ARE RECENT AUSTRALIAN CARS SAFER OR ARE THEY JUST BIGGER? Diana L. Rosman, & G. Anthony Ryan Road Accident Prevention Research Unit The U niversity of Western Australia Western Australia ABSTRACT The Australian Design Rules (ADRs) have set standards for occupant protection in private and commercial vehicles since 1968. In order to measure the impact of these design changes, the crashworthiness of vehicles manufactured from 1970 to 1995 was estimated from records of crashes occurring in Western Australia between 1987 and 1996. These crash records included crash site and driver information as weil as the year of manufacture and the make, model and mass of each· vehicle involved. The risk of serious injury (hospital admission or death) in tow away crashes was estimated using multiple logistic regression. Adjustments were made for driver age, to hospital or death was gender, speed zone, vehicle mass and mass ratio. Admission derived from police crash reports that were linked to hospital discharge or death records in the W A Road Injury Database. The median mass of crashed vehicles decreased from 1300 kg in 1970 vehicles to 1100 kg in 1985 vehicles and increased again to 1300 kg in 1995 vehicles. There were reductions in the proportion of drivers with serious injury over vehicle manufacture years 1970 to 1980. The estimated risk of serious injury to drivers of 1980s passenger cars was approximately two-thirds the risk for l 970s vehicles in most crash situations. However, there was virtually no improvement in crashworthiness of vehicles manufactured after 1990, when corrected for vehicle mass. SUBST ANTIAL CHANGES HAVE OCCURRED in the design of passenger vehicles over the past 30 years. In Australia this has been driven in part by the reguJatory requirements of the Australian Design Rules (ADRs) introduced in 1968. Crash testing of new cars has been carried out in Australia since 1993 by the New Car Assessment Program to demonstrate the occupant protection capabilities of vehicles tested. IRCOBJ Conference - Göteborg, September 1998 43 BACKGROUND In Australia, Newstead & Cameron ( 1997) demonstrated that crash outcomes for drivers of particular makes and models of vehicles were consistent with test results from the New Car Assessment Program (NCAP). Specifically, reductions in the risk of head and ehest injury in real crashes were of the same order as head and ehest injury criterion scores obtained from NCAP results. In addition, despite significant differences between certain makes and models of vehicles, it was confirmed that on average a driver in a l 990s vehicle had a significantly lower risk of injury than that experienced by a similar driver in a l 970s vehicle. The Monash University Accident Research Centre has also measured the 'crashworthiness' and 'aggressivity' ratings for particular makes and rnodelsof passenger cars (Cameron et al, 1997). A British index, developed by Broughton ( 1996), demonstrated a linear relationship with mass. The index was derived from two-car crashes where at least one driver was injured and was defined to be 'the proportion of vehicles with an injured driver compared to all such drivers'. Using information on two vehicle crashes from the US Fatal Accident Reporting System (FARS), Evans & Frick (1994) found a relative safety disadvantage of small compared to large cars that was less for post- 1980 cars than for pre-1980 cars. This reduced mass effect for mid-l 980s cars was attributed to improved safety features appearing in small cars earlier than in !arge cars. In the present study we have examined the effect of mass and relative mass in single and multiple vehicle collisions after correcting for driver age, gender, crash type and speed zone. The information was derived from police crash reports linked to hospital and death records. METHODS In Western Australia road crashes resulting in injury or property damage exceeding $1000 should be reported to the police. The Traffic Accident System (T AS) contains details from these reports as well as vehicle licence details and additional road si information. Records of all crashes occurring between 1 st J anuary 1987 and 31 December 1996 have been extracted and linked to hospital admission and death registration records .to form the W A Raad Injury Database (Ferrante AM, et al, 1993). Records of all drivers of standard passenger vehicles involved in road crashes requiring a vehicle to be towed from the scene were selected for this study. In the TAS, for collisions between two vehicles, one is defined as the 'colliding' vehicle and the other as the 'target' vehicle. The 'target' is usually the vehicle least likely to be 'at fault' ie, the vehicle in front in a rear impact; the vehicle hit on the side in a right angle collision; and the vehicle travelling on the correct side of the road in a front impact. For this analysis a driver was clefined as being 'seriously' injured if there was a matching hospital admission or death record. The speed zone at the crash location was a proxy for vehicle travelling speed and the vehicle mass was its 'tare weight'. The risk of serious injury was estimated by using multiple logistic regression models in which adjustments were made for time of day, speed zone, driver age and gender, vehicle mass and mass ratio. Driver injury only was used as the measure of crashworthiness since the presence of uninjurecl passengers was not recorded in the crash data. 44 IRCOJJI Co11fere11ce - Giiteborg, September 1998 RESULTS In W A, during the l 0-year period 1987- 1 996, 52,890 passenger vehicles were involved in single vehicle crashes reported to the police and 35,201 of these vehicles were towed from the scene. Over the same period, 496,396 passenger vehicles were involved in reported multi-vehicle crashes resulting in 113,447 vehicles being towed away. Complete vehicle and driver information was available for 28,344 vehicles in multi-vehicle tow-away crashes and for 13,218 single vehicle crashes. PROPORTION OF DRIVERS INJURED 1872 (14.2%) drivers were seriously injured in single vehicle tow-away crashes, while 506 (3.6%) were seriously injured in multi-vehicle tow-away crashes. Figure 1 shows the proportion of drivers who were seriously injured for each vehicle model year. In single vehicle crashes the proportion of drivers with serious injury (l7 .3%) was highest in vehicles manufactured between 1970 and 1974, feil to a minimurn of 12.6% in vehicles rnanufactured in the 1980-1984 period and rose to 14.4% in post- ! 995 vehicles. In rnulti-vehicle crashes, the proportion of drivers with serious injury in the 'target' vehicle fe il from 5.4% in 1970- 1974 models to 2.7% in vehicles manufactured after 1995. Similarly, the proportion of seriously injured drivers in the 'colliding' vehicle feil from 4.5% in 1970- 1974 models to 2.1 % in vehicles rnanufactured after 1995. The greatest reduction in all three groups occurred for vehicle model years 1970 to 1984. 20 18 -.t.- colliding -....target single -•- 16 14 • 12 . 'tl ·� � 10 . .=. E 8 '#. 6 • • 4 • 2 • 1970-1974 1975·1979 1980-1984 1985·1989 1990-1994 1995+ year of manufacture Figure 1 Serious injuries to drivers in tow-away crashes, Western Australia 1987- 1996. LOGISTIC REGRESSION MODELLING In the second part of the analysis, the risk of serious injury was estimated using logistic regression models. A simple model, using only year of vehicle manufacture to predict risk of injury was developed first. The effect of year of vehicle manufacture was initially measured as a 'dass' variable with a separate coefficient for each year. Other models using linear, quadratic and cubic trends for the year of manufacture were fitted to the data. The quadratic trend fitted the crash data best for all situations and is displayed with the point estimates in Figures 2, 3 and 4 for single, colliding and target vehicles respectively. IRCOBI Cmiference - Göteborg. September 1998 45 0.3 --singlo yoars • · quadralic 0.25 � .2. 0.2 . .Cl) E :l 0.15 . .g Q) Cl) ""' 0.1 ·� 0.05 1971 1975 1979 1983 1987 1991 1995 year of manufacture Figure Estimated risk ol' serious to clrivers 2. injury in si ngle vehicle tow away crashes, Western Australia 1987- 1996 0.1 -single years · · · quadratic 0.00 . >- „ ::l :s-1/) 0.06 . ::l 0 · 1/) � 0.04 0 ""'1/) ·;::: 0.02 . 0 1971 1975 1979 1983 1987 . 1991 1995 year of manufacture Figure 3 Estimated risk of serious injury to drivers of colliding vehicles in multi-vehicle tow away crashes, Western Australia 1987-1996. 46 IRCOBI Conference - Giitebor,::. September 1998 0.1 -single years - - - quadratic 0 08 >- :; :� (/) 0.06 ::J ·0� (/) 0 ""' ·(/);: 0.02 0 1971 1975 1979 1983 1987 1991 1995 year of manufacture Figure Estimated risk of serious inj ury to drivers of target vehicles 4 in multi-vehicle tow away crashes. Western Australia 1987- 1996. The estimated risk of serious injury to drivers of 1980s passenger vehicles was approximately two-thirds that for drivers in similar l 970s vehicles in most crash situations. The models suggest an increase in risk for vehicles manufactured after 1985 involved in single vehicle crashes or as 'targets' in multi-vehicle crashes. The actual data for single vehicle crashes indicates an increase in risk between 1985 and 1990. DRIVER AGE lt is known that age is associated with increased risk of injury (eg, Ryan et al, 1998) and there is also a tendency for young drivers to drive older vehicles. In the 1987-1996 crash data, there was a significant relationship between driver age and vehicle year of manufacture for all crash types. Figure 5 shows the median driver age by vehicle model year for single, colliding and target vehicles.