Restrictions on driving by young, new drivers, known as graduated driver licensing programs, substantially decreased the incidence of fatal crashes among the 16-year-old drivers for whom they were designed, according to a report in the Sept. 14 issue of JAMA.
Paradoxically, however, the same programs appear to raise the incidence of fatal crashes for drivers aged 18 and 19, who are not directly subject to the restrictions, said Scott V. Masten, Ph.D., of the California Department of Motor Vehicles’ research and development branch, Sacramento, and his associates.
All 50 states and the District of Columbia have adopted graduated driver licensing (GDL) systems which mandate that novice drivers gain more experience in low-risk conditions before they "graduate," step by step, into driving under riskier conditions. Drivers younger than 18 years can only attain full, unrestricted licensure after they complete a lengthy learning period supervised by an adult. The strongest programs also add steps that limit driving at night and/or driving with multiple underage passengers.
Dr. Masten and his colleagues assessed data from the nationwide Fatality Analysis Reporting System for the period from 1986 through 2007, which included information on all drivers, crash circumstances, and vehicles (including passenger cars, light pickup trucks, vans, and sports-utility vehicles) that involved a death.
In unadjusted analyses, the rates of fatal crashes for each age separately – 16-year-olds, 17-year-olds, 18-year-olds, and 19-year-olds – as well as the rate of fatal crashes for all teenagers combined were consistently lower in states that had three-step GDL programs than in states that did not. The unadjusted rate of fatal crashes for all adolescents combined was 29.7 per 100,000 person-years with the strongest GDL programs, 36.8 per 100,000 person-years with weaker GDL programs, and 47.2 per 100,000 person-years in programs with none of the key GDL elements.
However, in adjusted analyses, GDL programs were associated with a lower incidence of fatal crashes only among 16-year-old drivers. In addition, stronger programs appeared to decrease the rate more effectively than weaker programs among 16-year-olds. But both types of programs slightly raised the rate among 18- and 19-year-olds.
"Since enactment of the first program in 1996, GDL programs (weaker and stronger combined) are estimated to have been associated with 1,348 fewer fatal crashes involving 16-year-old drivers but with 1,086 more involving 18-year-old drivers," the investigators said (JAMA 2011;306:1098-1103).
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Attempts to ease young drivers into high-risk situations through graduated driver licensing programs have returned mixed results.
The reasons for the paradoxical increase among older teens are not known. "Mandatory periods of supervised driving clearly reduce risk while novices learn how to handle a vehicle, gain insights into the behaviors of other drivers, and develop understanding of the physical driving environment.
"Supervised driving, however, is co-driving, and some important lessons of experience, such as the need for self-regulation and what it means to be fully responsible for a vehicle, cannot be learned until teens begin driving alone. Under GDL, this now occurs at least 6 months later, reducing the [total] time that young drivers have to learn from driving on their own before they are 18," Dr. Masten and his associates noted.
"Research is needed to determine what accounts for the increase among 18-year-old drivers and whether this increase occurs among nonfatal crashes as well," they added.
Unfortunately, there is no state-specific national database of nonfatal crashes in the United States.
The investigators cautioned that fatal crashes "represent a small and atypical subset of all crashes." They are much more likely than nonfatal crashes to involve high-risk behaviors such as drinking and speeding. GDL programs’ major influence would be on crashes attributable to lack of understanding rather than to crashes attributable to risky behavior, they said.
No conflicts of interest were reported.