This study examines whether evidence supports extending Graduated Driver Licensing systems, which most U.S. states apply only to new drivers licensed before the age of 18, to new drivers licensed at ages 18 years or older.
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Graduated Driver Licensing systems have been shown to reduce rates of crashes, injuries, and deaths of young novice drivers. Although new drivers of all ages have elevated crash rates, and an estimated one in three drivers receive their first license at or after the age of 18, most U.S. states only apply Graduated Driver Licensing to new drivers younger than 18. This study investigates whether there is evidence to support extending key components of state Graduated Driver Licensing systems to new drivers ages 18 years and older.
Graduated Driver Licensing (GDL) systems—which place restrictions on new drivers when they first begin driving and then gradually phase in more driving privileges as these drivers gain experience—have been proven to decrease the rates of crashes, injuries, and deaths of young novice drivers. However, although an estimated 1 in 3 new drivers obtain their first license at or after age 18, most U.S. states only apply their GDL systems to drivers younger than 18. (New Jersey applies its full GDL system to all new drivers younger than 21.) Previous studies by the AAA Foundation for Traffic Safety found that new drivers licensed for the first time between the ages of 18 and 20 have crash involvement rates similar to equally-inexperienced new drivers younger than 18 and substantially higher crash rates than same-aged peers who were licensed at younger ages.
Most of the foundational research on GDL systems in the U.S. is based on the elevated crash risk for 16-year-old novice drivers and associated factors. This study sought to determine whether those same factors (e.g., driving at night; carrying multiple passengers) are associated with elevated risk for older novice drivers as well, and thus whether extending existing state GDL systems to slightly older novice drivers would likely have safety benefits.
Researchers from the Children’s Hospital of Philadelphia examined crash involvement rates of newly-licensed drivers in relation to their age and the length of time for which they had been licensed to drive independently.
Drivers were grouped according to whether they received their first license at age 17 years (the minimum age for a license that allows independent driving in New Jersey), 18–20, 21–24, or 25+. Rates of crashes per 10,000 licensed drivers per month were examined for each group for each driver’s first 24 months of licensed driving for all police-reported crashes as well as for:
Rate ratios and 95% confidence intervals, computed using Poisson regression and adjusted for sex, were used to compare crash rates for each of the above crash types for same-aged drivers who had been licensed for different lengths of time, and for different-aged drivers who had been licensed for the same length of time.
Analyses were based on data from 1,034,835 drivers who received their New Jersey driver’s license in years 2006 to 2014, including 327,997 who were aged 18 years or older when they received their first license.
Limitations of the study included inability to account for drivers who moved out of the state of New Jersey during the study period but kept their New Jersey license, and lack of data on the amount of driving done by drivers licensed at different ages overall, over time, and in relation to the specific exposures examined (i.e., driving at night and carrying passengers).