Many states require young drivers to get extensive experience, including driving with an adult, before getting a full license. But in most states those laws only apply to those younger than 18. The new study suggests some teens are just putting off getting a license until they turn 18 - meaning they have little experience and higher odds for a deadly crash.
"There's an incentive right now to skip out and just wait until you're 18," said Scott Masten, the study's lead author and a researcher with California's Department of Motor Vehicles. "In most states you don't even need to have driver education or driver training" if you obtain a license at 18, he said.
"I was actually bummed by my own findings - to find out we're offsetting the benefits" in young drivers so much, he said. "It was quite unexpected."
The study examined fatal crashes from 1986 to 2007 involving 16- to 19-year-olds. Results appear in Wednesday's Journal of the American Medical Association.
Most previous studies have also linked graduated licensing programs with a decline in fatal crash rates among young teens, but evidence on effects in older teens is mixed.
A journal editorial by researchers with the Insurance Institute for Highway Safety said the potential effects in older teens "is a serious issue deserving attention by researchers and policymakers." The editorial noted that New Jersey is one of the few states where graduated driver's licensing restrictions apply to all first-time applicants younger than 21. That has led to lower crash rates among 17- and 18-year-olds.
Whether these programs should be extended to include older teens merits further study, the editorial said.
Every state has some type of graduated driver's licensing program. These typically allow full, unrestricted licenses to kids younger than 18 only after several months of learning while driving with an adult, followed by unsupervised driving with limits on things like night driving and the number of passengers.
The study authors analyzed fatal crash data from the National Highway Traffic Safety Administration and information on each state's licensing programs.
Comparing states with the most restrictions versus those with the weakest laws or no restrictions, there were 26 percent fewer fatal crashes involving 16-year-old drivers; but among 18-year-old drivers, there were 12 percent more fatal crashes. The differences are estimates, taking into account factors that would also influence fatal crash rates, including seatbelt laws, changes in minimum speed limits, and the fact that 18-year-old drivers outnumber 16-year-old drivers.
The programs appeared to have no effect on fatal crash rates for drivers aged 17 and 19.
Researchers estimate that since the first graduated licensing program began in 1996, the programs have been associated with 1,348 fewer fatal crashes involving 16-year-old drivers but with 1,086 more fatal crashes involving 18-year-old drivers.
During the 1986-2007 study, there were nearly 132,000 fatal crashes of drivers aged 16 to 19. Nearly 20 percent involved 16-year-old drivers, while almost 30 percent involved 18-year-olds.
Evidence suggests that many teens are waiting until they're older to get their licenses; in California for example, only 13 percent of 16-year-olds have driver's licenses, Masten said.
In a nationwide survey of almost 1,400 teens published last month in the journal Traffic Injury Prevention, 1 in 4 who were 18 and hadn't obtained a license cited the hassle of licensing requirements as a reason.
Masten said more research is needed to determine why the fatal crash rate among 18-year-olds rose and whether an increase also occurred in nonfatal crashes.
The study confirms that graduated licensing "is doing what it was intended to do - prevent novice drivers from being in high-risk conditions before they're ready for it," said Dr. Flaura Winston, a pediatrician and traffic injury expert at the Children's Hospital of Philadelphia. But the results also show there's a need for strategies for the novice independent driver at any age, she said.