Studying the effects of Graduated Driver Licensing

Since GDL was enacted in North Carolina CSYD researchers have conducted numerous analyses to track its effects and identify needed enhancements.

Early Effects

The original study of early GDL effects was published in the Journal of the American Medical Association, along with a companion study in Michigan. The dramatic crash reductions reported have helped propel other states to emulate the actions and successes of these two early GDL systems. Currently only four states do not have graduated driver licensing systems.

Reactions to GDL

A large majority of adults and teens believe that graduated driver licensing is a good idea. More than 95 percent of North Carolina parents — regardless of whether they lived in an urban or rural area — either “highly approved” or “somewhat approved” of GDL, according a survey conducted by CSYD researchers. Similarly, 80 percent of North Carolina teens, regardless of where they live, were found to either highly approve or somewhat approve of the system.

CSYD researchers have also examined the extent to which critical restrictions in North Carolina's graduated driver licensing (GDL) system are known, adhered to, and enforced. Telephone interviews with 900 teens and their parents, revealed that awareness of North Carolina's night and passenger restrictions was very high among both groups.

Highlights of the findings include:

Interviewers asked about teens’ and parents’ perception of the enforcement of GDL restrictions. Teens expressed little concern about detection, although a majority reported driving more carefully to avoid police notice. Neither parents nor teens knew much about police enforcement of GDL restrictions.

Findings of theses studies are reported more fully in:

GDL and Health Care Costs

A recently completed study, supported in part by a gift from the North Carolina Public Affairs office of State Farm Insurance, documented the cost-reducing effects of GDL by examining hospital discharge data.

Long Term Effects of GDL

Several studies are currently under way to document the nature and magnitude of the long-term effects of graduated licensing on young driver crashes. One of these looks at monthly crash rates for 16 and 17 year-old drivers from 1991 through 2011, to determining whether the initial effects of GDL have continued (they have) and to see how addition of the passenger restriction to the NC GDL program in December 2002 affected crash rates. Another current study is examining the progression of novice drivers through the multiple stages of the licensing system. This is expected to shed light on how well the system is functioning and whether any changes may be needed to improve either its efficiency or effectiveness.

A study completed in 2010 examined whether GDL actually makes for better, i.e., less crash-prone drivers. Numerous studies have now shown that young teen crashes are reduced by graduated licensing, but most, if not all, of the reduction appears to result from reduced driving and less driving in risky conditions, which is one of the primary goals of GDL. An additional expected benefit of GDL, better prepared teen drivers, has yet to be documented. Results of our current study appear to provide the first clear indication that, at least in North Carolina, teens who have been licensed under the GDL system are less likely to crash for several years after they have “graduated” from the protective restrictions of the system. A follow-up to this study is underway to look at how crashes of older (18, 19 & 20) young driver crash rates changed subsequent to introduction of GDL in both North Carolina and California.

Read the full article: Masten, SV & Foss, RD (2010). Long-term effect of the North Carolina graduated driver licensing system on licensed driver crash incidence: A 5-year survival analysis. Accident Analysis & Prevention, 42:1647–1652.

National Studies of GDL

Most of our work on GDL has focused on the North Carolina program. Recently we began to look more comprehensively at the GDL process in an effort to better understand how GDL is working throughout the U.S. One study looked at the association of GDL with fatal crashes among all teenage drivers (i.e., 16 through 19). This produced a somewhat unsettling finding, suggesting that safety gains among younger teens may be offset by losses among older teens. It is not yet clear if this is the case or whether it holds for less severe crashes. Several studies are currently under way to examine these issues as well as possible mechanisms by which an effect might be produced.

Another recently completed national study examined how strongly each of the several individual elements of GDL systems is associated with fatal crashes. Among the several, complex findings, we found that a lengthy learner period (9 to 12 months) and a night driving limit for intermediate licensees that begins at 10 p.m. or earlier were most strongly and consistently associated with a decrease in fatal crash involvement by drivers younger than 18.

Masten, SV, Foss, RD, Marshall SW. (2013). Graduated Driver Licensing Program Component Calibrations and Their Association with Fatal Crash Involvement. Accident Analysis & Prevention, (In press).