Passenger Cars and Occupant Injury

Federal Office of Road Safety - Contract Report 95

Full report in .pdf format [10MB]

Abstract:

This project was undertaken to evaluate the level of protection afforded occupants of current generation passenger cars available on the Australian market and to provide directions for future improvements in occupant protection. A literature review was initially undertaken to highlight reported vehicle occupant injuries and sources of injury as well as countermeasures which are presently under consideration overseas. A mass database was constructed of injury compensation data at the Transport Accident Commission in Victoria, supplemented with police and some make/model information, for detailed analysis. In addition, a program was undertaken of detailed inspections of 227 crashed vehicles where at least one occupant was hospitalised to provide details on sources of injury from current generation vehicles involved in road crashes. This first report describes the findings to date and makes recommendations on a range of suitable countermeasures to reduce the incidence and severity of injuries for front seat occupants involved in frontal crashes. A supplementary volume provides a case by case summary of each of the crashed vehicles inspected. Further reports are planned to provide recommendations for other seating positions and crash configurations when additional data becomes available.

Executive Summary

INTRODUCTION

New passenger cars sold in Australia have been required to meet vehicle safety standards specified in Australian Design Rules for Motor Vehicles and Trailers (ADRS) since 1970. For the most part, these ADRs aim to "harmonize" with similar vehicle safety standards in Europe and the USA.

Recent changes in vehicle construction, a trend towards smaller vehicles on our roads, and the effects of high levels of seat belt wearing need to be evaluated in terms of occupant protection for passenger car occupants involved in vehicle crashes. This report examines the current level of occupant protection of current generation passenger cars in Australia.

THE AIMS OF THE STUDY

The study was undertaken for the Federal Office of Road Safety by the Monash University Accident Research Centre to provide a focus for the future development of occupant protection improvements in Australian passenger cars and their derivatives. The research was in three parts:

1. First, a review of the international safety literature was undertaken to provide a background of the types of injuries being sustained by vehicle occupants, the sources of these injuries within the vehicle, and international developments in occupant protection.

2. Second, a detailed analysis was carried out of seven and one-half years of Transport Accident Commission (TAC) injury compensation data involving recent vehicle occupants, supplemented with police accident report details, to obtain an overview of the pattern of injuries to occupants of modern passenger cars in this country.

3. Finally, a "follow-up" study was performed of 227 passenger car crashes in and around Melbourne where at least one occupant of a modern passenger car was hospitalised from the crash (total of 269 patients). This investigation involved an examination of patients and their vehicles to link occupant injuries with sources of injury inside the vehicle for various types and seventies of crashes.

All this information was then drawn together to provide a picture of the types of injuries sustained by occupants of modern passenger cars, particular design and component problems, and potential solutions for Australian vehicles.

This first stage report focuses principally on front seat occupants involved in frontal crashes. Recommendations are made about a range of potential countermeasures for these occupants, along with further research and development work required. Future reports are planned to provide recommendations for other crash configurations and seating positions when additional data from a larger number of crashes has been collected.

A supplementary volume is also available which provides a case by case summary of each crashed vehicle inspected.

THE EXTENT OF THE PROBLEM

From the mass data analysed and the crashed vehicles inspected, this study was able to provide an overview of the types of vehicle crashes that occur and the nature of injuries sustained by occupants of current generation vehicles.

TYPES OF CRASHES - Amongst TAC claimants, frontal impacts were most prevalent (47%), followed by side collisions (25%), rear enders (23%) and rollovers (5%). Rear end crashes were considerably under-represented in terms of severe injuries compared to all other crash configurations. These figures are roughly equivalent to those reported in other countries and illustrate the higher and lower likelihood of severe injury requiring hospitalisation for these particular crash configurations.

One-third of frontal impacts in the crashed vehicle sample were pure frontals (central and longitudinal), another third were pure offsets (longitudinal offset), while the remaining third of frontal crashes were oblique offset collisions. These figures are also similar to other reports in the literature.

Roughly half the number of front seat occupants in the crashed vehicle study were hospitalised from frontal crashes where the estimated impact velocity change (delta-V) was less than 48kni/h. (This value represents the impact speed for barrier crash testing for pure frontals where belted occupants would expect to be protected from these crashes).

SEATING POSITIONS - Injured occupants were most frequently drivers (63%) or front seat passengers (24%), rather than rear seat occupants (13%) in these state-wide data. This probably reflects the frequency with which these seating positions are occupied in vehicles on the road, but may also indicate slight differences in injury susceptibility across these different seating positions.

Drivers sustained slightly more injuries than other occupants among the total crashed vehicle sample. However, there were roughly equal numbers of severe injuries to hospitalised occupants in all seating positions.

VEHICLE MASS - Mini cars (under 750kg) were over-involved in low speed zone crashes amongst TAC claimants, while intermediate (1250-1500kg) and large cars (more than 1500kg) were over-involved in high speed zone crashes. Mini and small cars were also associated with more severe injuries, often involving very young and very old (predominantly female) occupants from urban crashes.

It was not possible to compare vehicle involvement or injury severity rates by the different vehicle makes and models in this study.

VEHICLE INTEGRITY - Structural deformations and intrusions were quite frequent amongst the frontal crashed vehicles examined in the follow-up study. The toe pan, instrument panel, steering assembly, side panel, A-pillar and console were common sources of intrusions in the front seating areas.

Rear-wheel drive compact cars (1000-1250 kg) appeared to sustain more intrusions (including longitudinal movements of the steering column) than did front-wheel drive compact vehicles.

Steering assembly intrusions were also quite common in frontal crashes, especially those involving lateral and vertical movement. However, there were very few instances of longitudinal intrusions beyond 127mm for impact speeds of 48km/h or less, as specified by Australian Design Rule ADR 10/01.

TYPE OF OCCUPANTS - Older occupants (those aged 55 years or more) were more likely to be severely injured than younger occupants in all seating positions. Males, too, were over-represented in severe injury claims at the TAC, which is likely to be related to their over-involvement as drivers, non-wearers of seat belts, and being involved in high speed zone crashes.

SEAT BELT WEARING - Seventeen percent of hospitalised front scat occupants in the crashed vehicle study were not wearing seat belts compared with a 6 percent non-wearing rate in the population at large. This illustrates the protective nature of these restraints, although it may also indicate that unrestrained occupants are over-involved in crashes.

Seat belts did not appear to influence the number of entrapments for front seat occupants in frontal crashes. However, they were of substantial benefit in preventing ejections from the vehicle during frontal crashes.

Data on scat belt wearing behaviour in the mass data was not reliable because of artificially high rates of wearing reported by the police. However, unrestrained occupants may have experienced more severe injuries than restrained occupants for a given collision speed.

STATE-WIDE INJURY PATTERNS

The analysis of seven and one-half years of TAC vehicle occupant claims provided clear evidence of the types of injuries sustained by occupants of modern cars involved in crashes for different outcome severities.

There was a high rate of head, chest, abdomen and lower limb injuries amongst those who were killed or hospitalised for more than 6 days. Lower leg, minor head and face, and whiplash injuries were more prominent amongst occupants who were hospitalised for short periods as well as those requiring only outpatient treatment resulting from a vehicle crash.

Head injuries were more common (and chest and abdomen injuries less frequent) amongst occupants severely injured from rear end and rollover collisions than from front or side collisions. For less severe outcomes, chest and lower limb injuries were more common among occupants from front and side impacts than rear enders or rollovers.

Severe spinal fractures were more frequent amongst those injured in rollover, rear end and side than frontal crashes. Front and rear centre seat occupants were especially vulnerable to severe head and spine injuries compared to those in outboard seating positions.

There was also a suggestion in these data that drivers and front left passengers suffered more head and chest injuries than rear seat passengers in severe collisions. In addition, lower limb injuries were more prevalent in the front than the rear seats.

Occupants in mini and small cars tended to have slightly more severe head and chest injuries than occupants of larger cars, even though these small vehicles were predominantly involved in lower speed urban crashes.

CRASHED VEHICLE STUDY INJURIES

The crashed vehicle study results were in general agreement with these state-wide injury patterns and were able to provide a more comprehensive account of front seat occupant injuries (including injury severity) from frontal crashes for a limited number of crashes. It was not possible, though, to highlight differences in injury types and seventies between pure and offset frontal crash injuries at this stage.

Drivers sustained more body region injuries (including more severe injuries) than front-left passengers in frontal crashes and their average injury severity score (ISS) was higher.

Drivers in frontal crashes experienced a sizeable number of severe injuries to the abdomen, chest, and the upper and lower extremities. Front seat passengers also had similar injuries except for fewer severe chest injuries. There were a number of severe head injuries to injured occupants in both front seat positions.

Because of the requirement for hospital entry into the study, it was not possible to evaluate the effectiveness of seat belts in preventing injury. Nevertheless, there were subtle differences in the pattern of injury between belted and unbelted front seat occupants, where unbelted front seat passengers in particular sustained fewer severe chest, but more upper limb, pelvic, and lower limb injuries than their belted counterparts.

SOURCES OF INJURY INSIDE THE VEHICLE

The crashed vehicle study was the only source of information regarding which vehicle parts were associated with injuries in local vehicles. (While overseas information from the literature was also of interest here, it was not directly comparable because of differences in the types of vehicles and seat belt wearing rates).

The three most frequent sources of injury for drivers in frontal crashes were the steering wheel, instrument panel, and seat belts. The most common severe injury/source contacts for drivers in frontal crashes were the chest with the steering wheel, lower legs with the floor, head with the steering wheel, thigh or knee with the instrument panel, and chest with the belt.

For front left passengers, the instrument panel, seat belts, and the windscreen or header were primarily involved in their injuries. For these passengers, the most frequent severe injury and source contacts included the upper limbs with the instrument panel, the chest with the seat belt, the thigh or knee with the instrument panel, and lower leg with the floor.

Apart from the steering assembly for drivers, there were very few differences in the patterns of injuries and contact points for these front seat occupants in frontal crashes.

Again, it should be stressed that these results cannot be used to assess the overall effectiveness of the seat belt for reasons previously stated. However, there were observable differences in the pattern of contacts between belted and unbelted front seat occupants.

Unbelted front seat occupants experienced more head, face, and upper limb injuries from contact with the windscreen and header and exterior objects. Belted occupants experienced more chest and abdominal injuries, essentially from contact with the seat belt. Driver contacts with the steering wheel and instrument panel were quite common irrespective of whether they were belted or not.

Similarly, unbelted front seat passengers had more windscreen and exterior contacts, as well as more severe injuries from the instrument panel and windscreen, than their belted counterparts.

FRONTAL IMPACT COUNTERMEASURES

The three-point restraint system continues to be the main countermeasure against occupant injury for front seat occupants in frontal crashes. Current concern needs to be with increasing the protective effect of the system and reducing injuries shown to be associated with belt use.

The following list of potential countermeasures is suggested from this research program. It should be noted that further research may be required to demonstrate the cost effectiveness of some of these measures.

STEERING WHEELS - Steering wheels and hub contacts are still a major source of injury to drivers involved in frontal crashes. A padded and more forgiving steering wheel has been developed overseas to alleviate these injuries and one or two European vehicles now offer such a device as standard equipment. This study demonstrates the need for similar improvements in Australian vehicles.

IMPROVED RESTRAINT SYSTEMS - Restraint systems have been remarkably successful in reducing injuries to front seat occupants in frontal crashes. This study shows that there is still scope for further improvements to restraint systems. In particular, total seat belt extension should be reduced to minimize contact injuries while belt geometry needs improving to reduce submarining and other injuries. Attaching the belt anchorage points to the seat, D-ring adjustment, pre-tensioners or webbing clamps, and perhaps stiffer webbing or wider seat belts are all possible improvements to reduce the severity of these injuries.

SUPPLEMENTARY AIRBAGS - A further benefit for front seat occupants involved in frontal crashes could be derived from fitting airbags to supplement existing 3-point belt restraint systems. They would help reduce contacts with the steering wheel for drivers (and dashboard area for front seat passengers), cushion these impacts, and help reduce seat belt loadings. In addition, full size airbags would improved protection in frontal crashes for unrestrained front seat occupants.

Further evaluation is necessary at this time to establish the cost effectiveness of airbags as a secondary unit, bearing in mind the possible improvements in outcome from other additions such as padded steering wheels and belt tensioners and clamps. In the meantime, however, manufacturers should be encouraged to make these units available as an option for Australian models which have an equivalent model overseas with airbags fitted as standard equipment.

STEERING COLUMN MOVEMENT - ADR10/01 specifies acceptable longitudinal steering column movement requirements for vehicles involved in a frontal barrier crash. However, there is no specification of acceptable lateral and vertical column movements. As there were many instances of severe injury from contact with the wheel and column which could be directly attributed to movement in these two additional planes, it would be desirable to include acceptable levels of lateral and vertical, as well as longitudinal movements, in this standard.

INSTRUMENT PANEL - There were numerous instances of severe contacts between front seat occupants and the instrument panel in frontal crashes, involving both the upper and lower surfaces. Intrusions into occupant spaces that resulted in occupant injury need to be reduced as a matter of priority.

Furthermore, plastic materials used in these structures were aiding injury by shattering into sharp jagged segments, and lower attachments (radio components, switches, fuses, etc.) were targets for forward moving body components such as knees and lower limbs.

There is considerable scope for better padding, sheet metal rather than rigid plastic structures, and no protrusions to minimize these injuries. The safety consequences of flimsy lower parcel shelves also need to be addressed.

KNEE BOLSTERS - Reduced contacts with the lower instrument panel and minimizing the effects of submarining have been achieved overseas by fitting knee bolsters to cars at knee height and in front of the lower instrument panel across the full width of the vehicle. On the evidence collected here, these devices would seem to be applicable for Australian vehicles as well.

WINDSCREENS & HEADER SURFACES - Even with the high rates of seat belt wearing in Australian vehicles, front seat occupants (notably passengers) had frequent contacts with the windscreen and header surfaces. In addition, A-pillars were also involved in many contacts, albeit at a lesser rate.

This suggests the need for additional interior padding on these support surfaces to cushion these impacts, for plastic laminates on the interior of windscreens to reduce the instances of lacerations, and for structural improvements to minimise pillar and header rail intrusions. The safety consequences of low rake angles in some vehicles also needs to be assessed further.

FLOOR & TOE PAN - The floor and toe pan of the vehicle was associated with injury to front seat occupants in frontal crashes in 25 percent of cases, with intrusions in only 7 percent of cases. These injuries could be alleviated to some degree by better restraint systems, improved seat design, and possibly knee bolsters to prevent downward jarring injuries and submarining.

However, improved vehicle design of the floor and toe pan area and their associated structures to minimize the number and severity of intrusions would also be advantageous here. The possibility of structural changes to reduce the frequency or extent of front wheel intrusions should also be investigated.

BARRIER CRASH TEST - Some of the suggested improvements detailed above could be achieved if cars were required to meet the performance requirements of the frontal barrier crash test in FMVSS 208 (without the passive restraint requirement, ie., allowing the seat belt to be fastened manually). This standard assesses the vehicle performance based on injury criteria measured on an instrumented dummy during a crash test.

While there is some criticism of the fact that FNWSS 208 does not include an offset configuration, nevertheless, it could be argued that this existing full frontal crash requirement is better than no standard at all. Naturally, any consideration of an Australian equivalent should also address the matter of full versus offset frontal configurations and whether 48km/h is a suitable impact speed for crash protection in the longer term.