Evaluation of California's graduated driver licensing program.

Problem: California's graduated driver licensing (GDL) program was implemented to reduce the high crash risk of teenage drivers. The program enhancements made in 1998 were evaluated in this study using methods that rule out the noticeable downward trend in California teen's fatal/injury crash rates as a possible explanation for any observed crash reductions that could otherwise be mistaken for program effects.

Method: Monthly per capita fatal/injury crash rates for 15-to-17-year-olds and proportional representations of 16-17-year-olds' nighttime and passenger crashes were analyzed using intervention time series analysis.