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Long-term changes in crash rates after introduction of a graduated driver licensing decal provision

New Jersey (NJ) implemented the first Graduated Driver Licensing (GDL) decal provision in the US 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, according to the authors of a study published in the American Journal of Preventative Medicine.
The study evaluated the longer-term (2-year) effect of NJ’s decal provision on overall and age-specific crash rates of young drivers with intermediate licenses.
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 modelling 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.
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.
The authors conclude that 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.
Source: Long-Term Changes in Crash Rates After Introduction of a Graduated Driver Licensing Decal Provision. Allison E. Curry, PhD, MPH, Michael R. Elliott, PhD, Melissa R. Pfeiffer, MPH, Konny H. Kim, MPH, Dennis R. Durbin, MD, MSCE. American Journal of Preventative Medicine, February 2015, Volume 48, Issue 2, Pages 121–127.

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