|Secondary safety refers to mitigation of injury given that a crash occurs, as distinct from prevention of crashes. Evidence is presented that secondary safety of new cars has been improving substantially in recent years.
(a) Single-car crashes, South Australia. The later the year of the car, the smaller is the probability of the driver being killed.
(b) Car-car collisions, South Australia. Comparison of the severities of injury to the two drivers in the one collision is useful because speed of the impact is the same for the two drivers. The basic question is, which driver is killed? It is shown that it is much more likely to be the driver of the older car.
(c) Car-car collisions, New South Wales. The finding was replicated with NSW data. In this case, the sample size was sufficient to include the mass ratio of the cars as a covariate.
In each analysis, allowance was made for some covariates.
Our interpretation of these results is that recent cars genuinely have appreciably better secondary safety than older ones. Possible reasons are discussed.
Our results are from a time period starting several years ago and cars are about a decade old on average. Thus we cannot be sure an improvement is continuing in new cars now: the data is not yet available. The results are nevertheless relevant to the current and future road safety situation. As older cars are scrapped, the proportion of crashes that result in car occupant death will continue to fall for at least one decade into the future.