Vehicle Occupant Protection: Four-wheel-drives, utilities and vans

Federal Office of Road Safety - Contract Report 150

Full report in .pdf format [4MB]

Abstract:

Although the number of 4WDs, utilities (not passenger car derivatives) and forward control vans in Australia is increasing, very little is known about the occupant protection they offer in real world crashes. Furthermore, these vehicles are not subject to the full range of design rules applicable to passenger cars and their derivatives. The aim of this study was to examine the extent and patterns of injuries sustained by occupants of 4WDs, utilities and vans in crashes where the vehicle was classified as "written-off", and to ascertain the need for more stringent regulations governing this group of vehicles. The study involved three main stages: (1) a review of the international literature covering the crash types and crash performance associated with these vehicles (or their closest overseas equivalents); (2) analysis of two mass databases covering casualty crashes in NSW and fatal crashes throughout Australia where vehicle type was coded; and (3) a detailed investigation of 144 "write-off" crashes involving roughly equal numbers of post-1985 4WDs, utilities and vans.

The majority of crashes were found to be frontal ones, although rollovers were over-represented (mainly for 4WDs) by comparison with the crashed passenger car file. The crashes sampled in this study were of low severity compared to the sample of passenger car crashes, as reflected by relatively low impact velocities (modal Delta-V of 18-24 km/h), few instances of entrapment or ejection, and low levels of injury (84% either uninjured or minor injury not requiring hospitalisation). Minor (AIS<2) injuries to the upper limbs through contact with seat belts, steering wheels and instrument panels were most common, although whiplash injuries were also prevalent (approximately one-third of all drivers). Injuries to the upper and lower leg through contact with the instrument panel and floor were over-represented among van drivers, consistent with the preponderance of frontal crashes and the reduced crumple space in these vehicles. Head and spinal injuries caused by roof contacts were slightly over-represented among drivers of 4WDs and utilities, consistent with their over-involvement in rollover crashes. Countermeasures relating primarily to improved steering assembly, restraint systems and instrument panel construction are discussed and recommendations are made for an extension of the study to include more hospitalised cases.

Executive Summary

Four-Wheel-Drives, Cab-Chassis Utilities, and to a lesser extent, Vans, are becoming an increasing proportion of the vehicle fleet as many people choose to drive these vehicles as an alternative to passenger cars. In 1992, for instance, sales of 4WDs and Utilities represented 18.1% of all new vehicle sales, compared with 16.7% in 1991.

While a number of current Australian Design Rules apply to these vehicles (such as ADR 10/01 for steering column intrusions), these vehicles are not classified as "passenger cars or derivatives", and hence are not subject to the full range of design rules that currently apply to passenger cars in this country.

AIMS & STUDY TASKS

The objectives of this study were to examine the extent and patterns of injuries occurring to occupants of these vehicles and the need for more stringent regulations for this growing fleet of alternative passenger vehicles.

Three tasks were undertaken to meet these aims. First, a review of mainstream occupant protection literature was conducted to highlight previous published findings in this area.

Second, an analysis of six years of New South Wales tow-away casualty data and two years fatality data on the national fatal file was then carried out to illustrate the extent of the problem and patterns of injuries sustained by seriously injured occupants of passenger cars, four-wheel-drives (4WDs), vans and light trucks/utilities.

Finally, a thorough examination of 140 vehicles (4WDs, Vans & Utilities) which had been written-off as a result of a road crash with another vehicle or a fixed object was undertaken to provide a more detailed picture of the extent of damage, the injuries sustained by the occupants and the sources of these injuries from within or outside the vehicle.

MASS DATA ANALYSIS

The main findings from the mass data analysis of casualty and fatal crash data were as follows:

• Four-wheel-drives, utilities and vans involved in casualty crashes in NSW over the years 1987-1992 accounted for roughly 10% of road trauma to vehicle occupants.
• Four-Wheel-Drives, compared with other vehicle types, were over-involved in casualty and fatal crashes occurring in high speed zones (>75km/h), but were particularly over-involved in rollover crash configurations in both high and low speed zones.
• Rollover crash configurations were 12 times more likely to occur in high than low speed zones, and high speed zone rollovers accounted for 80% of injuries sustained in rollover crashes.
• While there were no consistent differences in overall injury severity between the vehicle types, 4WD occupants were marginally more likely to die in a high or low speed rollover crash than car or van occupants in equivalent crashes.
• Drivers of 4WDs involved in casualty or fatal crashes were more likely to be male and aged between 26 and 55 years; additionally, occupants of 4WDs were more likely than other vehicle occupants to be unrestrained and hence ejected.
• Passenger vans were over-involved in fatal outcomes in head-on crashes in low speed zones (< 75km/h) and their occupants were more likely to be trapped in the vehicle in these crashes. This is probably because of the more limited crumple space available in passenger vans.
• Head and chest injuries were the predominant cause of death in fatal crashes.
• Occupants of 4WDs killed in rollover crashes were slightly more likely to sustain a severe spinal injury but less likely to sustain a severe chest injury by comparison with passenger car occupants in equivalent crashes.

CRASHED VEHICLE STUDY

The pattern of crash types in the crash vehicle file mirrored those from the mass databases with 4WDs being over-involved in rollovers-nearly half of the 4WD crashes were rollovers. The mean delta-V value for 4WD crashes (35.5km/h) was lower than that observed in the crashed passenger car study (45.4 km/h) suggesting that these crashes were of relatively low severity, probably due to the vehicle-based entrance criteria. Observed belt-wearing rates were extremely high among this sample of relatively minor crashes (98%) and no occupants were ejected.

The vehicle-based entrance criteria and the relatively small number of cases (1 44) probably also contributed to sparse injury data and the low levels of injury severity observed (84% minor or no injuries). Further, the high number of "driver-only" vans and utilities in the sample resulted in very small numbers of occupants in other seating positions. The lack of major injuries and the small number of front-left and rear passengers in particular were problematic for this study. Nevertheless, some interesting trends were apparent in the data for drivers, and these are presented below.

Upper limb injuries were the most common injury among drivers of 4WDs, vans and utilities alike, but were relatively minor (only 2% or less with AIS > 2). These injuries were most often caused by contact with scat belts, the steering wheel and the instrument panel. Injuries to the thigh, knee and lower leg were also quite common, particularly among van drivers, and usually the result of instrument panel or floor contacts

Non-severe neck injures, mainly whiplash, were a notable feature of the injury pattern, with about one quarter of the drivers in each vehicle category sustaining one of these injuries. Whiplash injuries were typically from crash forces or were seat belt induced. Most of the head and chest injuries observed here were relatively minor, caused by contact with the steering wheel, side glazing, door panel or the roof.

Serious injuries, although a rare occurrence, were more prevalent among van drivers, particularly by comparison with 4WD drivers, only one of whom sustained a serious injury (AIS > 2).

Extremely small numbers prevented an analysis of injuries and injury sources for unrestrained, ejected, or trapped occupants.

POTENTIAL COUNTERMEASURES

While the findings were not particularly robust, there were some suggestions of suitable countermeasures to reduce the injuries observed in the crashed vehicle study. Many of these measures have already been suggested from a previous study (CR95) for passenger cars.

STEERING ASSEMBLY: The steering wheel and assembly has been shown to inflict injury to drivers of these special purpose cars. This is in spite of the fact that 98% of the occupants whose belt wearing status could be determined were properly restrained. Steering wheel related countermeasures worthy of consideration include supplementary air bags, belt tighteners and webbing clamps, padded steering wheels, or no steering wheel at all.

IMPROVED RESTRAINT SYSTEMS: The need for improvements to existing seat belt systems was noted in CR95 for passenger cars and is again highlighted in the injury and contact source findings for this study since upper limb injuries caused by scat belts were the most common. Possible improvements to existing seat belt systems are better seat belt geometry, belt tighteners and webbing clamps, improved front seat design, better positioning of scat belt stalks, seat belt interlocks, as well as other incidental belt improvements.

THE INSTRUMENT PANEL: The instrument panel assembly was a well documented problem area for front seat occupants of current generation passenger cars and was also a cause of significant lower limb injury in this study. There are several possible countermeasures currently available to minimise or alleviate these injuries, such as the use of knee bolsters, improved padding, reduced protrusions, and the use of less injurious instrument panel materials that are more energy absorbing and less likely to shatter.

THE NEED FOR VEHICLE REGULATIONS

Special purpose vehicles such as 4WDs, vans and utilities are not currently subject to the full set of Australian Design Rules that apply to passenger cars and their derivatives. In particular, the only frontal crash requirement is for these vehicles to comply with ADR 1 0/0 1 which specifies maximum steering column intrusion levels. Moreover, there is no current rollover requirement such as a roof strength test for any passenger vehicle (other than buses) sold in Australia.

Given the increasing use of 4WDs vans and utilities for private use as alternatives to passenger cars, it could be argued that they should also be expected to provide similar levels of occupant protection as passenger cars. Thus, a strong case could be mounted for all these special purpose vehicle types to be similarly regulated.

In particular, they should at least be required to meet the new dynamic frontal crash performance requirement ADR69 as well as side impact regulations, either current or proposed for the future.

Given the preponderance of rollovers among 4WD vehicles, it would seem desirable for these vehicles in particular to have to meet a roof strength requirement as well, although the form of this standard may require further consideration.

FURTHER RESEARCH AND DEVELOPMENT

This study highlighted a number of areas requiring further research. Most notably, these findings would be more robust if more data was available on those seriously injured in crashes involving these vehicles. In addition, the cost-effectiveness of many of these measures needs to be established for these vehicles. It had been hoped to gain some appreciation of the injurious nature of bull-bars in this study but this proved not to be possible. There would be considerable merit in mounting such a study in future.