Graduated Driver Licensing Systems: Title and subTitle BreakReducing Crashes Among Teenage Drivers

Whether based on miles driven or population, the crash risk for teenage drivers in the United States exceeds that for any other age group. The crash risk is highest among 16- and 17-year-old drivers,¹ presumably due to the increased exposure and risks associated with the initiation of independent driving. The amount of driving increases dramatically when teenagers obtain a driver's license,² and the risk of a crash or citation is considerably higher during the first few months and the first 500 miles driven following licensure than during subsequent months.³

Beginning in the mid-1990s, several states in the United States began to embrace the concept of graduated driver licensing (GDL) for teenage drivers. By phasing in driving privileges and limiting initial driving to situations of lesser risk, GDL has great potential for reducing crashes among teenagers. Three-stage GDL systems allow full licensure only after completion of a learner's stage (supervised driving only) and an intermediate stage (unsupervised driving only in low-risk situations).

Forty-three states and the District of Columbia have enacted 1 or more GDL elements, and 34 states and the District of Columbia have a 3-stage system.⁴ Particularly promising features are limitations on driving at night and transporting teenage passengers. In 1999, 41% of motor vehicle deaths among teenagers occurred between 9 PM and 6 AM¹ ; pre-GDL studies found lower crash rates in states with night driving restrictions.⁵ Currently, 34 states have night driving restrictions for teenage drivers. Transporting passengers increases the crash risk for young drivers; the risk increases with the number of passengers, with teenage passengers, and for drivers ages 16 to 17 years compared with those aged 18 to 19 years.^{6 - 8} Graduated driver licensing systems in 14 states include restrictions on driving with teenage passengers.⁴

In this issue of THE JOURNAL, Shope et al⁹ and Foss et al¹⁰ report evaluations of GDL systems implemented in 1997 in Michigan and North Carolina, respectively. Comparing 1999 with 1996 and adjusting for populationwide trends, crashes involving 16-year-old drivers declined 25% in Michigan and 27% in North Carolina. These results, although preliminary, are particularly encouraging because these states' GDL systems are among the most stringent. The findings follow positive evaluations of GDL systems in Florida,¹¹ New Zealand,¹² Nova Scotia,¹³ and Ontario.¹⁴

Shope et al⁹ and Foss et al¹⁰ note that their results pertain only to the overall effects of the GDL systems. It was impossible at this stage to assess the relative effectiveness of specific GDL elements or to determine the level of compliance with GDL requirements. However, in both states, crash reductions were substantially greater during the hours covered by the night restrictions for newly licensed drivers than during other hours. The evaluation of Florida's GDL system yielded similar results; greater crash reductions occurred during night curfew hours.¹¹ Thus, nighttime restrictions appear to be an effective element of GDL systems.

Although the Michigan and North Carolina laws were not necessarily intended to delay licensure, this outcome was apparently a consequence of enhanced licensing requirements and likely contributed to crash reductions. Delay in licensure was more evident in Michigan, where the number of licensed 16-year-olds declined by more than one third during the study period.⁹ Although Foss et al¹⁰ reported a slight decline from 1996 to 1999 in the percentage of 16-year-olds who were licensed, a potentially large decline may have occurred if "learner's permits" (ie, level 1 licenses) are excluded from the 1999 total.

The results of these 2 studies should be considered within the context of other research on the effects of more stringent licensing requirements. After a 1993 increase in driver education requirements for obtaining a driver's license at 15 years of age, Louisiana experienced a 33% decrease in the number of 15-year-olds who obtained a license and a 20% decrease in the number of 15-year-old drivers involved in crashes.¹⁵ Similarly, after a 1997 increase in licensing requirements that effectively delayed full-privilege licensure for 16-year-olds, Connecticut experienced a 22% decline in crashes for 16-year-olds.¹⁶ Evaluations of GDL systems in New Zealand¹² and Nova Scotia¹³ reported declines in rates of licensure and sizable reductions in crashes. However, Florida's 1996 GDL law was associated with a slight increase in licensure and crash reductions of 9% for drivers 15 to 17 years of age and 11% for 16-year-old drivers.¹¹ Thus, the dramatic crash reductions in Michigan and North Carolina are consistent with reductions in other jurisdictions where delayed licensure was combined with increased learning, more restrictions, or both, during the first few months of independent driving.

Pre-GDL studies indicated that states that delayed licensure (to late age 16 or age 17) fared better than states with early licensure. However, lower crash rates for the youngest drivers (ie, 15- and 16-year-olds) in the delayed-licensure states were partially offset by higher crash rates among older teens once they were licensed. These studies also suggested that if restricted (ie, low-risk) driving was allowed for 16-year-olds, the higher crash rate for full privilege licensing at 17 years could be reduced.¹⁷ Future research in Michigan and North Carolina and elsewhere may help determine any residual (positive or negative) effects of GDL laws when the current age cohort reaches 17 and 18 years.

Given the great life- and injury-saving potential of GDL, further research is needed to evaluate other states' GDL systems and to identify which GDL elements produce the greatest crash effects. To the extent possible, researchers should seek to use measures and methods that facilitate comparisons across jurisdictions, acknowledging the considerable variation in GDL and pre-GDL systems across states. As illustrated by Shope et al⁹ and Foss et al,¹⁰ understanding and documenting teenage drivers' transitions through GDL systems are complex tasks. State crash and driver records may need to be modified to provide sufficient detail on the licensing status of new drivers. Baseline and post-GDL data are needed to assess changes in teenagers' patterns of learning to drive and driving exposure and their compliance with GDL requirements. Hopefully, states currently implementing, or contemplating, GDL systems will gather the data needed to understand which particular GDL elements translate into changed behaviors and reduced crashes. In particular, studies need to determine to what extent crash reductions are attributable to delayed or reduced overall driving exposure (through delayed licensure and driving restrictions), reduced high-risk driving, more practice driving prior to licensure, or safer driving motivated by the desire to advance to the next level of a graduated system.

Such research should provide additional important insights into the mechanisms by which GDL systems reduce motor vehicle crash risk, as well as their potential for reducing crash-related morbidity and mortality. For now, however, the evidence to date suggests that GDL systems are an effective strategy to help meet the formidable challenge of protecting teenage drivers.