Young driver crash rates by licensing age, driving experience, and license phase.
BACKGROUND
Few studies have concurrently assessed the influence of age and experience on young driver crashes, in particular in the post-Graduated Driver Licensing (GDL) era. Further, little attention is given to the transition from intermediate to full licensure. We examined the independent and joint contributions of licensing age, driving experience, and GDL license phase on crash rates among the population of young New Jersey (NJ) drivers.


METHODS
From a unique linked database containing licensing and crash data, we selected all drivers who obtained their NJ intermediate license at 17-20 years old from 2006-2009 (n=410,230). We determined the exact age at which each driver obtained an intermediate and full license and created distinct, fixed cohorts of drivers based on their age at intermediate licensure. For each cohort, we calculated and graphed observed monthly crash rates over the first 24 months of licensure. Further, we examined crash rates by age at licensure, driving experience (i.e., time since licensure), and license phase.


RESULTS
First-month crash rates were higher among the youngest drivers (licensed at 17y0m). Drivers who were licensed later experienced a reduced "steepness" in the slope of their crash rates in the critical initial months of driving, but there did not appear to be any incremental benefit of later licensure once drivers had six months of driving experience. Further, at each age, those with more driving experience had lower crash rates; however, the benefit of increased experience was greatest for the substantial proportion of teens licensed immediately after becoming eligible (at 17y0m). Finally, independent of age and experience, teen drivers' crash risk increased substantially at the point of transition to a full license, while drivers of a similar age who remained in the intermediate phase continued to experience a decline in crash rates.


CONCLUSIONS
Age and driving experience interact to influence crash rates. Further, independent of these two factors, there is an abrupt increase in crash risk at the point of transition from intermediate to full licensure. Future studies should investigate whether this increase is accounted for by a change in driving exposure, driving behaviors, and/or other factors.
Center for Injury Research and Prevention, The Children's Hospital of Philadelphia, 3535 Market Street, Suite 1150, Philadelphia, PA 19104, USA; Center for Clinical Epidemiology and Biostatistics, Perelman School of Medicine at the University of Pennsylvania, 423 Guardian Drive, Philadelphia, PA 19104, USA. Electronic address: currya@email.chop.edu.
Allison E
AE
Curry
Center for Injury Research and Prevention, The Children's Hospital of Philadelphia, 3535 Market Street, Suite 1150, Philadelphia, PA 19104, USA. Electronic address: m.rileypfeiffer@gmail.com.
Melissa R
MR
Pfeiffer
Center for Injury Research and Prevention, The Children's Hospital of Philadelphia, 3535 Market Street, Suite 1150, Philadelphia, PA 19104, USA; Center for Clinical Epidemiology and Biostatistics, Perelman School of Medicine at the University of Pennsylvania, 423 Guardian Drive, Philadelphia, PA 19104, USA; The Department of Pediatrics, Division of Emergency Medicine, The Children's Hospital of Philadelphia, Perelman School of Medicine, University of Pennsylvania, 3401 Civic Center Blvd., Philadelphia, PA 19104, USA. Electronic address: durbind@email.chop.edu.
Dennis R
DR
Durbin
Department of Biostatistics, School of Public Health, University of Michigan, 1415 Washington Heights, Ann Arbor, MI 48109, USA; Survey Methodology Program, Institute for Social Research, University of Michigan, Rm. 4068, 426 Thompson Street, Ann Arbor, MI 48109, USA. Electronic address: mrelliot@umich.edu.
Michael R
MR
Elliott
D000063:Accidents, Traffic / Q000706:statistics & numerical data*; D000293:Adolescent; D000367:Age Factors; D001334:Automobile Driving / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D008004:Licensure / Q000706:statistics & numerical data*; D008297:Male; D009515:New Jersey; D055815:Young Adult
Adolescent drivers; Graduated Driver Licensing; Motor vehicle crash risk; Novice teen driver; Probationary period; Provisional license