Estimating the exposure and fatal crash rates of suspended/revoked and unlicensed drivers in California.

There have been a number of studies conducted during the past three decades which show that most suspended/revoked (S/R) drivers violate their license action and continue to drive during their period of disqualification. Traffic safety researchers also suspect that S/R drivers are overinvolved in traffic crashes, but this is difficult to demonstrate because of the lack of good data on their prevalence among all road users. This paper applies the quasi-induced exposure method to fatal crash data obtained from the National Highway Traffic Safety Administration's Fatal Accident Reporting System, to generate exposure and crash rate estimates for S/R drivers in California. The results show exposure rates of 8.8% and 3.3% for suspended/revoked and unlicensed drivers, respectively, and that, compared to validly licensed drivers, the former are overinvolved in fatal crashes by a factor of 3.7:1, and the latter 4.9:1. These findings provide support for efforts to better control S/R and unlicensed drivers. The paper also discusses serious limitations to using quasi-induced exposure to estimate the numbers of such drivers on California roads, and concludes that it is not suited to this task.