Older drivers and risk to other road users.

This paper examines the degree to which older drivers impose an "excess" risk of death or injury serious enough to require hospitalization on other road users; that is, the amount of risk older drivers impose on others above and beyond the amount imposed by drivers who are not yet old. A data set linking crash information from police accident reports to hospital discharge data in Wisconsin, 1991, was used to analyze excess risk associated with older drivers in two ways. First, the difference in the rate of serious injuries to other road users per 100 million driver age-group miles was used to estimate the total number of serious injuries resulting from the excess risk imposed on others by older drivers. Second, statistical models were used to infer the association between driver age and crash severity while conditioning on a variety of crash-specific information. Drivers aged 65-74 did not appear to impose excess risk of either deaths or injuries requiring hospitalization in either the aggregate or individual level analyses. Drivers aged 75 and over are associated with increased injuries to others, although the actual number is very small; the individual crash-level analysis suggests that a non-trivial part of the excess risk found in the aggregate analysis is a product of confounding.