Long-term changes in crash rates after introduction of a Graduated Driver Licensing decal provision.

Background: New Jersey (NJ) implemented the first Graduated Driver Licensing (GDL) decal provision in the U.S. in May 2010. An initial study reported a 1-year post-decal decrease in the crash rate among NJ intermediate drivers aged <21 years. Longer-term analysis is critical for policymakers in other states considering whether to implement a decal provision.

Purpose: To evaluate the longer-term (2-year) effect of NJ's decal provision on overall and age-specific crash rates of young drivers with intermediate licenses.

Methods: Monthly per-driver police-reported crash rates during January 2006-June 2012 were estimated. Specific crash types included injury, midnight-4:59am, single-vehicle, multiple-vehicle, and peer passenger crashes. Negative binomial modeling compared pre- versus post-decal crash rates, adjusting for age, gender, calendar month, gas price, and 21- to 24-year-old licensed driver crash rates; piecewise negative binomial regression models accounted for pre-decal crash trends among intermediate drivers. Analyses were conducted in 2013.

Results: The adjusted crash rate for intermediate drivers was 9.5% lower in the 2-year post-decal period than the 4-year pre-decal period (95% CI=0.88, 0.93). Crash rates decreased 1.8% per year before the provision and 7.9% per year in the post-decal period (p<0.001 for difference in slopes). For several crash types, effects appeared to be particularly strong for 18- and 19-year-olds. An estimated 3,197 intermediate drivers had crashes prevented.

Conclusions: NJ's decal provision was associated with a sustained decline in intermediate driver crashes. Future research should aim to better understand the causal mechanism by which NJ's decal provision may have exerted an effect.