represented a ‘high’ and ‘low’ mounted top tether. A number of interesting
observations related to child occupant protection, and tether position specifically
were made from this program.
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 18
With respect to the top tether mounting position issue, the results from this
program confirmed the observations reported by Brown wt al (1994) that the
design of the child restraint can have a potentially significant influence on dummy
response. This held true in each individual test speeds and was also apparent at
increasing test speeds. In particular, the variable speed test program
demonstrated that the difference in the level of protection for the head, chest and
some neck loads become relatively greater at high impact speeds. However for
other neck loads (axial forces, and flexion moments), the influence of restraint
design is less evident with no clear patterns apparent. Overall, the high mount
restraint had the most marked effect on limiting head and chest acceleration. The
high mount system resulted in significantly lower chest loading (approximately
50% less than low mount restraints) and consistently lower head accelerations.
This is an important outcome when considering the results of other laboratory
work, and crash investigations,
involving CRS with top tethers.
The variable speed program
also provided interesting insights
into the effectiveness of adult
protection systems compared to
CRS. There was an obvious
difference in the patterns of
response obtained from the front
seat adult dummies and rear
seated
child
dummies.
Specifically, the adult HIC values
demonstrated an exponential
increase with increasing impact
speed while the child dummy Figure 4. Variable speed crash tests by Crashlab.
values tended to level off at Lower image shows peak of 40km/h crash. Top
speeds over 60km/h. Even in the images shows peak of 100km/h crash, which was
100km/h test the HIC for the considered to be survivable for the child dummies in
CRS installed in the rear seat.
child
dummies
was
not
significantly greater than those
at lower speeds. However there were no results available for the adult dummies
in the 100km/h test. There was a steady increase in peak chest acceleration in
both front seat passengers. There was a significant difference in the peak chest
accelerations obtained from the two child dummies in the rear seat. One dummy
showed a steady increase while the other increased less rapidly. It is interesting
to note that the head and chest regions of the two front seat adult occupants
gave similar levels of response in each test. However the two child dummies, as
discussed above, often produced differing results particularly in the response of
the head, lower neck axial force and chest. (Brown and others, unpublished RTA
report)
The difference in the pattern of head response observed between the front seat
occupants and rear seat occupants are obviously due to differences in the ride
down effect introduced by the differences in the restraint system, contact with the
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 19
vehicle interior (with gross intrusion into the front occupants survival space at the
higher speeds) and the distance from the front of the vehicle to the occupant (in
effect, the available crush distance).
This different adult restraint system effectiveness, and the level of protection
provided by different seating positions has been reported by statistical
investigations of restraint system effectiveness conducted elsewhere in the world
(discussed in more detail later in this document). However, no such similar
barrier investigation is available in the literature.
Finally, the variable speed test program provided a number of results that raise
serious doubts about proposals to use child injury measurements for assessing
CRS performance. For example, the problem becomes clear if the CRABI six
month neck measurements obtained from this program are compared to neck
injury limits proposed by Mertz and others. (See figure 5).The measured axial
neck loads in both child dummies are significantly greater than the injury
threshold levels proposed by Mertz. This is even the case with the low speed
40km/h test. As discussed later in this document, neck injury (without head
contact) has never been reported or observed in Australian child restraint field
studies even though these studies have included crashes of much greater
severity than the 40km/h barrier test. This raises serious questions about the
proposed neck injury criteria and further work is needed before these criteria can
be confidently used in any assessment of CRS performance.
Figure 5. Upper Neck Maximum Fz compared with AIS 3+ IARV (Mertz)
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 20
Simulations of real world crashes
The NSW RTA has conducted a small number of real world crash
reconstructions, and simulated reported real world problems. None of these have
been formally published. In summary these tests have involved;
(i)
reconstruction of improper use of child restraints observed in the field
including analysis of kinematics and mechanisms of injury
(ii)
reconstruction of impacts involving catastrophic injury to restrained
children. These cases have shown that problems with rear seat design
contributed to injury in the real world
(iii)
investigation of possible sub optimal features of child restraints. Results
from some of these investigations have led to revisions to the Australian
Standard..
Standards and consumer programs
Child restraints used in Australia must comply with AS1754. The dynamic tests
for CRS are set out in AS3629.1. This specifies sled tests for forward facing child
seats (type B restraints) as follows:
•
a frontal impact at about 49km/h with a peak deceleration of 24g and
•
a 90 degree side impact test with a peak deceleration of 14g and an impact
speed of 32km/h.
•
a rear impact test with a peak deceleration of 14g and an impact speed of
32km/h.
•
Inverted test at 16km/h to simulate a rollover crash (rearward facing
restraints).
Systems are assessed for:
•
retention of the CR
•
retention of the dummy
•
separation of load bearing components
•
fragmentation of rigid components
•
adjuster slip
These assessments are made in all test configurations.
Child Restraint Evaluation Program (CREP)
Australia has operated CREP for more than a decade. CRS are subjected to
dynamic tests (some more severe than the Australian Standard) and usability
trials. Consumers are advised of the best performing restraints (via brochures
and the internet).
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 21
It was realised early in the development of CREP that it would not be appropriate
to apply dummy injury performance limits to the ratings due to a lack of biofidelity
of the dummies and uncertainty about the application of dummy injury
measurements to injury risk in children. Dummy injury measurements are
considered during the assessment process but are secondary factors - head
excursion and risk of head contact are considered far more important (Kelly and
others, 1996).
Of particular concern to Australian researchers is that a misguided attempt to
reduce dummy injury measurements could result in greater head excursion and
therefore greatly increased risk of a head contact, resulting in serious head and
neck injury. Real crash experience in Australia, where children have been found
to survive extremely severe crashes without serious injury, calls into question
current injury limits for children, which are mostly based on extrapolation of adult
limits (Brown and others 2001, Trosseille and others 2001, Melvin 1995,
Beusenberg and others 1993).
NHTSA is considering the introduction of a consumer rating program for CRS in
the USA (NHTSA website). Submissions to NHTSA have expressed concern
about the reliance on dummy injury measurements. Australian experience
support such caution: at the current state of dummy development and knowledge
about child injury tolerances, it would be inappropriate, and quite likely counterproductive, to base a CRS consumer rating program primarily on child dummy
injury measurements.
Similar concerns apply to a CRS assessment protocol being developed by the
European New Car Assessment Program (EuroNCAP). Child dummies are
restrained in CRS in the rear seat of vehicles that are crash-tested under the
program. Australian NCAP has found that, in general, Australian CRS do not
meet the unvalidated dummy injury limits proposed by EuroNCAP. Furthermore,
the EuroNCAP protocol explains that the vertical chest acceleration limits are
based on those set out in ECE Regulation 44 for CRS. In effect, the Regulation
limits compression of the spine (a concern with rearward facing restraints) but
without explanation, EuroNCAP applies the limit in both directions. Forward
facing restraints normally load the spine in tension and so the ECE 44 limits are
considered inappropriate.
Australian researchers, consumer organisations and state authorities involved in
ANCAP are concerned that insistence by EuroNCAP on inappropriate injury
limits might encourage CRS that offer inferior real world protection (Paine and
Brown 2001). ANCAP maintains a strong position and input to EuroNCAP
regarding this issue.
CREP Assessments
CREP assessments are based on the Australian Standard but involve higher
crash forces and additional test procedures. In addition to the AS1754 tests an
extra frontal test at 56km/h and 34g is conducted. In addition, the CREP side
impact test, although conducted at the same severity and orientation (90
degrees) as required by AS, includes a structure that is intended to replicate the
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 22
interior of a side door as part of the test configuration. An extra side impact test is
also conducted. This second side impact is conducted at the same severity with
the same test set up but uses an impact angle of 45 degrees.
Forward facing child restraints are assessed
using a P6 dummy for the frontal test and a
P3/4 for the other tests.
The CREP assessment criteria include those
covered under AS1754. The following
measurements are also recorded.
•
Harness strap forces (frontal test)
•
Tether forces, harness forces and seat
belt forces (frontal test)
•
Head acceleration
•
Figure 6. CREP Test at 45 degrees
Head displacement (frontal test) –
including rebound – limits apply to
upward and rearward excursion (during rebound) but not to forward
excursion.
•
Head retention (containment) – side impact tests
•
HIC
•
Retention of device and dummy
•
Adjuster slip
•
Buckle release force (frontal tests)
Note that chest decelerations are measured for infant capsules (Type A) but not
child seats.
For most criteria there are no limits set for performance – the models of restraint
are simply ranked in order of measured values and good performers tend to
stand out in these lists. There are specific reasons for excluding child restraints
from the ’preferred buy’ list. These include;
•
Not passing requirements of Australian Standard in all test configurations
•
Head excursion outside prescribed limits in frontal test or rear impact test
•
Head contact with test rig during side impact test
Ease of use and compatibility issues are also taken into account in deciding
which restraints should be given a ‘preferred buy’.
The procedures used to rank the ease of use, include a judgement regarding
how simple it is to put each restraint into a vehicle, and how easy it is to secure a
child in the restraint. (Kelly and others, 1996).
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 23
Installation judgements in the first CREP series were made in the following
manner:
• A panel of “trialists” were used who had no or limited installation experience
• Trialists installed each model of restraint into a vehicle and an assessor
scored each attempt.
• Scoring was based on
ease of reading and understanding instructions
placing the restraint in the car
routing the seat belt
adjusting and attaching the top tether
Ease of securing the child in the restraint was assessed in the following manner:
• trialists who had no or limited child restraint experience were required to
secure a child into each restraint
• scoring included
ease of reading and using instructions
ease of adjusting harness
ease of putting the child into the restraint and the harness
ease of using a buckle and harness straps or tether (as
appropriate)
ease of releasing the child from the restraint
ease of placing the bassinette in the car (if removable)
(It is assumed that ease of use is still assessed in the same manner since no
detailed report regarding this in the latest CREP series has been released.
Likewise, vehicle and child restraint compatibility was included in both the original
and latest version of the program but methodology details have only been
published for the first series. Kelly and others (1996) described this procedure as
involving all child restraints being fitted into two positions in the rear of six
different vehicles. Each vehicle was one of the top four Australian selling models
in six different vehicle categories. The restraints were fitted into the left rear and
centre seating position. Observations and measurements were then made
regarding how well the restraint “fitted” each vehicle, or in other words, the
compatibility between each restraint and each vehicle.
Since a number of vehicles require forward front seat adjustment to allow enough
space in the rear compartment for installation of a child restraint, the CREP
compatibility assessment also includes an evaluation of front seat ‘comfort’ when
the child restraint is in place.
There is potential, however to make the ease of use assessment more objective.
A draft assessment protocol has been developed for Australian NCAP and is
being considered for both NCAP and CREP child restraint /vehicle assessments.
The draft protocol is included as an Appendix to this report. In brief, it sets out an
objective scoring system for assessing: installation instructions, use of adult seat
belt (belt paths and angles), location of top tether, ease of adjustment of top
tether tension, yaw rotation, adjustment of harness shoulder height, ease of
placing dummy in the CRS, ease of adjustment of harness, harness fit, clearance
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 24
to vehicle components, quick extrication of dummy (usually with CRS), ease of
maintenance (disassembly for cleaning).
Australian NCAP
In late 1999, the Australian New Car Assessment Program (NCAP) aligned its
test and assessment protocols with EuroNCAP.
NCAP assesses the crashworthiness of new vehicles and provides a star rating
for the protection provided to front seat occupants. The primary purpose of
providing consumers with useful information is to assist purchasing decisions.
From a road safety perspective this program is beneficial in that the purchasing
pressure applied by consumers on vehicle manufacturers for good safety
performance will drive vehicle designers to incorporate more and more safety
technology into their new vehicles.
Two types of crash test are used in the assessment - an offset frontal crash test
and a side impact crash test. The offset frontal crash is conducted at 64km/h. In
this test, the vehicle hits a crushable barrier and the crash forces are
concentrated on the driver’s half of the vehicle. The side impact test involves a
moving barrier, fitted with a crushable front, impacting the driver’s side of the car
at 50km/h. In both tests, anthropomorphic dummies with standard
instrumentation are used as surrogate occupants. The offset frontal test
occupants uses two adult Hybrid III dummies instrumented to record head, neck,
chest, upper and lower leg loads in the driver and front seat positions. In the side
impact test, a specially designed side impact dummy, the adult Euro-SID is
placed in the drivers position and injury measurements are recorded from the
head, ribs, lumbar spine, abdomen and pelvis of the dummy.
The EuroNCAP protocol also requires
two child restraints to be installed in the
rear seat of the vehicle being tested. The
child dummies used are the TNO P1.5
and P3, simulating 18 month and 3 year
old children respectively. In the offset
frontal crash the P3 sits behind the driver
and the P1.5 sits behind the front
passenger. The positions are swapped
for the side impact crash test. These child
dummies are instrumented with head and
chest accelerometers. Dummy movement
is recorded on high speed film and is
analysed to assess the movement of
each dummy.
Figure 7. ANCAP Offset Frontal Crash at 64km/h
Currently, under the EuroNCAP Assessment Protocol, child restraint
performance is primarily based on dummy injury measurements. EuroNCAP is
currently reviewing the assessment criteria, partly in response to concerns
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 25
expressed by Australian NCAP. These concerns are discussed in the next
section.
Since late 1999Australian NCAP has included child restraints and dummies (in
line with the EuroNCAP protocol) in vehicles being tested in both offset frontal
and side impacts. Due to the fundamentally different design of child restraints in
Australia, ANCAP does not currently apply the child restraint portions of this
protocol and hence does not report the results of child restraint performance.
Key Findings from Laboratory Research
The extent of laboratory, both sled and barrier, research conducted in Australia
has given Australian researchers an enormous amount of background
experience in the are of child restraint design and particularly child restraint
performance assessment.
Together with experienced gained from decade of real world investigations, this
experience means that Australian researchers have an informed grasp on the
qualities of child restraints that have particular significance on their ability to
protect children in the real world. The most important example would be a
restraint ability to limit head excursion and in turn to provide head protection. It is
for this reason, that most assessment programs and research programs
conducted in Australia to date have use head excursion (and in side impact, the
ability of a restraint to protect the head) as the primary assessment feature.
To some extent, this approach (and the experience underlying this approach) is
at odds with some developing assessment procedures elsewhere in the world, or
in the case of Euro-NCAP, assessment procedure currently in place.
Concerns about EuroNCAP Assessment Protocol
Based on a number of the key findings of Australian research to date, there are
two primary problems with the assessment protocol being used by EuroNCAP.
Firstly, the Euro-NCAP test method uses the TNO 'P series' dummies. Although
Australian Standards testing (and most regulatory most testing worldwide) uses
this type of dummy, the fact that the TNO P-series dummies are non-biofidelic
means that the use of such dummies in injury criteria based assessment is not
really acceptable. Trosseille and others (2001) sum up the problem with P-series
child dummies: "The current child dummies (P-dummies) were developed in the
late 1970’s and early 1980’s... To further improve child safety it seems necessary
to replace the P-dummies with child dummies that are not only more advanced,
but can also evaluate the protection offered to children in lateral impacts and the
interaction of children with deploying airbags. Indeed, P dummies are quite
rudimentary and are not able to evaluate the protection in detail"..."When the
CREST project started, only the conventional TNO P-series dummies were
available. It appeared very quickly to the experts that the behaviour of these
dummies was not biofidelic." (it is noted that co-author Schrooten is an employee
of TNO, the dummy manufacturer).
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 26
It is common in Australian child restraint tests with P-series dummies for the legs
to swing upwards and there is contact between the head and the legs. It seems
unlikely that humans will move in this way but, in any case, the head to leg
contact is far from being realistic since the properties of both the dummy head
and legs have no correlation with that of a human child.
Standards type testing does not include any biomechanical based performance
requirements. Instead, requirements mainly centre on ensuring that the child
restraints remains in tact and contains the test dummy in various impact
configurations. For forward facing child restraints, the European Standard and
the North American standard also includes a requirement related to a head
excursion limit. Although not a true biomechanical performance measure, as
discussed above, this is directly related to the restraints’ ability to prevent injury.
Euro-NCAP on the other hand primarily assesses child restraint performance
using injury criteria. An example of the criteria used for frontal impact is shown in
Table 1.
Table 1. EuroNCAP Frontal Impact Injury Criteria
P 1½ Child Dummy
P 3 Child Dummy
Parameter
1 point
scored up to
0 points
scored at and
beyond
1 point
scored up to
0 points
scored at and
beyond
Head
excursion *
450 mm *
550 mm*
450 mm*
550 mm*
Head Vertical
acceleration,
3 ms
exceedence
20 g
40 g
Not
measured
Not
measured
Chest
resultant
acceleration,
3 ms
exceedence
41 g
55 g
41 g
55 g
Chest vertical
acceleration,
3 ms
exceedence
23 g
30 g
23 g
30 g
Further, the protocol requires that “in the event of a hard contact occurring on a
structure other than the car interior, as indicated by either direct evidence of
contact or a peak resultant head acceleration in excess of 80g, the limits in” the
table 2 should be used.
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 27
Table 2: EuroNCAP Frontal Impact Head Contact Criteria
P 1½ Child Dummy
P 3 Child Dummy
Parameter
1 point
scored up to
0 points
scored at and
beyond
1 point
scored up to
0 points
scored at and
beyond
HIC 36
650
1000
650
1000
Head
Resultant
acceleration,
3 ms
exceedence
72 g
88 g
72 g
88 g
The overall score for each child restraint in frontal impact recorded for
assessment is the worst scoring parameter from the above tables.
Australian NCAP has included child dummies in its crash tests since late 1999.
All of the dummies were restrained in forward facing child seats with top tethers.
The results of these tests are shown in Figures 8 and 9. It can be seen that all
exceed the limit on vertical head acceleration (40g) and many exceed the limit on
vertical chest deceleration.
Figure 8. ANCAP CRS Measurements - head deceleratrions
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 28
Figure 9. ANCAP CRS measurements - chest deceleration
However, as stated above TNO P Series dummies are the prescribed dummies
in this protocol and these dummies are not, and have never had any claim to
biofidelity when used in forward facing CRS (Trosseille and others 2001). Most
significantly, there has never been any validated injury criteria set for use with the
TNO P series dummies. Given the excellent experience with CRS in Australia the
assessment criteria proposed by EuroNCAP are considered to be seriously
flawed.
There are, however, two different sets of proposed criteria available for use with
CRABI and child Hybrid III dummies. This data can not be extrapolated to the
TNO P- Series dummies because different dummies respond in different ways.
This has been clearly demonstrated both in Australian and overseas (Brown and
others 2001). Trosseille (2001) address the problem of assessing injury risk for
child in vehicle crashes: "The analysis of accidents involving children reveals that
child restraint systems (CRS) in compliance with European regulations give
highly contrasted levels of protection in real-world accidents. The main reasons
for this are on the one hand the lack of biofidelity of the dummies, and on the
other hand the insufficient biomechanical knowledge on injury mechanisms and
associated physical parameters. Unlike for the adult, child impact tolerance or
behaviour cannot be determined directly by experiments on human bodies...".
Melvin (1995) also points out the difficulty in obtaining injury tolerance for
children. For example, current neck tension tolerances are partly based on tests
of stillborn children conducted in the late 1800s (for use in obstetrics).
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 29
Australian work studying head acceleration results from sled testing using the
same child restraint subjected to same crash severity but using two different
dummies, illustrated significant differences in dummy response. The test involved
a frontal impact using the same impact conditions required by Standard Australia.
The head acceleration result obtained with the TNO dummy was about 200g,
while the result obtained with the CRABI six month dummy was in the vicinity of
60g.
Likewise the conditions under which the same dummy is tested can have some
influence. For example head accelerations obtained with the same dummy in an
impact of equal severity on a sled compared to in a full scale barrier test can
produce significantly different results. In one such comparison using the CRABI
six month dummy the peak head acceleration was 60g in the sled test, while in
the full scale barrier test the head acceleration was somewhat higher at 79g
(unpublished RTA Crashlab research).
Similar results were reported by Duma and others (1999) when they compared
the head and neck response of two different dummies,the Q3 dummy and the
Hybrid III three-year-old dummy. They found substantial kinematic and kinetic
differences between these dummies due to differences in head geometry and
mass, and neck stiffness. In addition significant difference were also noted in the
neck tension, flexion moment and lateral bending responses between the two
dummies.
The fact that different dummies responded differently to each other and the same
dummy will give different results depending on the test environment has two
important implications. Firstly, results obtained from similar test situations using
different test dummies cannot really be directly compared (in terms of
biomechanical performance). As a result, care needs to be taken when
comparing the responses obtained with the same dummy in different test
environments, even when testing occurs at similar severity. (In the sled v barrier
example here the main differences in test environment would be the crash pulse,
characteristics of the seat on which the child restraint was placed and the
geometry and properties of the seat belts used to anchor the child restraints.)
Secondly, injury assessment curves and values, however they are derived
cannot be transferred to dummies other than those for which they were
developed. This was also the conclusion of Duma and others (1999) following
their comparison of the Q3 and the Hybrid III three-year-old. They stated “these
tests suggest that separate injury criteria are needed for each dummy”.
The other major problem with the child restraint injury criteria used by
EuroNCAP is that there is no correlation between the performance limits set by
EuroNCAP and the risk of injury in the real world. In fact, currently there has
been no validation (in terms of real word injury potential) of any or the proposed
child injury criteria regardless of the dummy used (Brown and others, 2001).
All of these issues are extremely significant in discussing results, or
methodologies intended to evaluate child restraint effectiveness in the laboratory.
Basically the state of art of child dummies and child injury criteria means that
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 30
child restraint effectiveness cannot, with any scientific validity, be assessed in
terms of real world injury potential. Rather, as has been the case in Australian
research and assessment procedure to date, child restraint performance in the
laboratory can really only be evaluated
(i)
in terms of dummy movement
(ii)
in terms of relative protection
Therefore, at the current state of child dummy development, the only way to
realistically evaluate effectiveness is by studying how child restraints perform in
the real world.
STUDIES OF THE EFFECTIVENESS OF CRS
Most studies of child restraint effectiveness have used some form of real world
data. This data is usually gathered from one of two sources. These are; mass
crash databases or in-depth studies. Different types of data source provide
different levels of information. Sample numbers are much higher in mass crash
data investigations but the level of detail can be limited. On the other hand,
detailed information can easily be produced through vigorous investigation of real
world crashes, but the numbers involved are usually smaller and less
representative of any particular population.
Although estimates of child restraint effectiveness have been reported from a
number of different researchers around the world using data such as that
described, most estimates have been fairly general in their methodology. For
example, the effectiveness of child restraints, like any occupant protection
system, is going to depend on a number of variables that have the potential to
directly impact effectiveness. Most studies reported to date have not taken into
account variations introduced by different types of restraint systems, seating
position and crash severity and orientation. Incorrect use and/or inappropriate
use of different types of restraint by different age groups can also influence
effectiveness.
Subject to these limitations, overall estimates of effectiveness can be important
general indicators of potential injury reducing ability of restraint systems., as long
as the potential for other factors (such as crash type, seating position and correct
use) to influence the level of protection is kept in mind.
Overall estimates of effectiveness
Child restraints have been demonstrated in numerous studies, to significantly
reduce the risk of death and serious injury. In North America and Europe, studies
have estimated this reduction to be in the order of 70%. (Weber, 2000; Partyka
1990; Carlsson 1991; Tingvall 1987; Cuny 1997 and Isaksson –Hellman and
others 1997). Similar estimates of the effectiveness of adult belts in reducing the
likelihood of serious injury in the adult population have been in the order of 50%.
(Weber 2000; Huelke and others 1979; and Malliaris and others 1982). It
therefore appears that dedicated child restraints have the potential to reduce
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 31
injury risk by a greater extent than adult belts reduce the risk of injury in the adult
population.
There appears to have been little in the way of formal evaluation of child restraint
effectiveness conducted in Australia
In 1980, an estimation of the effect of NSW legislation requiring children under
eight years to be restrained found that this legislation reduced casualties by
about 30% (Herbert & Freedman 1980). However, this was not a true measure of
restraint effectiveness since this figure was based on reduction of all child
occupant casualties. That is casualty numbers included children restrained in
child restraints, seat belts and travelling unrestrained in the rear of the vehicle
and was not a direct before and after count for children of child restraint age.
A more recent Australian analysis was conducted in 1994. This study compared
injury in Western Australian child occupants two years and younger to that
reported for children of the dame age in NSW. The study found “children reported
to be wearing a restraint were 50% less likely to sustain an injury requiring
hospitalisation”. This figure refers to all levels of severity and is not confined to
the reduction in the more serious end of injuries (as was the case the North
American and European estimates cited above).
The most recent and most comprehensive Australian study of children and child
restraint performance in real world crashes was conducted in NSW throughout
the year 1993 (Henderson 1994; Henderson and others 1994). The primary
objectives of this study did not include the statistical investigation of the
effectiveness of child restraint systems but was designed to investigate the
general performance of the child restraint systems available at the time. The
ability of Australian child restraint systems to provide effective crash protection
was confirmed by this study. Of the 247 children aged 14 years or younger
included in this study, 228 were using some form of restraint and very few
sustained serious injury. This was the case even though the sampling methods
were such that data collection was skewed towards the serious end of crashes.
Figure 18 is reproduced from the Henderson (1994) report and illustrates the
restraint type by maximum AIS for all restrained children in the study. From these
figures it can be seen that 88% of the restrained children received injuries of a
severity MAIS 2 or less.
This study also provided valuable information regarding the types of injuries and
sources of injury observed in restrained children in Australia. Although not strictly
effectiveness studies, in-depth investigation of injury and injury mechanisms are
vital to ensuring optimum occupant protection (for both children and adults). This
type of study will be discussed in greater detail in the next section.
Problems with studies that simply attempt to report the overall effectiveness
without taking into account specific influential factors are particularly relevant to
the Australian situation. The effectiveness figures from Australian studies cited
above (50% - Herbert & Freedman, 1980; 30% Palamara & Stevenson, 1994)
are lower than those figures reported in North American and European studies,
but it is unlikely that this actually proves that Australian restraints are less
effective than their overseas counterparts.
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 32
In fact the performance of Australian child restraints in laboratory and in-depth
field studies suggests Australian restraints would have to be at least as effective,
if not more effective, than many of the restraints available in other countries. It
must therefore be remembered, that not all studies such as those cited above are
not designed to deliver true estimates of effectiveness.
At a recent Australian seminar regarding child restraint design, a claim was made
that Swedish restraints were much more effective that those in Australia. This
claim was based on the number of deaths due to road trauma for every 100,000
of population. This is a measure of the public health risk associated with road
trauma. Although these figures relate to all deaths including both adults and
children, it is useful to discuss them in terms of their appropriateness as a
measure of restraint effectiveness. This type of comparison does not take into
account the degree of motorization or the kilometres travelled. For child restraints
(and other restraint systems) there is also the complication that the total number
of fatalities does not separate
those who died while on the
road as vehicle occupants from
those who were killed riding
bicycles or as pedestrians. In
addition fatality rates presented
make no discrimination
between those unrestrained
and those using available
restraint systems. For these
reasons alone, it is
inappropriate to make
measures of effectiveness
based fatality rates.
One possible method of
accounting for exposure is to
compare fatality rates - that is
the ratio of persons killed to
persons injured. Figure 10
shows the results of a tentative
analysis of road accident
fatality rates for children (AIT
2001). This appears to indicate
remarkably low fatality rates in
the USA, Germany and UK
compared with Australia,
Sweden and France. However
there are numerous problems
with these data that make it
impossible to draw valid
conclusions:
Figure 10. Tentative Analysis of Fatality Rates. There are many
confounding factors that make this type of analysis invalid.
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 33
•
most rates are for all road accidents involving children, including pedestrians
and cyclists. New South Wales data are for car occupants only (RTA 2000).
•
The definition of "injury" is likely to vary considerable between countries.
•
For some countries samples sizes are small and resulting confidence
intervals are large (error bars on graph).
The main problem with this type of comparison, however, is that a system which
does well at preventing any injury, such as a well-designed CRS, is
disadvantaged because injuries only occur in the severest crashes.
Effectiveness of different types of child restraint
Unless otherwise stated, "effectiveness" compares outcomes with an
unrestrained occupant.
The differences in effectiveness, depending on the type of restraint (and the
inherent design of different types of restraint) can be seen from European and
Swedish studies. As Australian researchers would expect from experience
gained in the laboratory, it appears that rearward-facing restraints provide the
greatest level of protection. Most studies have estimated that rearward facing
restraints reduce the risk of serious injury by about 80-90% (Tingvall 1987,
Carlsson and others 1991; and Cuny and others, 1997). A recent analysis of the
Swedish Volvo crash database reported that the injury reducing effect of
rearward facing child restraints might be as high as 96% (Isaksson-Hellman and
others, 1997).
Estimates of the effectiveness of forward facing child restraints have been closer
to the 70% overall estimate of effectiveness (Weber, 2000; Cuny and others,
1997).
Also as Australian researchers would expect from laboratory experience, booster
seats (and belt positioning boosters) although providing improved protection
compared to an adult belt system, provide a lower level of protection than other
forms of dedicated child restraint. Carlsson and others (1991) reported that
forward facing booster type restraints in Sweden reduce the risk of injury by 3060%. Cuny and others (1997) in France estimated this type of restraint to reduce
injury by about 30%.
The highest level of injury reducing effect introduced by booster type restraints
was recently reported by Isaksson-Hellman and others (1997) from their analysis
of the Volvo crash database. These authors found the Swedish belt positioning
boosters reduce injury by about 77%. It is likely that these differences in booster
estimates indicate the potential influence of inherent design for any particular
‘type’ of restraint. Such differences design differences (and their likely influence
on effectiveness) are extremely relevant to the Australian situation where child
restraints of any particular ‘type’ can vary markedly from their European
counterparts. This provides another example of the difficulties encountered in
trying to compare the effectiveness of restraints between countries.
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 34
Estimates of the effectiveness of adult belts used by children have also been
made by a number of researchers. These estimates vary widely between 30%
and 60%. The effectiveness of the adult belts in protecting children appears to
depend on the age of the child (Partyka, 1988; Cuny and others 1997 and
Isaksson man and others, 1997).
The use of a lap belt compared to a lap/sash belt is generally estimated to
reduce the level of protection by about 20% (Mallieris & Digges, 1987; Lundell
and others, 1991).
Therefore in terms of the level of protection these studies have found that
rearward facing restraints provide the highest level of protection while adult belts
provide the lowest.
A final problem with comparing overseas mass crash data with Australian data is
the disparities in general occupant protection practices in Australia compared to
overseas. Most notable is the practice in some countries of carrying children in
the front passenger position, while in Australia, most dedicated restraints are
used only in the rear seats. As will be seen in later discussions, this difference in
practice suggests that Australian child restraint effectiveness estimate, if
conducted in a similar manner to those studies cited above would yield even
higher injury reducing rates.
Influence of seating position on CRS effectiveness
The rear seat (where children in Australia are most often positioned) has been
demonstrated to provide a greater level of protection for both adults and children
in an number of overseas studies (Kelleher-Walsh and others; Morris 1983;
Evans and others 1988; Partyka 1988 and Braver and others 1997). An analysis
of North American mass crash data found ‘rates of injury at any given severity
level are uniformly and monotonically declining in the following order:
unrestrained, front seated; unrestrained, rear seated; restrained, front seated and
restrained, rear seated.” (Morris, 1983)
However, somewhat surprisingly, some studies have failed to find any protective
benefits of the rear seat for restrained occupants (Kraft and others 1989). It is
possible that the absolute results of many of these studies, those that have found
positive effects for rear seating positions and those that have not, have been
confounded by the type of restraint being used (and possibly to some extent the
types of impacts). This issue is particularly significant if we note that most seating
position comparisons involve adult belt systems and there is a known difference
in the level of protection afforded by three point adult belts compared to two point
belts. Similarly the exposure of different age groups is likely to be different in
different seating positions. It is also likely that the usage rates of different seating
positions by different age groups will vary between different countries.
A very thorough recent study of risk of death among child occupants in front and
rear seating position was reported by Braver and others in 1997. This study
found an overwhelming increase in protection for rear seated occupants.
Variables such as restraint use, airbag status, restraint type, impact locations,
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 35
speed limit and vehicle type and their influence on the protection provided by the
rear seat compared to the front seat were studied. In summary Braver and
others found injury risk reductions for rear seat occupants in the following
circumstances:
•
An overall 36% reduction for children 12 years or younger.
•
An overall 32% reduction for occupants 13 years and over.
•
An overall 41% reduction for children aged 1-4 years.
•
An overall 30% reduction for children aged 5-12 years.
•
A 37% reduction in children not using restraints compared to non users of
restraints in the front seat.
•
A 38% reduction in restrained children compared to restrained front seat
occupants.
•
In vehicles without airbags in the front position, there was a 35% reduction for
children in the rear.
•
In vehicles without airbags the injury risk reduction in the rear ranged from
26% to 43% depending on the restraint status and type of restraint used by
the child in the rear (26% for unrestrained, 31% for those using adult belts
and 43% for those using child seats).
•
In vehicles with dual airbags there was an 80% reduction in injury risk for
children using dedicated restrains.
•
Benefits of rear seat positions were slightly lower in areas of high speed limits
compared to those of lower speed limits (33% in high speed areas, 48% in
low speed areas).
•
Type of vehicle had influence on the benefits of rear seat positions. Rear
seat benefits higher in midsize 2 door passenger cars (45%) than 4 door
passenger cars and midsize station wagons (28%).
•
Rear seat injury risk reductions depending on type of impact were
•
-
47% for frontal impacts
-
43% for rollovers
-
32% for side impacts
There was an increase in injury risk for children in the rear seat in rear
impacts. This was a significant increase (61%). But only 5% of fatal car
collisions involve rear impacts.
Crash characteristics and the effectiveness of CRS
As discussed above, different types of child restraint provide different levels of
protection, depending on crash conditions. Effectiveness of any restraint system
is therefore likely to be influenced by both the severity and type of impact.
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 36
Braver and others (1997) findings illustrate the type of influence crash severity (in
terms of impact speed) that crash conditions can have on restraint effectiveness.
Braver and others (1997) noted that the benefits of rear seat positions were
slightly lower in areas of high speed limits compared to those of lower speed
limits. Cuny and others (1997) also reported impact velocity to have a significant
influence on restraint effectiveness. In particular Cuny and others found that in
frontal impacts, both forward facing child seats and booster seats provided lower
levels of protection in impacts of higher velocity. For booster seats they reported
an 80% reduction of MAIS 2 and greater injuries in impacts occurring at less than
40km/h and a 23% reduction in impacts of 40km/h and greater. In addition, the
reductions in higher impact velocities found in forward facing child seats were not
as large as those observed in the case of boosters. In frontal impacts, with
impact velocities of less than 40km/h Cuny and others (1997) found forward
facing child seats to provide an injury reduction of MAIS 2 and greater injuries of
78% while in impact velocities of 40km/h and greater, the injury reducing effect
was 65%.
Braver and others (1997) also noted differences in the level of protection
depending on impact orientation. They found rear seat injury reductions were
47% for frontal impacts; 43% for rollovers; 32% for side impacts and an increase
in risk of 61% in rear impacts.
For child restraint systems the greatest difference in effectiveness has been
noted in injury and survival rates that occur in frontal and side impacts. Side
impacts are much more likely to result in serious and fatal injuries to children
than frontal impacts (Braver and others, 1998; Rattenbury and others 1993,
Langweider and others 1996). Weber (2000) sums up these type of findings by
stating that “approximately twice as many crashes with a child fatality are frontal
compared to lateral, but side impacts are nearly twice as likely to result in a child
fatality regardless of restraint status and seating position”. French and German
studies have confirmed these findings and gone further to demonstrate that the
fatality rate of children involved in frontal impact is the lowest of all crash
configurations while in side impacts the fatality rate is the highest (Langweider
and others 1996, Vallee and others 1993). Henderson (1994) noted in the
Australian study of real world crashes involving children that “ side impacts were
the crash configuration most likely to result in significant injury’. Hummel and
others (1997) note that the risk to children on the struck side in side impacts is
particularly high.
Rear impacts have also been observed to pose a significant risk for children
restrained in rear seats. However, the overall frequency of severe rear impacts is
generally low (Braver and others 1997; Vallee and others 1993).
STUDIES OF REAL WORLD CRASHES
Most of the effectiveness studies discussed above involve the analysis of mass
crash data. Effectiveness can also be studied by in-depth investigation of real
world crashes but such investigations do not usually involve enough cases to
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 37
yield statistically significant estimates. In-depth studies can, however provide
essential information regarding the good and bad performance characteristics of
child restraint design. Design characteristics and their influence on protection is
probably best studied through investigations aimed at identifying the type and
pattern of injuries sustained by both restrained and unrestrained children.
In-depth real world impacts involving child occupants have been studied by
numerous teams of both Australian and overseas researchers. These studies
have included all levels of investigation.
Investigation of injury type and pattern can also be studied using mass crash
data, however in such studies identification of injury patterns is usually the
primary aim and hence overall effectiveness estimates have not been attempted.
Injuries to restrained children
One of the most interesting thing from review of Australian and international indepth child occupant/injury pattern studies, is that a number of very similar
findings regarding the overall injury pattern has been reported by a number of
researchers. The most important of these are that most injuries suffered by
restrained children are minor, the head (and face) is the most commonly injured
region, and the head is the most seriously injured region. The type of study or
where in the world the study is conducted appears to have no bearing on this
overall pattern of injury to restrained children.
It should be noted that the head is also the most frequently injured and frequently
seriously injured region of unrestrained children in the real world impacts. But
according to Upledger et at(1997) the incidence, and severity of head injury
among unrestrained children is much higher than seen in restrained children).
(Henderson, 1994; Rattenbury & Gloyns ,1993; Tingvall, 1987; Agran and others,
1988; Upledger and others, 1997; Newgard and Jolly in 1998; Isaksson-Hellman,
1997; Khaewpong and others 1995).
In the real world, the type of injury sustained by any restrained child, like the
effectiveness of any particular restraint is complicated by many different
variables. In terms of injury the most influential variables are: age range, type of
restraint, seating position, crash type and crash severity. The influence of these
factors is discussed in detail below.
The influence of restraint type, seating position and crash characteristics
on injury pattern
Although the head remains commonly injured region in all children involved in car
accidents, studies have shown that factors such as those listed above all
influence the severity of injuries and the pattern of injuries over the rest of the
body.
Age range influences are intimately related to those of restraint type, since
restraint design vary (sometimes slightly, and sometimes significantly) for
different age ranges of children. This means that although some researches have
reported age related differences, in most cases these differences can generally
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 38
be explained by differences in restraint system (and their appropriateness for the
specific grouping of ages in any particular study).
For example Agran and others (1997) looked at the injuries suffered by three
groups; 0- 3 years, 4- 9 years and 10 –14 years. They found that in the injuries,
in the 0-3 age group no other region besides the head appeared to suffer injury
with any significant frequency. They noted that in this age group the most
infrequently injured regions were the chest, abdomen and spine. However in the
4- 9 age group the author’s found a significant rise in the number of injuries to the
abdomen and the extremities. And spinal strains began to be prominent in the 10
– 14 year age groups. The author’s also noted that there was a relative decrease
in the number of head injuries suffered by this older age group. Newgard and
Jolly (1998) reported similar findings. They analysed a database consisting of
2141 child passengers and grouped the children into those aged 1 year, 1-4
years, 5-10 years and 11-16 years. Like the Agran and others (1997) study,
these authors found that for children under 4 years, the head region was the only
body region that was injured with any significant frequency. In terms of head
injury in this age group the findings reported were more specific than the Agram
and others (1997) study. For instance Newgard and Jolly (1998) reported that for
children aged less than one, minor facial injuries were the predominant type of
head injury (60% of the sample). And only 1 in 10 of the total sample (of children
under 1) actually had a “head” injury, but 40% of these head injuries were
serious. A similar pattern of facial and head injuries were observed by Newgard
and Jolly in their 1-4 year group. But here (unlike Agran and others) they also
noted an increase in frequency of abdominal injuries and injuries to the
extremities.
Newgard and Jollys (1998) findings for their older age ranges were also similar to
that reported by Agran and others (1997). In the 5 – 10 years age group the
extremities and the abdomen were also injured with significant frequency,
however of interest is the appearance of significant numbers of injuries to the
chest and spine. In the oldest age group, 11-16, injury to the extremities and the
spine occurred in even greater numbers than injuries to the head and face. The
children on this study less than 1 years old were almost all using a child restraint
(50%) or were unrestrained (43%). Most of the children 1 – 4 years were using
an adult belt (42%) or a child restraint (34%), but a significant number were
unrestrained (24%). Most of the 5-10 years children were also using adult belts
(63%) but again a significant number were also unrestrained (37%). Similar
proportions of restraint use were observed in the oldest group (11-16) with 55%
using adult belts and 45% unrestrained. Newgard and Jolly (1998) did not
discriminate between children restrained and unrestrained in describing the
frequency of injury to different body regions.
The findings of both these studies, demonstrate how similarities and differences
can be largely be explained by the type of restraint being used by the majority of
the children in each age range.
A number of more in depth studies of children in car crashes have studies the
importance of type of restraint on injury patterns in detail. Because of the nature
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 39
of these type of investigations, these studies have involved much smaller sample
numbers. Khaewpong and others (1995) using a sample of 103 children reported
that. that for children in infant seats (birth to 9kg) the only body region injured
with any significant frequency was the head. For children in convertible child
restraints (birth to 18kg), the head and the face were the most frequently injured
regions with 79% of the children receiving head injuries and 71% receiving facial
injuries. The upper extremities were also injured with some degree of frequency
in this age group (29% of children receiving injuries). In booster seats the head
and face was also the most injured, however injury to the abdomen was also
observed in 42% of the children. In children using lap belts, the abdomen was the
most frequently injured region (78% of the children), followed by the face (59%),
head (44%) and chest (26%). In lap/sash belts Injury appeared to be generally
more widespread with the following frequencies; face 67%; head 60%; abdomen
60%; upper extremities 40%; neck 33%; chest 30%; and lower extremity 23%.
By superimposing age ranges on to these restraint types the similarity between
this study and those of Agran and others and Newgard and Jolly becomes
evident.
The significance of abdominal injury in children using belt-positioning boosters
was also highlighted by Troisseile and others (1997). The authors noted that in
an analysis of French crash databases, abdominal injuries occurred in similar
frequencies for children using booster seats as they did for children using adult
belt systems alone.
Henderson (1994) also described the types of injuries sustained by children
using different types of restraints in Australia. This study consisted of a sample of
247 restrained children aged 0 to 16 who were using infant restraints, child seats,
belt-positioning boosters and adult belts. Most of the children in this study
received only minor injuries (AIS 1) or moderate (AIS 2) injuries (80% of sample).
Specific information related to the body regions injured in each type of restraint
was only provided for the more serious injuries. Head injuries were the
predominant serious injury observed in both children restrained in infant seats
and forward facing restraints. Head injuries were also the most often observed
serious injury in children using booster seats, although injury (fractures) to the
extremities were also observed in a number of these children.
A large number of the children in the Henderson (1994) study were using
lap/sash belts (almost 50%). The pattern of injuries suffered by these children
was similar to that described by Khaewpong and others (1995). That is, in
general the injury was more widespread and the head/face and extremities were
the regions most often injured in the children using adult seta belts. However in
the Henderson (1994) study, the neck, chest and abdomen of children using
lap/sash belts were injured with almost the same frequency as the head. Also
similar to the Khaewpong and others (1995) study, Henderson (1994) reported
the head and the abdomen to be the most frequently injured regions in children
using lap only belts.
Isaksson-Hellman (1997) also described the pattern of injury sustained by
children using different restraint systems. This study, using a Swedish crash data
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 40
base included only rearward facing child restraints (used by children 0-3), belt
positioning boosters and adult belts (used by children over 3years). The authors
found almost no injury at all in their sample of rearward facing restraints. Only 3
injuries were reported from a total of 421 children and these were all relatively
minor. They involved two instances of leg fracture and one minor brain
concussion. For belt positioning boosters their observations agreed somewhat
with that reported by others ie: the most frequent body region injured was the
head. However they also reported a relatively high frequency of serious spinal
injury and some chest injuries using this restraint system. The same widespread
pattern of injury in children using adult belts was observed. The authors also
noted that spinal injuries in older children were typically positioned in the thoracic
regions while spinal injuries to small children were mainly found in the cervical
region.
One or two studies have also attempted to study differences in injury patterns
depending on the type of impacts and where in the vehicle the child was seated.
Agran and others (1989) reported an increase in spinal injuries in children
restrained in the front seat of vehicles involved in rear impacts. These author’s
also noted more severe head and facial injuries occurred in same side child
passengers involved in side impacts compared to children in other seating
positions and in other types of impact. Interestingly Khaewpong and others
(1995) found the opposite, i.e. more severe head injuries in the far side seating
position in side impact. A possible explanation for this is non struck side child
restraints without top tethers will pivot and point towards the area of
impact/intrusion, while struck side child restraints are engages directly at a lower
level by the side of the car
Isaksson-Hellman and others looked in detail at the frequency of injury to specific
regions (head, spine and abdomen) in frontal impacts and side impacts. They
found that for children restrained in belt-positioning boosters, serious head injury
occurs at about the same rate for both frontal and side impacts. However for
children restrained by adult belts serious head injury appears to occur much
more frequently in side impact. Spinal injury was found to be more common in
frontal impacts for both types of restraint system. Abdominal injury in children
using belt –positioning boosters was found only in frontal impacts while for
children in adult belts in occurred in both frontal and side impacts (albeit much
more frequently in frontal impacts.)
Injury sources for restrained children
Studies that describe injury sources for restrained children are also important to
understanding the good and bad characteristics of child restraint practices.
An example of such a study where sources of injury, by injured body region, were
described in some detail is the study by Khaewpong and others (1995). For
head injuries, these authors found that most serious injury occurs following a
head strike with an interior hard surface. The surface struck depends on the
seating position and the type of restraint used. The types of surfaces involved
include the instrument panel, dashboard, A and B pillar, interior door panel and
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 41
doorframe. Minor head injuries, in most cases, were attributed to contact with the
restraint system itself. For facial injuries the authors noted that most injury to this
region was minor involving cuts and bruises but no injury source was described
for these injuries.
The overwhelming source of neck injuries in the Khaewpong and others (1995)
study were due to contact with seat belt webbing. Inappropriate use of adult belts
was also observed to be a causal factor of injury to this region in a significant
number of cases. No specific contact/causal factor for upper extremity injury was
observed. For chest injuries, the authors noted that this was primarily a problem
for children using adult belts. Serious injury was most often caused by contact
with hard interior surfaces while minor injury could be attributed to contact with
softer surfaces and the restraint system itself. Pelvic and abdominal injury was
also really only a problem for children using adult belts, particularly lap only belts.
And 90% of these injuries arose from contact with the restraint system. Lower
extremity injuries were reported to have occurred most frequently when the
restraint system was correctly used and the occupant was seated in the rear, no
specific injury source was identified.
Contact with the hard interior was also described as the major source of head
injury in restrained children in Sweden (Isaksson – Hellman and others 1997).
Fatal spinal injuries were also reported to have occurred in conjunction with head
contact with interior surfaces. The authors noted that spinal injury mainly
occurred in frontal impact and was associated with belt use. Abdominal injuries
were mostly attributed to inappropriate belt geometry for children using adult
belts systems.
Troiselle and others (1997) believe the majority of abdominal injuries observed in
children using belt positioning boosters is caused by the design of many boosters
which allow children to submarine the lap belt.
The Australian study conducted by (Henderson, 1994) reported the types of
injury source for different types of restraint system in great detail. For rearward
facing restraints, Henderson (1994) reported serious injury to mainly occur
following contact with the vehicle interior. In most cases this involved intrusion of
the vehicle. In forward facing child restraints, Henderson (1994) also noted that
most head injury occurred following contact with a surface of the vehicle interior.
Injuries to the neck, chest and abdomen (all mainly minor) were attributed to
contact with the restraint system. Injuries to the extremities were found to have
occurred following contact with vehicle door, other seats in the vehicle and other
child restraints in the vehicle. Minor injuries involving bruises and abrasions were
found to have occurred predominantly by contact with restraint webbing.
Lacerations were mainly due to flying glass.
With respect to forward facing child restraints Henderson (1994) concluded
“injury is most likely to be a result of intrusion, contact with nearby parts of the
vehicle interior and other occupants, invasion of the child’s space by collapsing
seta backs, flying glass and other such mechanisms. Injury is unlikely to occur
from the forces of deceleration alone.”
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 42
Serious head and neck injury observed in children using boosters by Henderson
(1994) was found to occur in conjunction with misuse and was mainly related to
head contact with the vehicle interior. Extremity fractures observed in children
using this type of restraint were found to occur following contact of the extremity
with other seats in the vehicle, other child restraints in the vehicle and the
dashboard. Minor injuries sustained by children using booster seat predominantly
involved bruising from contact with seat belt webbing.
Head and facial injury sustained by children using adult belts was also mainly
found to be caused by contact with the vehicle interior. Contact sources included
the console, the door or window, other car seats, the roof, the windshield, and
dashboard. Flying glass was also a common source of injury for these regions.
Injuries to the neck, thorax, spine and abdomen were almost all attributed to the
seat belt. Injuries to the extremities occurred mainly as a result of contact with
parts of the vehicle interior. There was also a number of minor neck injuries
reported in children using adult belts in which there was no contact.
A major study of children injured in car crashes is being conducted by The
Children's Hospital of Philadelphia. The study has collected data for over 150,000
car crashes. From these important cases are selected for more in-depth studies.
To date, published research findings have covered low usage of booster seats by
children around 4 years of age, injury patterns in side impact crashes, facial
injuries, extra risk of side facing seats in pick-up trucks and injuries from seat
belts (CHOP 2002). One of us (Griffiths) is on the Advisory Board for this study.
Survival of children in severe crashes
Some in-depth studies have looked at severe crashes where children were not
seriously injured, primarily understand why the restraint system worked so well.
Many of these crashes come to attention due to adult fatalities.
Henderson and others (1994) describes several cases from the CAPFA study
where children survived severe crashes. Figures 11a to 11b illustrate some of
these cases. Henderson concludes:
"There are few safety devices that are as effective as child restraints. We found in
our study that the only injuries caused by deceleration alone were bruising and
abrasion from loads imparted from harness and seat-belt webbing, and there were
no cases of cervical spine injury in high-speed frontal impacts when restraints were
correctly used. The head remains the most important part of the body to be
protected. The principal threat to the restrained child is from invasion of the child's
space through impact intrusion, collapsing seat backs, and flying glass and loose
objects. The child is also at risk if allowed to move out of its space, and restraint
design should place a high priority on the minimisation of excursion of the upper
body in order to prevent head contact."
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 43
SOME CASES FROM THE CAPFA STUDY
Herbert and others (1974) report on
similar remarkable cases during the
early years of experience with top
tethers.
For more than two decades the NSW
RTA has informally monitored reports of
fatal road crashes and, where possible,
has investigated cases involving serious
injuries to children. During that time no
cases of severe injuries caused by
deceleration forces alone have come to
attention, where the children were
correctly restrained in a properly
installed child seat. Serious misuse or
gross intrusion have been the main
factors in the few cases of severe injury
or fatality.
Misuse of CRS
Restraint systems designed for use by
children have been shown to be
extremely effective in preventing injury.
However to provide optimum benefit
they must be used by appropriately
aged children and be used correctly. In
some cases, incorrect use of a child
restraint can actually increase the risk of
injury or the severity of injuries
sustained by children in crashes.
Misuse is a common problem. In North
America, recent observational surveys
have shown that about 80% of child
restraints were not being used as
intended (Weber, 2000) Misuse rates
are lower in Australia but are still a
concern.
Figure 11a. Two year old child in FFCR in centre rear
position uninjured.
Figure 11b. 18 month old child in FFCR in left rear seat
uninjured
Figure 11c. Nine month old child in FFCR sustained only
bruising.
Misuse of CRS in Australia
CRS misuse has been regularly
monitored in Australia and this has led
to improvements to the Australian
Standard.
Figure 11d. Three year old in FFCR in centre rear seat
broke arm from adjacent occupant. Three adults killed.
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 44
Top tethers
An early concern with top tethers was that they might not be used. This concern
may have been a factor in the reluctance, in the 1970s and 1980s, of USA and
Europe to use top tethers. Australian experience showed that these concerns
were unfounded after the initial implementation period. The latest usage survey
revealed less than 5% of child seats in New South Wales were being used
without a top tether (Paine and Vertsonis 1998). In any case, early crash studies
revealed that the CRS still performed reasonably well when restrained solely by
the adult seat belt - an undesirable situation, but not necessarily dangerous.
Use of adult seat belt for attaching CRS
Amongst the range of CRS available in Australia there are a variety of methods
by which the adult seat belt is intended to be threaded through the CRS. Adding
to the complication faced by carers is that "convertible" style CRS, that can be
used facing rearwards or forwards, have separate belt paths and adjustment
mechanisms. Partly as a result of this complication, about 12% of forward facing
child seats in New South Wales had the seat belt threaded incorrectly (Paine and
Vertsonis 1998). This was the dominant form of misuse of forward facing child
seats. Many of these cases were confined to a few older designs of CRS where
the belt could be threaded two ways and looked correct. In these cases the
"incorrect" belt path still provided adequate restraint and, by itself, was generally
not a serious safety hazard.
Harness adjustment
A loose harness increases the loads applied to the child, increases the forward
excursion of the child and increases the likelihood of a child wriggling partially out
of the harness.
The quality of harness adjustment can only be reliably assessed with a child in
the CRS. This is difficult to achieve in the field and the assessment is likely to be
subjective. Subject to this uncertainty, the proportion of loose harnesses in
Australia is likely to have decreased as CRS designs have improved. The
provision of a single point of adjustment of the harness has contributed to this
improvement.
Consequences of misuse
Different types of misuse can have different effects on child restraint
performance. The most common forms of misuse are relatively minor, resulting in
sub-optimal levels of protection. While some extreme forms of misuse can in
themselves lead to injury in a crash where otherwise no injury would have
occurred (Weber, 2000). Misuse problems observed in the North American study
cited above were mostly of the minor type. Likewise installation problems
observed in the recent Australian study were found to be minor in nature,
primarily related to the “tightness’ of both forms of anchorage. (i.e. the adult belts
and top tether) and the child restraint harness (Paine, 1998).
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 45
Field studies investigating injury in restrained children have found that some form
of misuse is commonly involved in cases where restrained children are injured.
(Henderson, 1994; Gotschall C and others, 1997, Rattenbury & Gloyns, 1993
and Weinstein and others 1997).
Henderson (1994) highlighted the role of misuse in crashes included in his
sample of children using forward facing child restraints in Australia. He reported
that of the 38 children using forward-facing restraints, 5 were using their
restraints incorrectly at the time of the crash. Four of this five were associated
with injury or death. Even more important is the observation that in the children
using rearward facing and forward facing restraints, only five received injuries
with a MAIS greater than 2. Almost all of this serious injury was associated with
some form of misuse.
The most comprehensive study to date of the role restraint misuse plays in injury
to restrained children was presented by Gotschall and others in 1997. These
authors studied the circumstances surrounding injury to all children 0 -12 years
admitted to a major North American trauma centre following a motor vehicle
crash. They found that 36% of the children admitted to the centre has been using
their restraint incorrectly. And this incorrect use was associated with greater
injury severity. Of particular interest was their observation that all fatal cases in
their study involved incorrect use. Weinstein and others (1997) also reported
similar findings. They found all but 1 of the 10 children fatally injured in their
sample of 207 children, was using their restraint system incorrectly or
inappropriately.
Inappropriate use is a subtle but widespread form of misuse. It involves the use
of a restraint by children outside the age (or height and weight) range for which
that type of restraint is designed. Gotschall and others (1997) found that more
than 76% of their sample were ‘inappropriately’ restrained. (Although it should be
noted that the definition of inappropriate use employed in this study included
children using adult belts when they were still within the height/weight range for
booster seats.) The effect of this form of misuse on injury severity was studied in
detail by Weinstein and others (1997). They found a large number of children
tended to move into the next stage of restraint before they had reached the
appropriate size for that restraint system. A similar tendency was observed by
Isaksson-Hellman and others (1997) in their Swedish sample. These authors
noted that their sample included a significant number of children who would not
have sustained injury if the most optimal child restraint system had been used. Of
interest is their related finding that restrained children were more likely to be
injured when they were at the youngest age for which the system they were
using was recommended.
Reducing the incidence of misuse is one of the primary objectives driving the
development of the universal or rigid CRS anchorage systems. Such a system
has the potential to alleviate problems with installing restraints into vehicles. For
installation problems with the current methods of anchorage, and problems with
securing the child in a restraint, the International Standards organisations and a
couple of other bodies have developed standardised methods of assessing an
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 46
individual restraints potential for and consequences of misuse. To ensure
dangerous misuse practices are minimised, Weber (2000) suggests such
manufacturers should use such methods in the process of developing new
restraints.
VEHICLES FACTORS AFFECTING CRS PERFORMANCE
In discussing the effectiveness of child restraint systems, it is clear that restraint
type, seating position and crash characteristics all have some influence. However
one particular factor has been poorly studied - the characteristics of the vehicle in
which the restraint is fitted. Vehicle factors and their influence on restraint
effectiveness are beginning to emerge as an area worthy of more detailed
studies. This is particularly true in respect to the European move to include the
performance of child restraints in individual vehicles as part as an overall rating
of the safety of that vehicle. Vehicle factors influencing child restraint
performance are discussed below.
Anchorage systems
As discussed in respect to laboratory child restraint work, the level of protection
provided by child restraints depends greatly on how well the restraint is tied to
the vehicle. Optimum performance therefore depends to some extent on the
characteristics of the combination of restraint design and anchorage system
design.
The fit of a restraint system in any vehicle will also be influenced by both the
anchorage design and the characteristics of the vehicle seat.
Australian child restraints designed for use by children from birth to
approximately 4 years must be anchored to a vehicle using the existing adult belt
system and a mandatory top tether. The use of top tethers requires an
appropriate anchorage location on the vehicle. In conjunction with the
introduction of the mandatory top tether requirements in Australia (as discussed
at the beginning of this paper), an amendment to the relevant Australian Design
Rules was also introduced in the mid 1990s.
This required the inclusion of at least one
anchorage fitting (bolt and lug) in every car sold
in Australia. Extra top tether anchorages, and all
anchorage fittings, in vehicle manufactured prior
to this time had to be installed either by the
parent or some other appropriate party. This
was one of the primary factors influencing the
set up of a Restraint Fitting Station network in
Australia.
Figure 12. Top tether components:
The mandatory requirement of a top tether
straps, clip, lug and bolt
anchorage with fittings made Australian child
restraint practices relatively unique compared to elsewhere in the world.
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 47
This difference in anchorage system between Australia and most of the rest of
the world also adds complexity to attempts at comparing effectiveness estimates
from overseas with the Australian situation. Laboratory (and to some extent
Australian field studies) have demonstrated that the greatest scope exists for
improving the overall performance of restraints is in side impacts. In the
laboratory one of the proven methods for achieving such an improvement is by
modifying the current anchorage system. Since the geometry and rigidity of the
two lower anchorages have been shown to have the most influence on the lateral
stability of the child restraints in side impacts, side impact protection could be
greatly enhance by the ISOFIX concept.
In terms of restraint effectiveness, laboratory testing of rigid (and semi rigid)
ISOFIX type anchorage systems has been conducted both in Australia and
elsewhere in the world. The main benefit of these systems is their ability to
reduce sideways movement of child restrains in side impacts (Kelly and others
1995, Brown and others 1997). In frontal impacts it is expected that such
systems will provide little additional protection to that already being provided by
Australian child restraints and current anchorage systems (unlike overseas
designs that rely solely on the adult seat belt). However where there are currently
incompatibilities between CRS, seats and seat belts, the ISOFIX system has the
potential to improve performance in frontal crashes.
Method of attachment to ISOFIX anchorages
The original ISOFIX concept was to require rigid attachment to lower
anchorages. As indicated earlier, the USA has decided to allow flexible
attachments to these lower anchorages. With respect to the rigid versus semi
rigid attachment systems, an Australian study reported in 1997 (Brown and
others) compared the performance of two point rigid lower anchorages with and
without top tether with semi-rigid or webbing based lower anchorages with and
without top tether. This work confirmed the ability of the rigid system to
significantly improve the performance of Australian child restraints in side impact.
Contact between the child restraints tested and a simulated side door structure
was completely prevented by the rigid system in both 45º and 90º side impacts.
The semi-rigid or webbing based system was found to provide some
improvement over the current Australian system. In particular there was a slight
reduction in the sideways movement of the child restraint system and contact
with the door was prevented in 45º impact. The authors believed that for these
reasons, such a system "may be useful as an interim measure in the move to
introduce improved universal methods of anchorage". They did note however that
the webbing based system allowed more sideways movement than the rigid
system and to ensure optimum performance of webbing based systems careful
consideration should be given to the characteristics of the flexible coupling. For
example they suggest the flexible couplings should be kept as short as possible
and be attached to the child restraint as low down and as far back as possible.
They also believe the addition of self-adjusting retractors could assist the overall
performance of such a system (Brown and others, 1997).
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 48
Currently there are a small number of vehicles available on the Australian market
that have ISOFIX anchorages. However there are no child restraints available in
Australia for use with such systems. In addition there is no Australian Design
Rule or Standards Australia document available regarding these universal or rigid
anchorage systems. This situation is currently under review. It is likely that any
CRS that is designed to use ISOFIX lower anchorages will also need to have
provision for attachment using the adult seat belt (plus top tether) to ensure the
CRS can be used in any vehicle. This situation may change when ISOFIX
anchorages become common or CRS are developed for specific vehicles (under
the current Australian Standard they are required to be suitable for universal
use).
Anchorage geometry
With respect to the current Australian anchorage system, the most important
vehicle features influencing child restraint performance are the geometry of the
tether anchorage points; the characteristics of the seat belt and the design of the
vehicle seat itself. Performance issues related to the location (and length of the
top tether strap) have been covered earlier in this paper. Potential problems in
achieving tight coupling between the vehicle and child restraint exist when the
location of the anchorage point is too close to the seat back. The influence of
seat belts and seat back characteristics are discussed below.
Seat belt characteristics
Since the current method of anchorage relies on the existing seat belt systems,
the geometry of seat belt anchorages has the potential to affect child restraint
performance. In the mid 1990's it was noted by Australian researchers that in
many cases seat belt geometry (presumably optimised for adults) was not
amenable to good child restraint installation. Often the top anchorage (or
shoulder strap anchorage) was forward of the front surface of the vehicle seat.
Such geometry would allow unwanted additional forward motion of the child
restraint. Lap belt geometry has also been found to be incompatible with good
child restraint installation. This has recently been demonstrated in unpublished
mathematical modelling work described in detail in earlier in this paper.
According to Griffiths and others (1994), lap belt geometry problems principally
exists because child restraint manufacturers do not make sufficient allowance for
the variability of lap belt geometry and buckle strap length in their design. Buckle
size can also produce incompatibility issues (Griffith 1994, Weber 2000). A
recommended practice related to these issues has been published by the Society
of Automotive Engineers - J1819; Securing Child Restraint Systems in Motor
Vehicles.
Insufficient seat belt length has also been found to be a problem in a number of
vehicles in the past. The main problem being that belts were not always long
enough to be routed around the restraint as directed by the child restraint
manufacturer's instructions (Kelly and others, 1996).
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 49
Retractable seat belts can exacerbate seat belt geometry problems. One of the
general problems with some retractable seat belt systems is that they sometimes
allow slack or reel out to occur prior to loading. To overcome this problem a
number of seat belt enhancements have become available. These include
webbing clamps and pre-tensioners. While the advantages of these seat belt
enhancement technologies for adult occupants has been well documented, little
investigation of their influence on child restraint performance has been reported.
One study reported by Czernakowski and Bell (1997) investigated the effect of
seat belt pre-tensioners on child restraint performance. They found that on the
whole pre-tensioners did improve the frontal impact performance of the child
restraint systems tested. Belt pre-tensioners reduced head excursion and
acceleration. The effect on neck loads was not monitored. The authors did note
however that the effect of the pre-tensioners was different for different restraint
systems with some showing little benefit. They believe that the influence the belt
pre-tensioner depends on the design of the child restraint system with respect to
the adult belt routing.
Although no studies regarding the influence of webbing grabbers or clamps have
on child restraints have been reported, it is likely the overall influence would be
similar. For these reasons it is probably important for child restraint
manufacturers (and vehicle designers) to consider the potential for improving
performance by designing seats compatible with such seat belt systems
(Czernakowski & Bell, 1997).
So far seat belt pre-tensioners and webbing clamps are rare in the rear seats of
Australian vehicles.
Vehicle seat characteristics
In addition to the properties of the anchorage system, how well a restraint fits into
a vehicle will also depend on how snugly the contours of the child restraint match
the contours of the vehicle seat. Both the vehicle seat cushion and vehicle seat
back is important. The compatibility between any individual restraint system and
the shape of the seat has its main influence in terms of stability. A poor match
between child restraint and seat shape can also magnify any belt geometry
inadequacies leading to poor performance in a crash. The major problem in
trying to address this issue is that the compatibility will depend on the specific
design of any child restraint and specific design of vehicle seat. A restraint that
has been designed to match one vehicle seat well may not necessarily match as
well with other seats. The move to include child restraint assessment in NCAP
programs vehicle may work to overcome this problem to some extent. Since
vehicle manufacturers will begin to look for those restraints most suited to their
vehicles. Likewise rigid anchorage systems remove a lot of the interaction
between the vehicle seat and the base of the child restraint and will therefore
assist in overcoming this sort of problem.
Possibly more significant is the influence between the properties of the vehicle
seat could have on the child restraint during an impact. Even in restraint
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 50
system/vehicle seats with good compatibility, seat properties such as cushion
stiffness can influence the overall performance of the restraint system. For this
reason, the performance of restraint systems in standardised tests, which use a
standardised test seat, should not be taken to be representative of how restraints
will perform in all real vehicles. In particular it would be expected that child
restraints in vehicles with seat properties on the extreme ranges of the ‘average’
seat used in standards tests would produce noticeably different results than that
observed in the Standard test.
Fortunately the use of a top tether in Australia reduces the adverse influence of
seat characteristics, compared with CRS with no top tether.
Child restraint interaction with airbags
In the USA serious problems have been reported in the interaction between
rearward facing restraints and front passenger seat air bags. The problem arises
due to airbag striking theses restraints during the airbag inflation process. The
force involved in the inflation of the airbag is extremely large and accelerations
have been measured in child dummy heads in these situations within the range
of 100 to 200g. To date there have been 18 infants killed in the US in this
manner, more than half were correctly restrained and the crashes have all be
otherwise survivable. (Weber, 2000). This has not been a problem in Australia,
mainly because child restraints are predominately used in the rear seat.
Weber (2000) reports that airbags in the front passenger position have the
potential to cause serious and even fatal injuries to all children using this seating
position regardless of type of restraint. She cites studies that have shown that the
presence of an airbag in this position can increase the risk of fatal injury to a child
using this position by about 34% -70%. The exact estimate depending on the
type of analysis. Note, however, that there is no information about the type of
restraints involved or the level of misuse. It could be expected that a CRS without
a top tether or a misused CRS that allowed greater occupant excursion would
expose that occupant to a much greater risk of injury.
There have been no reports of similar injuries and fatalities to children occupying
the front passenger position of vehicles equipped with dual airbags in Australia.
In a review of this problem presented by Griffiths (1997), he suggests that the
Australian practice of not carrying children in child restraints in the front seats
coupled with high restraint usage rates means that it is unlikely that this will
become a problem in Australia.
Both Griffiths (1997) and Weber (2000) recommend that the way to overcome the
problem is to never use a rearward facing restraint in the front seat of a vehicle
equipped with dual air bags and to encourage all pre-teen children ito use the
rear seat.
There is a potential problem in Australia with some styles of vehicle that do not
have a rear seat, such as utilities ("pick-ups") because dual airbags might soon
be introduced on these vehicles. However, the airbags used in Australia tend to
be less aggressive than those in the USA which, by regulation, must protect
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 51
unbelted occupants. This, combined with the firm restraint provided by a top
tether and 6-point harness, will probably mean there is no danger from airbags to
Australian children restrained in a forward facing child seat in such vehicles but
research is needed to confirm this premise.
Side airbags are also becoming more common in modern vehicles. Although
according to Weber (2000) less than 1% of these are in the rear seats. Weber
(2000) also reports that there have been no studies reported to date that children
properly restrained in child restraints of any type will be at any increased risk of
injury. However she does cite studies that have shown unrestrained children and
out of position children could be injured by these devices.
Despite the apparent lack of incidents, there is clearly a need for more research
into the interaction of CRS with side airbags
SUMMARY OF ISSUES
Australian experience with CRS
•
Australia has had more than 25 years of experience with top tethers on CRS.
In-depth crash studies, laboratory research and ongoing monitoring of serious
crashes involving children have demonstrated the wisdom of the main
features of Australian CRS: top tether, 6-point harness, single point of
harness adjustment and exclusive use in the rear seat.
•
The introduction of ISOFIX anchorages on many new vehicles provides an
opportunity to address recognised deficiencies in CRS: misuse of the adult
seat belts and inadequate restraint in side impacts. However, care will be
needed to ensure that Australian CRS designed for ISOFIX will also be able
to utilise the adult seat belts, where ISOFIX anchorages are not available.
This would apply with older vehicles or newer vehicles where the centre rear
seat is to be used.
•
Despite their proven effectiveness in many types of crashes there are still
improvements that can be made to Australian child restraints. These include:
•
Boosters with better sides for the sleeping child
•
Further development or addition of energy-absorbing side wings to all
child restraints to protect the head in the event of a side impact.
•
Tight fitting of the base of the child restraint to the car seat, either through
tensioned rear base straps or rigid base fittings. ISOFIX type fittings
should enable this to be readily achieved.
•
Visual indicator systems which indicate when the child restraint is correctly
fitted and all the straps are tensioned correctly.
•
Tighter restrictions on (regulated) zones for location of top tether
anchorages for child restraints.
•
More biofidelic child test dummies and validated injury criteria.
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 52
•
Encouraging carers to keep children under 12 months in rearward-facing
for as long as possible (recognising that rearward facing CRS are best for
very young children).
•
Improved protection for the 3-10 year olds. There is scope for improving
the level of protection available to those children through improved
booster design.
The Kinetics of CRS
•
Theoretical and modelling work confirms the soundness of the longestablished principle of restraining children in Australia - they should "ride
down" the crash with the vehicle and forward excursion should be minimised.
Forward excursion that is not associated with absorption of kinetic energy is
likely to be detrimental. This includes slack and elastic motion (ie with
rebound). Even forward excursion that involves absorption of energy could be
exposing the child to greater risk of injurious head contacts - this is of greater
concern than injuries from deceleration forces alone. Australian experience is
that children in forward facing child seats are not receiving serious injuries
from deceleration forces, even in very severe crashes.
•
A large range of laboratory tests of CRS have been conducted in Australia
since the early 1970s. These have given a better understanding of the
performance of CRS in real crashes and have contributed to the development
and improvement of standards.
•
In one series of crashes the same model of vehicle was subjected to
progressively higher speed impacts with a crash barrier, from 40km/h to
100km/h. A key finding was that the deceleration of the rear parcel shelf, to
which two CRFS were attached, tended to level off at speeds of 60km/h and
higher. As a result the loads on the child dummies did not increase
significantly at the higher speeds. Based on the child dummy injury
measurements, the 100km/h crash was considered to be survival because
the integrity of the rear occupant space was retained (unlike the front
occupant space).
•
At the current state of dummy development and knowledge about child injury
tolerances, it would be inappropriate, and quite likely counter-productive, to
base a CRS consumer rating program primarily on child dummy injury
measurements. The dummies lack biofidelity and links between dummy injury
measurements and risk of injury in real crashes has not been established.
This is the main reason Australian researchers have serious concerns with
the CRS assessment protocol proposed by EuroNCAP.
Effectiveness of CRS
• There are severe limitations in the use of mass crash data for assessing CRS
effectiveness. Such analyses can be quite misleading.
• In general all types of CRS have been demonstrated to provide higher levels
of protection for children than adult seat belts.
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 53
•
•
•
•
•
•
The absolute level of protection of a child restraint will depend on a number of
factors, including the type of restraint, its appropriateness for the child,
seating position, the vehicle characteristics and crash characteristics.
Rearward facing restraints have been shown to provide the highest level of
protection for children. Adult belt systems provide the lowest level of
protection for children but are still much better than no restraint.
The practice of restraining children in the rear seat means that Australian
child restraint effectiveness is likely to be higher than that reported for similar
types of restraint in comparable overseas studies where front seats are used
more often.
Child restraints will provide different levels of protection in different types of
impacts. Almost all studies have indicated that the rear seat provides more
protection than the front seat.
The effectiveness of child restraint has generally been found to be greater in
frontal impacts than side impacts and as, might be expected, more effective in
lower speed impacts than higher speed impacts.
There have been no rigorous estimates of effectiveness of Australian child
restraints. However it is likely that Australian child restraints are at least as
effective as their overseas counterparts.
Injury studies
Some of most important issues relevant to the effectiveness of child restraints
have been identified through in-depth crash investigations studying the injury
patterns of child occupants. In summary, these include the following.
•
Most injuries sustained by restrained children are minor in nature. The head
and the face are the most commonly injured region. The head is also the site
most frequently involved in serious and fatal injury to restrained children.
•
Head injuries in frontal impacts mainly occur via contact with the vehicle
interior.
In side impact, head injuries most commonly occur from either contact with
the vehicle interior and/or contact with the restraint.
•
•
Head injury is the most serious form of injury sustained by both children
restrained on the struck side and the non-struck side in side impact.
These issues suggest that in assessing the effectiveness of child occupant in the
laboratory, and in program aimed at improving the level of child occupant
protection, head protection should be the highest priority. In particular, limiting
head excursion in frontal impact and head contact stiffness in side impact are the
most crucial issues. Such findings confirm the experience of Australian
researchers in laboratory studies.
Also of importance are findings related to the risk of injury to other regions of the
body, These are summarised below.
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 54
•
•
•
•
•
Age related differences can usually be explained by the type of restraint being
used.
In rearward facing restraints it is uncommon for children to suffer injury to any
other region beside the head. In forward facing restraints the extremities, as
well as the head region are also injured more frequently than other body
regions but extremity injuries are usually fairly minor.
Most injury risk (as reported in statistical evaluations of restraint
effectiveness) is associated with the use of booster seats in conjunction with
adult seat belts. Along with high frequency of head injuries in children using
this form of restraint, the extremities, chest and the abdomen are also at
some risk.
Abdominal injuries are also common in children injured while using adult seat
belts, especially lap only belts. It is likely that these injuries (and those
suffered by children using boosters) occur from contact between the
abdomen and the belt system. Likewise, chest injuries occur frequently in
children injured while using adult belts.
Spinal injuries are also relatively common in children injured while using adult
seat belts. The region of the spine most commonly injured appears to be
different for different age groups of children. The cervical region being the
most common site in young children and the thoracic region being the most
common in older children.
The reports of misuse in a large proportion of the serious and fatal injury cases,
in a number of in-depth studies, is real cause for concern. Not all forms of misuse
carry the same risk. Further research is needed in this area.
Vehicle Factors
•
The current anchorage system used in Australia comprises two lower
anchorages formed by the existing seat belt and an upper anchorage using a
top tether. Lower anchorage geometry will depend on how the child restraint
has been designed in terms of seat belt routing and the actual geometry of
the lower seat belt anchorage. Top tether geometry also depends on the
restraint design, where the tether is mounted to the restraint and the location
of the anchorage point in the vehicle.
•
Anchorage system utilising top tethers have been found to be extremely
beneficial in reducing head excursion in frontal impacts.
•
Like other design features, it appears that there is some difference in how
well the top tether limits head excursion depending on design features of the
child restraint itself. The location of the anchorage point in the vehicle can
also influence performance. In particular problems with the anchorage point
being located too close to the seat back have been observed in Australia.
Anchorage that are not readily accessible or are likely to be contacted by
luggage are also a concern.
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 55
•
Field and laboratory studies have demonstrated that the current form of
anchorage employed in Australia is extremely effective in frontal impacts.
There is however scope to improve anchorage in terms of how well sideways
movement is controlled in side impact.
•
A new concept of anchorage has been developed and is beginning to be
introduced in many countries. This system makes use of rigid or semi rigid
lower anchorages and a means to limit pitch rotation of the child restraint
system. In North America and Canada authorities have adopted the rigid
lower anchorages (with rigid or flexible attachments) in conjunction with a top
tether. This concept has the potential to significantly reduce misuse and
restraint/vehicle incompatibility problems. It also has potential to significantly
improve the performance of child restraint systems in side impact.
•
The optimum performance of child restraints relies greatly on how tightly the
restraint is tied to the vehicle and how well the restraint ‘fits’ the vehicle.
Vehicle features related to how well these two criterion are met are therefore
have a bearing on how any particular restraint will perform in a specific
vehicle.
•
In terms of anchorages, the most important vehicle features are the location
of the top tether anchorage and characteristics of seat belt system. For the
seat belt system, the characteristics of particular importance include the
anchorage geometry of the belts, the length of webbing available, the
presence or not of seat belt enhancing technologies and the position of seat
belt buckles.
•
The ‘match’ between the general shape of the vehicle seat and any individual
child restraint can also influence the performance of the restraint, particularly
in terms of the restraint's stability. A poor ‘match’ could also exacerbate any
potential problems with seatbelt geometry. Characteristics of the seat also
have the potential to produce variations in the crash performance of any
individual child restraint compared to that observed in Standard tests. This is
mainly due differences between the actual vehicle seat (and seat anchorage
geometry) compared with ‘standard’ test seat.
•
Injury from the interaction of child restraint and airbags is unlikely to be a
problem in frontal impacts in Australia because almost all children will be
using restraints in the rear. The potential for injury from side impact air bags
in the rear is largely unknown.
CONCLUSIONS
The child restraint designs used in Australia have been shown to provide
exceptional protection to child occupants in severe crashes. Cases of serious
injury are likely to involve misuse of the child restraint or gross intrusion.
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 56
Lessons learnt
•
The number one priority in CRS design is to minimise excursion of the child's
head. To achieve this the child should be coupled as tightly as possible to the
structure of the vehicle.
•
Top tethers, in combination with an adult seat belt, are a very effective way to
firmly attach the CRS to the vehicle. Concerns about misuse (failure to attach
top tethers) are unfounded.
•
Six point harness distribute the crash forces to load-bearing parts of a child's
body and eliminate the risk of ejection.
•
No cases of serious neck injury to a child in a forward facing child seat with
top tether and six point harness have ever come to the attention of Australian
researchers, provided the CRS is correctly used and there is no gross
intrusion into the child's survival space. On the contrary, there been numerous
cases of children, some as young as 8 months old, surviving very severe
crashes without injury.
Still room for improvement
The following issues need to be addressed.
•
Injury measurements from the current generation of child dummies, when
used in forward facing CRS, should be treated with caution and should
certainly not be used as the primary means of rating performance of CRS.
Even if the biofidelity of child dummies is improved considerable more
research is needed in order to link such measurements with actual risk of
injury to children. Therefore child dummy injury measurements cannot be
used as a reliable indicator of real world performance.
•
Compatibility between vehicle and CRS needs greater attention. Top tether
anchorage location could be revised to improve dynamic performance,
improve accessibility and eliminate the potential for interference from
luggage. Seat back contours could be improved so that CRS fit better. A draft
assessment protocol has been developed by ANCAP for this purpose (see
Appendix).
•
Rear seat design in cars needs greater attention - for adults as well as
children..
•
CRS should provide much better head protection in side impacts. Large
"wings" with energy absorbing material would achieve this (also applies with
booster seats that are used in conjunction with adult seat belts).
•
The ease of use of various adjustments within CRS could be improved.
Retractable top tethers and harnesses would eliminate slack. Shoulder height
adjustment could be made simpler.
•
To minimise excursion of the lower part of the CRS, the routing of the adult
seat belt should be as low as possible.
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 57
•
Designs of CRS that can easily utilise either adult seat belts or ISOFIX
anchorages for lower restraint are needed, together with an education
program about the use of such CRS. Tell-tale device that confirm the CRS is
correctly installed should be considered.
Consumer test programs such as CREP and NCAP can provide incentive for
improvements to CRS design and compatibility between CRS and vehicles.
These programs also provide feedback for improvements to the Standard, by
giving an indication of those products that perform much better than the minimum
necessary to meet the Standard. However, at present, dummy injury
measurements should not be used as the primary method of assessment in CRS
evaluation programs.
There is an ongoing need to monitor crashes involving injury to children and to
conduct in-depth crash studies from time to time. CRS usage surveys also
provide feedback on CRS design problems and the need for educational
programs.
ACKNOWLEDGMENTS
Dr Michael Henderson and Paul Kelly provided advice for this project.
Much of the reported research on child restraints was conducted by Crashlab
(Roads and Traffic Authority of New South Wales) and its predecessor, the
Traffic Accident Research Unit (TARU).
In memory of Rodney Vaughan and David Herbert for their pioneering work at
TARU.
EFFECTIVENESS OF CHILD RESTRAINTS - THE AUSTRALIAN EXPERIENCE Page 58
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APPENDIX - Assessment of Child Restraint Installation and Use
DRAFT PREPARED FOR AUSTRALIAN NCAP, 2001
1. Introduction
This protocol sets out the procedures for testing and assessing the installation of
child restraints in vehicles and the ease of putting a child dummy into the
restraint.
This version applies only to child restraints that are suitable for children aged
from 12 months to 3 years. In Australia it applies to Type B (forward facing child
seat, Type A/B (convertible between rearward facing for infants and forward
facing for toddlers) and Type D (rearward facing for toddlers - none on the
market in Australia). It assumes that the child restraint:
• is provided with a top tether
• complies with the Australian Standard 1754 and
• is only installed in a rear seating position.
The Australian Standard has mandatory installation and ease of use
requirements and checks of these are not covered by this protocol. In effect, it is
a check of child restraint design features that go beyond the minimum set out in
the Australian Standard, together with checks of compatibility with the vehicle.
The test may be conducted with one child restraint that is moved between the
nearside and offside rear seating positions or with two child restraints in these
seating positions. The TNO P1.5 dummy is tested in the nearside seating
position and the TNO P3 dummy is tested in the offside seating position.
Only one person should carry out the installation, although others may observe
and assist with scoring.
A default score applies to most clauses. Also listed are reasons for reduced
scores - either half points or zero points. In some cases a bonus point can be
earned for favourable design features.
2. Test equipment
•
One or two child restraints as selected in accordance with the test protocol.
•
Two test dummies: TNO P1.5 and TNO P3.
•
Spring balance or similar device for measuring applied force
•
Tape measure
•
Device for measuring angle of inclination
•
Device for measuring yaw rotation of child restraint
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3. Preparation of vehicle
Front Seats
Both front seats should be adjusted to the test position specified in the
EuroNCAP test procedure for the offset frontal test.
If the seats need to be moved in order to install the child restraint this should be
noted (see clause XX).
Rear seats
If adjustable, the seat to be fitted with the child restraint should be adjusted so
that the seat back angle is 25o (+/-2o) from the vertical or to the angle specified
by the vehicle manufacturer, where this is clearly stated in user instructions.
If applicable, locate the top tether anchorage points and ISOFIX anchorage
points. Ensure appropriate fittings are available for the anchorages.
4. Installation of child restraint in vehicle
4.1 Installation instructions
Locate the installation instructions attached to the child restraint. Read and
assess the clarity of the installation instructions
(2 points)
Bonus point
(a) Video of installation
procedures provided
Half Points
(a) Instructions are
ambiguous or poorly
illustrated
Zero Points
(a) No installation
instructions provided on
child restraint
4.2 Installing child restraint
If the child restraint is reclinable set it to its most upright position [check AS, ECE
and EuroNCAP procedures].
Place the child restraint on the vehicle seat. Following the fitting instructions,
pass the adult seat belt through or around the child restraint. Buckle up the seat
belt and remove any slack. Note the ease of doing this and the likelihood and
consequences of misuse.
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Page A2
(4 points)
Bonus point
Half Points
(a) Correct path is clearly
(a) Difficult to feed the seat
colour coded (dual colour
belt through the correct
system used for
path
convertible restraints)
(b) Child restraint needs to
be moved or rotated
substantially to gain
access to path
(c) Seat belt buckle difficult
to do up due to its
location or interference
from CR components
Zero Points
(a) Possible to incorrectly
feed the seat belt so that
it fails to provide restraint
(but looks correct).
(b) Seat belt buckle strap
not under tension when
tongue is latched
(insufficient distance
provided between
anchorage and child
restraint)
(d) Child restraint does not
mate with the geometry
of the seat so that there
could be confusion about
the correct installation
position
If applicable, apply and adjust any seat belt locking device associated with the
child restraint. Note the ease of doing this and the likelihood and consequences
of misuse.
(1 point if a guide/device is not required or the locking device is provided as an
integral part of the child restraint. (Gated buckles are not eligible))
Bonus point
(a) -
Half Points
(a) Guide/device provided
but if not used is unlikely
to compromise security
of child restraint
Zero Points
(a) Guide/device provided
and, if not used, is likely
to compromise security
of child restraint
Connect the top tether strap to the appropriate anchorage fitting. If necessary
use an extension strap. Note the ease of doing this and the likelihood and
consequences of misuse or inappropriate use, including:
•
having to fold-down a seat or seats behind the seating position in which the
child restraint is installed in order to access the anchor fitting;
•
the incorrect use of alternative anchorage points (such as those for a third
row of seats):
•
the risk of the top tether slipping between split seats.
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Page A3
•
whether it was necessary for the installer to move to a different position to
attach the top tether, including moving outside to open the rear hatch.
(4 points)
Bonus point
(a) -
Half Points
Zero Points
(a) Installer needs to move
to a different part of the
vehicle in order to attach
the top tether.
(a) Having to fold-down a
seat or seats behind the
seating position in which
the child restraint is
installed in order to
(b) Extension strap required*
access the anchor fitting.
(c) Difficult to clip tether into
anchorage due to limited (b) A child restraint
anchorage for another
access, proximity of
seat might be confused
objects or angle of attack
for the correct one
(where the other
anchorage does not
comply with location
requirements).
(c) Tether strap likely to slip
between split seats or
another location that will
compromise security of
restraint.
* Note: If top tether is required but cannot be attached, even with an extension
strap, then assess the location of the anchorage point against the relevant ADR.
If non-compliance is established, then the assessment should be abandoned.
Adjust the top tether so that it is firm. Note the ease of doing this. Note whether
the child restraint tends to tilt backwards so that the front lifts off the seat
cushion.
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Page A4
(2 points)
Bonus point
(a) -
Half Points
Zero Points
(a) A force of more than 50N
is required to move the
webbing through the
adjuster, once static
friction has been
overcome, or awkward
manual manipulation is
needed to adjust top
tether.
(b) When top tether is
tightened firmly the front
of the child restraint lifts
substantially off the seat
cushion (gap more than
60mm) so that the
installer may be tempted
to loosen the tether.
(a) Top tether runs out of
adjustment before it is
tight.
(b) With the top tether firmly
tightened the child
restraint tilts back
excessively (seat back
angle more than 35o from
the vertical for forward
facing restraints or less
than 15o for rearward
facing restraints)
(c) The top tether anchorage
clip is loaded in bending
because it fouls a
component and is unable
to align with the webbing.
Observe whether the top tether is likely to be in the way of luggage or rearward
passengers. For this purpose "luggage" may regarded as a 400mm cube placed
anywhere on the floor of the cargo area.
(2 points if no obstruction)
Bonus point
1. -
Half Points
Zero Points
(a) The top tether or
extension strap passes
through the sitting space
of an occupant to the
rear (where that seat is a
fold down seat that is not
normally used)
(a) The top tether or extension
strap passes through the
sitting space of an occupant
to the rear (permanent seats
only) or interferes with
access to a seat.
(b) The top tether or
extension strap passes
through the luggage
space and would be in
the way of luggage (less
than 400mm above
cargo space floor at any
point)
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(b) The top tether or extension
strap is vulnerable to
damage from unsecured
luggage in the event of a
crash (webbing is in the
forward part of the cargo
space and is unprotected
between the floor and
400mm above the floor).
Page A5
For the portion of the top tether rearward of the seat top or the CR (whichever the
top tether last contacts) measure the angle extended rearward [diagram excessive angle introduces slack].
Bonus point
(a) -
Half Points
Zero Points
(a) For a roof mounting, the
angle of the top tether is
between 300 and 450
above the horizontal
(a) For a roof mounting, the
angle of the top tether is
more than 450 above the
horizontal
For the portion of the top tether between its point of attachment to the child
restraint and the seat top, measure the angle from the horizontal with the child
restraint in its installed position [diagram - excessive angle introduces slack].
(4 points)
Bonus point
(a) -
Half Points
(a) Angle is between 30
and 45o.
Zero Points
o
(a) Angle is more than 45o.
Determine the first sturdy point of contact between the lap portion of the adult
seat belt and the lower part of the child restraint (the effective lower attachment
point). Measure the angle from the horizontal of a line between this point and the
seat belt anchorage point [excessive angle introduces too much slack into lower
part of child restraint]. If there is a large deflection of the webbing due to the seat
cushion, note the increase in seat belt length that would result were the cushion
not present. [diagram - including estimation belt lengthening]. If the geometry on
either side is not symmetrical then measure the angle on both sides and use the
worst case. If there is more than one path for the seat belt use the worst case.
For rigid ISOFIX systems assume the angle is zero degrees.
(4 points)
Bonus point
(a) The child restraint
provides for rigid
attachment to an ISOFIX
style anchorage
(b) The child restraint
provides for flexible
attachment to an ISOFIX
style anchorage and the
length of the attachments
adjusts automatically.
Half Points
(a) Angle is
between 45o
and 60o
Zero Points
(a) Seat belt angle is more than 60o or
is rearwards (seat belt anchorage
point is forward of point of
attachment to child restraint)
(b) Belt lengthening due to cushion or
other non-structural component is
more than 50mm.
(c) The seat belt passes through slots in
the back of the child restraint that
have a opening with a gap larger
than 50mm in a vertical direction
(not applicable if there is a device to
prevent the webbing sliding out of
position).
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Page A6
4.3 Measuring slack, under steady load, between child restraint and vehicle
Measure yaw rotation in either direction when a lateral force of 100kN is applied
to the foremost structural point of the child restraint. Use the largest angle for
assessment [diagram - reduce rotation of child restraint in side impacts]
(1 point)
Bonus point
Half Points
(a) Angle is between 20o
and 30o
(a)
Zero Points
(a) Angle is more than 30o.
5. Child Restraint Use - Checks with dummy in child restraint
5.1 Preparation of child restraint
Read and assess the clarity of usage instructions.
(2 points)
Bonus point
(b) Video of installation
procedures provided
Half Points
Zero Points
(b) Instructions are
ambiguous or poorly
illustrated
(b) No instructions for adjusting
harnesses to suit the child are
provided on child restraint
Briefly place the child restraint on the vehicle seat and the dummy in the child
seat - do not attach tethers, adult seat belts or harnesses at this stage.
Determine the appropriate harness slot height (in accordance with the child
restraint instructions or otherwise, where possible, the lowest position that is
above shoulder height).
Remove the dummy and child restraint from the vehicle.
Relocate the shoulder straps to the shoulder strap slots as determined in Section
5.1.2. Note the ease of adjustment of harness slot height and the likelihood of
serious misuse
(2 points)
Bonus point
(a) Height can be readily
adjusted without
removing webbing or
disassembling any
component (height
adjusting device
provided).
Half Points
(a) Adjustment method is
straightforward but
tedious so that users
may but reluctant to
adjust harness.
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Zero Points
(a) High risk of incorrectly
reassembling harness
after changing slot
height.
Page A7
Adjust harness to its maximum length. Note the ease of lengthening the harness.
(1 point)
Bonus point
(a) -
Half Points
(a) -
Zero Points
a) between 50N and 75N
force needed to lengthen
harness.
b) Harness can only be
lengthened by
manipulating it in some
way other than by pulling
on the shoulder straps.
If the child restraint is fitted with a crotch strap or leg straps that have fore and aft
positions, determine the ease or difficulty with which the positions can be
changed.
(1 point - in effect, a bonus for having adjustable straps)
Bonus point
(a)
Half Points
(a) Adjustment method is
straightforward but
tedious so that users
may but reluctant to
adjust the straps.
Zero Points
(a) Easy to incorrectly
reassemble straps after
changing repositioning
them.
5.2 Placing dummy in restraint
If necessary, disconnect the top tether and note the ease of doing this
(1point if top tether does not need to be disconnected).
Bonus point
(a)
Half Points
(a) Top tether can be
disconnected without
unclipping it from the
anchor fitting (quick
release buckle is
provided)
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Zero Points
(a) Top tether needs to be
detached from the
anchor fitting.
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Place the dummy in the child restraint. Place the harness on the dummy and
secure the buckle. Note the ease of doing this and the likelihood and
consequences of misuse. Note that the harness should still be at its maximum
length in accordance with clause 5.1.5.
(4 points)
Bonus point
(a)
Half Points
(a) Dummy limbs need to be
placed in an awkward
position in order to fit
harness (this may be due
to insufficient spare
length in the harness
straps).
Zero Points
Difficult to engage the
tongues in the buckle.
(e.g. buckle design
requires both tongues to
be manipulated to obtain
a specific configuration
before inserting them
simultaneously into the
buckle.)
(a) Potential for buckle to be
incorrectly latched
If necessary, adjust the harness to remove slack. Note the ease of doing this and
the likelihood and consequences of misuse.
(4 points)
Bonus point
(a) Harness is designed to
adjust automatically and
works as intended.
Half Points
(a) -
Zero Points
(a) A force of more than 50N
is needed to adjust the
harness, once static
friction has been
overcome.
Observe whether the shoulder straps are likely to slip off the shoulders or rub the
neck of the dummy [diagram].
(2 points)
Bonus point
(a) Lateral adjustment of
shoulder slots available
and simple to operate.
Half Points
Zero Points
(a) Harness shoulder straps
rub the neck of the
dummy.
(a) Harness shoulder straps
are likely to slip off the
shoulders of the dummy
(the centreline of the
webbing is further
outboard than the midpoint of the dummy's
shoulder).
If necessary, reconnect the top tether (no assessment).
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Page A9
5.3 Checking clearance within vehicle
Forward facing restraints (see 5.3.2 for rearward facing). Measure the horizontal
distance from the child restraint harness buckle to the rear surface of the seat in
front (or other object, if applicable). [diagram - note front seat at mid-point of
travel]
(4 points)
2 Bonus points
(a) -With the front seat in its
rearmost position the
clearance is at least
700mm
Half Points
(a) Clearance is between
550mm and 700mm
Zero Points
(a) Clearance is less than
550mm or part of the
dummy touches the seat
Rearward facing restraints. With the front seats in the position specified in
Section 3.1, note whether there is sufficient space between the front and rear
seats to install the child restraint. [diagram - note front seat at mid-point of travel]
(4 points)
2 Bonus points
Half Points
Zero Points
c) With the front seat in its
(a) The child restraint can be (a) Child restraint cannot be
rearmost position there is
installed, but touches the
accommodated.
room for the child
back of the front seat
restraint (no contact
between seat and child
restraint).
Check if the dummy’s face be seen by the driver (either by turning around,
looking in a mirror or looking at a visual aid)
(2 points)
Bonus point
(a) A visual aid, such as a
camera and monitor, is
provided
Half Points
(a) The driver needs to turn
around in order to see
the face of the dummy
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Zero Points
(a) The dummy’s face
cannot be seen by the
driver
Page A10
5.4 Removing dummy from child restraint
If necessary, disconnect the top tether (see next clause).
Undo the harness buckle. Release the dummy from the harness straps and
remove the dummy from the child restraint. Note the ease of doing this.
(2 points)
Bonus point
(a) In an emergency the
child restraint, together
with occupant, can be
quickly removed from the
vehicle. (check the
effectiveness of such a
facility)
Half Points
(a) More than one hand is
needed to release the
harness
1. Dummy limbs need to be
placed in an awkward
position in order to
remove harness.
Zero Points
(a) It is necessary to undo
the top tether in order to
remove the dummy from
the restraint but no quick
release device is
available.
2. It is necessary to undo
the top tether in order to
remove the dummy but a
quick release device
available so the top tether
does not need to be
unclipped from the anchor
fitting.
Disconnect the child restraint and remove it from the vehicle. Note the ease of
doing this.
(1 point)
Bonus point
(a) -
Half Points
(a) Installer needs to move
to a different part of the
vehicle in order to
remove the child
restraint.
Zero Points
(a) Potential for child
restraint to be
disassembled during
removal from vehicle.
(b) Difficult to remove adult
seat belt from child
restraint.
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6. Maintenance of child restraint
Follow manufacturer's instructions for removing covers, inserts and other
washable items from the child restraint. Reassemble the components.
(2 points)
Bonus point
(a) -
Half Points
(a) Difficult to remove or
reassemble washable
items
Zero Points
(a) Potential for incorrect
reassembly of child
restraint after cleaning.
(b) Poor instructions.
7. Calculation of score
For each clause in sections 4 to 6, take the worst score (that is, zero points, half
points, full points or full points plus bonus).
Add the resulting scores for each clause to obtain a total score for the child
restraint installation. The maximum score is XX points, irrespective of bonus
points scored.
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