Older driver crash rates in relation to type and quantity of travel.

It is a well-established phenomenon that, notwithstanding their overall good crash record, older drivers have a higher than average rate of involvement in injury crashes when the rate is calculated by dividing crash numbers by distance driven. It has been hypothesised that at least some of this higher crash rate is an artefact of the different nature of driving undertaken by many older drivers. For example, driving in congested urban environments provides more opportunities for collisions than driving the same distance on a motorway. However, there have been few opportunities to investigate this theory, as relevant data are difficult to acquire. High-quality data from the New Zealand Travel Survey (1997/1998) were combined with crash data to enable a statistical model to estimate the risk of driver groups under various driving conditions characterised by the type of road used, time of day, day of week, and season of year. Despite elevated crash risks per distance driven compared with middle-aged drivers for most road types, older drivers were as safe as any other age group when driving on motorways. Accounting for the fragility of older drivers and their passengers in the risk estimates for other road types, older drivers appeared to have daytime risks comparable to 25-year-olds and night-time risks as low as any other age group. The driving patterns of older drivers (in terms of when and where they drive) were estimated to minimize their risks in comparison with the driving patterns of other age groups. These results are of interest to both policy makers and transportation planners working against the background of inevitable increases in the number of older drivers as the population ages.