McCartt, Anne T.; Mayhew, Daniel R.; Braitman, Keli A.; Ferguson, Susan A.; Simpson, Herbert M.
Traffic Injury Prevention (TIP)
Although both youth and inexperience contribute to the elevated crash rates of teenage drivers, the relative contribution of these factors has not been firmly established.Methods:
A review was undertaken of eleven recent (1990 or newer) studies that tried to separate the crash effects of age and experience, represented by length of licensure.Results:
The weight of evidence is that age and experience have important, independent effects on crash risk, even after differences in driving mileage are accounted for. The studies consistently found that teenage drivers had dramatically higher crash rates than older drivers, particularly drivers older than 25, after controlling for length of licensure. Studies that distinguished 16-year-olds found that crash rates for novice 16-year-olds were higher than rates for novice 17-year-olds, but crash rates for novice 17-year-olds were not consistently higher than rates for novice 18- to 19-year-olds. With regard to experience, the weight of evidence suggests a steep learning curve among drivers of all ages, particularly teenagers, and strong benefits from longer licensure. Of the studies that attempted to quantify the relative importance of age and experience factors, most found a more powerful effect from length of licensure.Conclusions:
The findings lend support to delaying licensure among teenagers in the United States, where licensure commonly is allowed at age 16, and to graduated licensing systems that phase in unsupervised driving during high-risk situations as teenagers gain independent driving experience.