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Evaluation of California's graduated licensing system

Zwicker, Thomas J.; Williams, Allan F.; Chaudhary, Neil K.; Farmer, Charles M.
Insurance Institute for Highway Safety
August 2006

Objective: Evaluations of several state graduated licensing programs have indicated reductions in injury and fatal crashes involving 16-year-old drivers. However, results of evaluations of California?s July 1, 1998 graduated licensing law have been mixed, with one study showing no overall reduction in crashes. The present study attempted to clarify the effects of California?s law.
Methods: Auto-Regressive Integrated Moving Average time series analysis was used to account for pre-existing downward trends and seasonality in monthly 16-year-old driver involvements in injury or fatal crashes per 10,000 population, based on 1995-2003 data. Monthly 24-55-year-old driver involvements in injury/fatal crashes per 10,000 population were used as an additional check for statewide trends.
Results: Implementation of the graduated licensing law resulted in an estimated 23 percent reduction in 16-year-old driver injury and fatal crash involvements. An estimated 8,052 16-year-old driver involvements in injury and fatal crashes were prevented in the 66 months following the law?s implementation. Sixteen-year-old driver involvements in injury and fatal crashes with injured teenage passengers declined by an estimated 38 percent, or 3,953 fewer crash involvements. Nighttime and daytime 16-year-old driver involvements in injury and fatal crashes were reduced by similar amounts.
Conclusions: California?s graduated licensing law has reduced 16-year-old driver involvements in crashes. The results differ from those of Masten and Hagge (2003) who found no overall effects for 16 year-olds. Their modeling process was overly restrictive and did not adequately account for seasonal and other systematic nonlinear periodic trends in injury and fatal crashes.