Research looks at impact of tougher U.S. teenage driving laws

By Dr. Ananya Mandal, MDSep 15 2011

According to a nationwide survey tougher licensing laws for teenage drivers have reduced deadly accidents among 16-year-olds, but have led to increasing the fatal crash rate among 18-year-olds.

Over the last two decades, many states have put in place strict teenage driving laws, with graduated driver license programs that require young drivers to meet certain restrictions before they obtain a full license. While the rules vary by state, they generally set a minimum age for earning a driver’s permit or license and require a set number of supervised hours behind the wheel, and some prohibit driving with fellow teenagers, ban night driving or require at least six months of instruction before a driver’s test.

These tough regulations have been credited with a 30 percent drop in teenage highway fatalities. But these encouraging studies have looked at 16-year-olds only said Scott Masten, a researcher with California’s Department of Motor Vehicles in Sacramento and the lead author of the current study. “When you do that you go, ‘Wow, these programs are saving lives,’” he said.

Dr. Masten and his colleagues looked at data on fatal crashes involving 16- to 19-year-olds that occurred over a 21-year period, beginning in 1986. “When you look at the bigger picture across 18- and 19-year-olds, it looks like we’re offsetting those saved crashes,” he said. “In fact, 75 percent of the fatal crashes we thought we were saving actually just occurred two years later. It’s shocking.”

The study, published Wednesday in The Journal of the American Medical Association, found that since the first graduated driver programs were instituted, there have been 1,348 fewer deadly crashes involving 16-year-old drivers. But at the same time, there have been 1,086 more fatal crashes that involved 18-year-olds. The net difference is still an improvement, Dr. Masten said, but not quite the impact that many had assumed. “The bottom line is there is still a net overall savings from introducing all these programs,” he said. “So we are saving teen drivers overall, but it’s not nearly what we thought it would be.”

The authors speculate that the reason for the increase in deadly crashes among 18-year-olds is that many teenagers, rather than deal with the extra restrictions for 16- and 17-year-olds, are simply waiting to get a license until they turn 18, and skipping the restrictions altogether. As a result, a greater proportion of inexperienced drivers hit the road at 18. To support this theory Masten notes that when California instituted its tougher driving laws for teenagers, the proportion of 16- and 17-year-olds getting licenses to drive dropped while the numbers at 18 and 19 did not.

Authors also suggest that teenagers going through graduated driver license programs are not getting as much practical driving experience when they have “co-drivers.” In other words, while having adult supervision in the car reduces risk, it also protects teenage drivers so much that they miss out on learning experiences that can only be gleaned by driving alone, like knowing what it means to be fully responsible for a vehicle and knowing how to “self-regulate.”

“Even though we want you to learn by driving with your parents, it’s really different from the sorts of things you learn when you’re driving on your own,” Dr. Masten said. “The whole thing about learning to drive is you need to expose yourself to crash risk to get experience.”

In an editorial that accompanied the study, researchers with the Insurance Institute for Highway Safety, a nonprofit group financed by insurance companies, said the findings raised a “serious issue” that policy makers should take note of. They pointed out that one of the state’s with the toughest programs for teenage drivers is New Jersey, where all first-time drivers under 21 have to adhere to graduated driver restrictions. “New Jersey’s approach has been associated with significant reductions in the crash rates for 17- and 18-year-olds and virtually eliminates crashes among 16-year-olds, without adversely affecting crash rates for 19-year-old drivers,” the authors wrote.

However Masten said that same rules apply to New Jersey. In New Jersey, a study of deadly crashes did not look specifically at 21-year-olds; they were mixed into a larger group of 20- to 24-year-olds. But the research still found a 10 percent increase in deadly crashes in that group after New Jersey’s tougher graduated driver licensing program was instituted, suggesting that 18, 19- and 20-year-olds may be waiting out the tough restrictions there as well.

Lack of sleep can also be a major factor in teenage crashes. One study in The Journal of Clinical Sleep Medicine this year found that teenagers who started school earlier in the morning had higher crash rates.

Jackie Gillan, of Advocates for Highway and Auto Safety, says there are three key components to an effective graduated license program: restricting the number of passengers, restricting night time driving and preventing cell phone use. “It's not just the teen drivers who are dying on our highways,” Gillan said. “It's the teen passengers and it's other people like you and me who are sharing the road with these teens.” She added, “When states (enact an effective graduated license program), we have found that it almost immediately results in saving lives.”

Safety advocates are now pushing Congress to pass a federal graduated licensing law. Gillan said, “It doesn't make sense, when we know that they will save so many lives, to have a different set of rules for different rules in different states.”

“The expectation was that older [teen] drivers wouldn't be affected much one way or the other, so this is a new thing to think about,” says Anne McCartt, senior vice president for research at the Insurance Institute for Highway Safety, an Arlington, Va.-based nonprofit organization dedicated to reducing traffic deaths and accidents. But McCartt, who co-authored an editorial accompanying the new study, says this and other research suggests that licensing programs do help protect younger teen drivers. Although “the evidence is mixed at this point about how GDL affects older teens,” she says, “I don't think there's any study that hasn't found a large benefit for 16-year-olds.”

The study had some important limitations that will need to be addressed in future research. For one, the authors looked only at fatal accidents, which account for a small percentage of all crashes and aren't representative of accidents as a whole. (Alcohol and speeding are more often a factor in fatal crashes, for example.)