In this report, crashworthiness is defined as the rate of serious and fatal crashes per crash of any severity. The relationship between this rate and the ages of passenger vehicles is used to characterise and compare the crashworthiness of the South Australian registered passenger vehicle fleet and the fleets of other Australian jurisdictions.

Newstead et al. (2008) found that the average crashworthiness of vehicles improves with year of manufacture, implying that drivers of newer cars are less likely to be killed or admitted to hospital after a crash.

Their data suggests that the rate of serious and fatal crashes increased 2.53% per year of vehicle age. For this report, Newstead et al.’s empirical relationship was applied to data on vehicle ages in the registered fleet and the crashed vehicle fleet. The analysis was as follows:

• the composition of the South Australian registered fleet was described;
• the distribution of vehicle ages in the South Australian fleet was calculated;
• a comparison was made between the distribution of the ages of the registered passenger vehicle fleet in various Australian jurisdictions, at which point an estimate was made of the relative crashworthiness of the South Australian registered passenger fleet;
• adjustments were made for driving exposure and crash exposure; and finally
• some observations of the ages of vehicles crashed by younger and older drivers were made.
 

Data came from the registration and licensing database held by the Department for Transport, Energy and Infrastructure, the Australian Bureau of Statistics and the South Australian Traffic Accident Reporting System.

The mean age of the passenger vehicles, utilities and vans in South Australia is 10.9 years and the median age is 8.9 years. The mean age varies between vehicle types. For ‘Cars’ the mean age is 11.2 years, ‘Station wagons’ – 9.7 years, ‘Panel vans’ – 12.7 years and ‘Utilities’ – 10.5 years. The mean age of ‘cars’ plus ‘station wagons’, which broadly fits the ABS definition of ‘Passenger vehicle’ is 10.9 years, and the median age is 9.0 years. The average age of the entire registered fleet, minus trailers and caravans is 11.36 years.

Considering only passenger vehicles, and fitting a standard Weibull distribution to the vehicle age data, produced a mean age of 11.2 years for South Australia compared with 9.9 years for the entire Australian registered passenger vehicle fleet and 9.3 years for registered passenger vehicles in New South Wales.

Based on these mean vehicle ages, tow-away crashes in South Australia have a 3% over-representation of seriously injured or killed drivers compared with the national average (assuming a crashworthiness decline of 2.53% per year of vehicle age). The distribution of the ages of passenger vehicles that crash in South Australia is broadly similar to the registered passenger vehicle fleet, but dissimilar to the distribution of vehicle ages in the registered fleet weighted for driving exposure.

Further modelling showed that if the distribution of vehicle ages of vehicles that crash were in line with the distribution of the Australian registered fleet, there would be around 3.5% fewer serious and fatal crashes in South Australia (a result similar to that obtained using the mean age of the fleet).

To effect a 10% decline in such crashes through fleet renewal would require a radical change to the age distribution including a reduction in the mean age to 7.5 years. Young drivers appear to be doubly disadvantaged in that they have a higher rate of serious and fatal crashes for a given vehicle age, and they tend to crash vehicles that are much older on average than the vehicles crashed by other drivers.

Some consideration was given to the ability of periodic motor vehicle inspections to reduce the age of the fleet, but a review of the literature found little evidence for this. There is some evidence that inspections can initially remove the oldest vehicles in the fleet, but after that better maintenance could prolong the service life of vehicles, thereby increasing the age of the fleet.

However it was noted that the States with such inspections schemes do have younger registered fleets. But this apparent relationship is probably confounded by lower rates of vehicle ownership, fewer cars per household, and in the case of New South Wales, higher public transport use.

While this report examined the crashworthiness of the South Australian registered passenger vehicle fleet, it did not investigate any factors that influence the composition of the fleet. Data not published in this report indicate that, in South Australia, the number of vehicles built in a given year tends to increase for up to a decade after the build year, suggesting significant importation of second-hand vehicles from interstate.

Similar data from New South Wales indicated an immediate decline in the number of vehicles of given build year in subsequent years. When looking to affect the safety characteristics of passenger vehicles on the road, it should be borne in mind that the influence of new-car safety on the fleet’s average safety is not immediate.

Of course, if all vehicles were replaced instantaneously with new vehicles, there would be a significant benefit, but the reality is that this benefit takes many years to realise, and new vehicle safety will mainly benefit a future cohort of drivers that are presently young children. In the shorter term, there may well be merit in understanding the impediments to young drivers driving newer (and safer) vehicles; for example, there may be conditions on vehicle insurance which may inhibit the use of newer cars to members of households that are young drivers.

It may be fruitful to focus on trends in vehicle safety technology and other safety related characteristics of the fleet, particularly with vehicles entering the registered fleet for the first time (either as new cars or as imported second-had cars). It is probable that positively influencing the level of safety in vehicles entering the registered fleet will have road safety benefits many years into the future.

There would be a benefit in gaining a clearer picture of how and why vehicles enter the registered fleet and how and why they leave. Knowledge of this aspect of the turn-over of the registered fleet will allow a better understanding of the likely trends in vehicle ages as well as trends in the penetration of vehicle safety technology.