Introduction: How do crash and traffic violation rates for novice 16-17-year-old drivers change over the months before and after licensure under a graduated driver licensing (GDL) program relative to those for older novices who are not subject to GDL?
Method: Plots and Poisson regression comparing overall rates and subtypes of crashes and traffic violations among California novice drivers ages 16 to 35 years over time before and after unsupervised licensure.
Results: Majorities of 16-year-olds (57%) and 17-year-olds (73%) actually hold their learner permits longer than the required 6 months; majorities (67%-81%) of age 18 or older novices hold their learner permits less than 6 months. Crash rates of novice 16- and 17-year-olds-as well as most other age groups-are highest almost immediately after they are licensed to drive unsupervised, after which their rates decline quickly during their first year of licensure and at a slower rate for the second and third years. Novice 16- and 17-year-olds' traffic violation rates reach their zenith long after their total crash rates peak and decline, whereas violation rates for older novices peak during their first year of licensure. Over 70% of 16- and 17-year-old novices are crash-free for the first 3 years of licensure.
Conclusions: While novice 16- and 17-year-olds' highest crash rates occur almost immediately after they are licensed, their peak traffic violation rates are delayed until around the time they turn age 18. Both pre-licensure crash rates and post-licensure crash peaks were more pronounced for some older age groups of novices than was the case for 16-17-year-olds.
Practical applications: Extending learner permit holding periods for 16-17-year-old novices appears consistent with their actual behavior; requiring older novices-particularly those ages 18 to 20-to hold permits for minimum periods may reduce their initial crash rates.
Keywords: Crashes; GDL; Graduated driver licensing; Novice drivers; Traffic violations.
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