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.


OBJECTIVE
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.
Center for Injury Research and Prevention; Center for Clinical Epidemiology and Biostatistics. Electronic address: currya@email.chop.edu.
Allison E
AE
Curry
Department of Biostatistics, School of Public Health; Survey Methodology Program, Institute for Social Research, University of Michigan, Ann Arbor, Michigan.
Michael R
MR
Elliott
Center for Injury Research and Prevention.
Melissa R
MR
Pfeiffer
Center for Injury Research and Prevention.
Konny H
KH
Kim
Center for Injury Research and Prevention; Department of Pediatrics, Division of Emergency Medicine, the Children's Hospital of Philadelphia; Center for Clinical Epidemiology and Biostatistics; Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.
Dennis R
DR
Durbin
D000063:Accidents, Traffic / Q000517:prevention & control* / Q000706:statistics & numerical data*; D000293:Adolescent; D001334:Automobile Driving / Q000331:legislation & jurisprudence*; D006801:Humans; D008004:Licensure / Q000331:legislation & jurisprudence*; D033242:Minors / Q000331:legislation & jurisprudence; D009515:New Jersey; D055815:Young Adult