Examining the safety implications of later licensure : crash rates of older versus younger novice drivers before and after graduated driver licensing.

Crash involvement by 16- and 17-year-old drivers has decreased substantially over the past 15 years. This is largely due to the widespread adoption of Graduated Driver Licensing (GDL) programs and to the Great Recession, which substantially reduced driving by young teenagers. However, with one exception–New Jersey–GDL systems apply only to new drivers younger than 18, and crash reductions have been smaller among older teenage drivers. A recent study estimated that one third of new young drivers do not obtain a license to drive unsupervised until age 18 or later. Historically, studies of novice drivers in the United States have focused on drivers ages 17 and younger; many have only studied 16-year-olds. Individuals who do not begin driving until age 18 or older have rarely been studied in the U.S. The purpose of this study was to examine the crash involvement of newly licensed young drivers up through age 20 in two states–California and North Carolina–for their first three years of unsupervised driving, to determine how crash rates of these novices are related to the age at which they began driving. This was done before and after each state’s GDL system was introduced. Crash involvement during the first three years of licensed driving among drivers who were first licensed to drive unsupervised between May 1, 1997 and December 31, 2004 in California and between January 1, 1996 and December 31, 2004 in North Carolina were examined. Crashes occurring after December 31, 2007 were not included, to avoid possible bias associated with the deep economic recession that ensued. The main outcome measures were the proportion of drivers who remained crash free for varying time periods (e.g., 6 months, 12 months, etc.) after they were licensed. These measures were analysed in relation to the age at which drivers were first licensed. Separate analyses were conducted for all crashes and for crashes that resulted in a reported injury. Before the implementation of GDL, the youngest drivers (licensed at age 16) consistently were the most likely to be involved in crashes both immediately after licensing and cumulatively over their first three years of driving. Licensing at older ages generally was associated with progressively lower crash incidence rates. In both states, new drivers licensed at age 16 under GDL were less likely to be involved in a crash than 16-year-olds licensed before GDL; pre- vs. post-GDL differences in crash rates of those licensed at ages 17 and older were negligible. New drivers licensed at ages 16, 17, and 18 after the implementation of GDL had similar crash incidence rates during their first year of unsupervised driving, but those licensed at ages 19 and older were less likely to be involved in a crash. A notable exception to this pattern was involvement in injury crashes: drivers licensed at age 18 were more likely than drivers licensed at any other age (younger or older) to be involved in a crash resulting in an injury during their first year of licensed driving. The reasons for this are unclear. Initial crash rates and their trajectory during the first three years of licensed driving generally are inversely proportional to age at licensing. Following introduction of GDL, however, individuals licensed at ages 16, 17, and 18 had similar incidence of crash involvement for their first several months of driving. Individuals licensed at age 18 improved more quickly, however, and were involved in fewer crashes in their second and third years of driving. The observed relationship between age at licensure and subsequent crash involvement is not necessarily the result of increasing age or maturity; other studies have shown that individuals licensed at younger versus older ages differ in many ways besides age. Finally, given the minimal effects of GDL observed for individuals licensed at age 17 in both states, as well as the findings from several other studies showing a lesser effect of GDL on 17-year-olds, it is not clear what effect could be expected from extending the GDL provisions presently in effect for 16- and 17-year-olds to older novice drivers. The high first-year incidence of injury crashes among individuals licensed at age 18 suggests a potentially important phenomenon that warrants further research. (Author/publisher)