Examining the Safety Implications of Later Licensure: Crash Rates of Older vs. Younger Novice Drivers Before and After Graduated Driver Licensing

Abstract

Introduction

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.

Methods

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 analyzed 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.

Results

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.

Conclusions

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.