Graduated driver licensing and teen traffic fatalities

Abstract

Over the last 8 years, nearly every state has introduced graduated driver licensing (GDL) for teens. These new licensing procedures require teen drivers to advance through distinct stages where they are subject to a variety of restrictions (e.g., adult supervision, daytime driving, passenger limits). In this study, we present evidence on whether these restrictions have been effective in reducing traffic fatalities among teens. These evaluations are based on state-by-year panel data from 1992 to 2002. We assess the reliability of our basic inferences in several ways including an examination of contemporaneous data for older cohorts who were not directly affected by these policies. Our results indicate that GDL regulations reduced traffic fatalities among 15–17-year-olds by at least 5.6%. We also find that the life-saving benefits of these regulations were plausibly related to their restrictiveness. And we find no evidence that these benefits were attenuated by an increase in fatality risks during the full-licensure period available to older teens.

Introduction

In a recent report, the Centers for Disease Control and Prevention (CDC, 1999) characterized improvements in motor vehicle safety as one of the 10 great public-health achievements of the 20th century. Over the last 3 decades, these gains have been particularly striking for young adults, the age group with the highest traffic fatality risk. More specifically, between 1975 and 1992, traffic fatality rates for 16–20-year-olds fell from 39 per 100,000 people to 28, a reduction of more than 25% (NHTSA, 2003, Table 6).

These impressive gains are due to a diverse set of factors that includes state and federal policy initiatives like minimum legal drinking ages, mandatory seat-belt laws and drunk-driving regulations (Dee and Evans, 2001). However, since 1992, the annual traffic fatality rate of young adults has been remarkably stable at approximately 29 deaths per 100,000 people (Grabowski and Morrisey, 2001). Furthermore, despite the improvements of the last 30 years, traffic fatalities are still the leading cause of death among young adults, accounting for 6277 deaths of 16–20-year-olds in 2002 alone (NHTSA, 2003, Table 54).

Over the last 8 years, most states have responded to these public-health concerns by introducing graduated driver licensing (GDL) programs for young drivers. The signature feature of these regulations is that they require new drivers to advance through restrictive beginner and immediate phases before they can achieve full licensure. The fundamental intent of these programs is to encourage new drivers to acquire critical driving skills and experience in low-risk and monitored settings. In 1996, the state of Florida implemented the first GDL program in the United States. However, within just 6 years (i.e., by 2002), 38 states had introduced similar policies (Table 1).

These new state-level licensing regulations have, arguably, become the premier policy initiative designed to improve traffic safety among young adults. However, largely because these policies are so recent, we know surprisingly little about their effects. In this study, we present new panel-based econometric evidence on the effects of GDL programs on teen traffic fatalities.

Our study makes several distinct contributions to the literature. First, we rely on the most recently available nationwide data on traffic fatalities (i.e., through 2002). Second, we validate the critical assumptions of our basic “difference-in-differences” (DD) specification by analyzing contemporaneous state-by-year data on traffic fatalities among older cohorts who were not directly affected by GDL regulations. We also synthesize these results by presenting the results of “difference-in-differences-in-differences” (DDD) specifications based on the pooled data. Third, we assess whether the effect sizes associated with GDL policies varied plausibly with the stringency of the state-specific regulations. And, fourth, we present some qualified evidence on whether the ostensible public-health benefits of these regulations were attenuated (or amplified) by changes in the traffic-safety outcomes of older teens who reached full licensure under the new policy regime.

In brief, our results suggest that GDL policies have been quite successful at reducing fatalities among teens. More specifically, our results indicate that these regulations reduced traffic fatalities among 15–17-year-olds by at least 5.6%. We find that these effects were monotonically larger in states with more stringent policies. We do not find evidence that the cohorts subject to these new regulations had higher risks upon reaching full licensure. In the concluding section, we discuss the policy implications of these results in more detail.