U.S. teenagers are crashing less often, both per capita and per mile driven, since the advent of graduated driver licensing (GDL) in the mid-1990s, a new IIHS study confirms. A separate study published recently in Injury Prevention makes the connection with GDL more explicit, finding that graduated licensing reduces both the amount of driving done by teenagers and the likelihood that they will crash when they do drive.
Teen crash rates per mile driven still far exceed those of older drivers, but the studies are the latest to suggest that changes in licensing policies during the past two decades are working.
"Since 1996, when the nation's first graduated licensing system went into effect in Florida, there has been a steady, steep decline in teenagers' per capita crash rates," says Anne McCartt, IIHS senior vice president for research and lead author of the Institute's study. "We found the steepest reduction among 16 year-olds, who are most likely to be affected by graduated licensing."
A 2007 IIHS study found that between 1996 and 2005, per capita fatal and nonfatal crash rates dropped sharply for 16 year-olds and also fell for 17 and 18 year-olds (see "Teen drivers' crash rates have declined sharply since 1996," June 15, 2007). The new study extends the time period and includes more recent data about travel patterns. Institute researchers used data from government crash databases, the Census Bureau and the 1995-96, 2001-02, and 2008 National Household Travel Surveys to calculate rates of fatal crashes and police-reported crashes for drivers ages 16-19 and drivers ages 30-59. They found that per mile driven, rates of fatal crashes and police-reported crashes were much higher for teenagers than for the 30-59-year-old group during 2008 and much higher for 16-17 year-olds than for older teenagers. Lower per capita rates of fatal and police-reported crashes for 16 year-olds compared with older teenagers and adults stem from the fact that younger teenagers are less likely to be licensed and may drive less when they are.
The per capita rates of fatal and police-reported crashes among teens fell steadily from 1996 to 2012. While the largest declines were among younger teens — for example, 16 year-olds went from 33 fatal crash involvements per 100,000 people in 1996 to 9 in 2012 — all teens had much larger declines than the 30-59 year-olds, for whom fatal crashes per 100,000 people also fell, from 20 to 13. Teen drivers' crash rates per mile driven also dropped substantially and, in general, more steeply than those of the adult drivers.
The proportion of younger teen drivers' fatal crashes at night and with two or more teenage passengers also declined from 1996 to 2012. That is consistent with restrictions on night driving and young passengers that are part of GDL systems in almost all states. Previous Institute research has found that stronger restrictions on night driving are associated with larger reductions in fatal crash rates, as are laws that limit teen passengers (see "How to make young driver laws even better," May 31, 2012).
The proportion of fatally injured teenage drivers with positive blood alcohol concentrations also decreased, while it changed little for middle-age drivers.
One risk factor not addressed by GDL is speeding. The authors found that more than a third of teens' fatal crashes involved speeding, compared with less than a fifth for 30-59-year-old drivers. The percentage of fatal crashes in which drivers were speeding increased 7 percent for 16 year-olds and held more or less steady for the other ages.
In the second study, researchers found that teens are in fewer crashes when exposed to GDL, in part because they drive less and in part because they crash less often when they do get behind the wheel.
Like the IIHS analysis, this study also used data from the three most recent travel surveys. For each of the survey periods, researchers looked at the daily travel reported by people in four age groups: 16, 17, 18 and 20-24. Teenagers were classified as exposed to GDL if, at the time of the survey, their state had a GDL law with a learner phase of at least three months and either a night driving or passenger restriction in the intermediate license phase. The researchers then used the government's fatal crash data to calculate mileage-based and per capita fatal crash rates for each age group. The 20-24-year-old group was included to help control for non-GDL-related factors that influence driving, such as the economy.
The researchers conclude that GDL laws cut the per capita fatal crash rate by about a third for 16 year-olds, with half the reduction coming from a 21 percent decrease in average miles driven and half from a 17 percent drop in the rate of fatal crashes per miles driven. For 17 year-olds, GDL reduces the per capita fatal crash rate by 17 percent, with all of the reduction coming from less driving, the study finds. The reduction for 17 year-olds wasn't statistically significant.
The authors speculate that teens may drive less under GDL because it includes an extended learner phase that requires permit holders to drive with supervision, and an adult may not always be available. Intermediate restrictions also limit the hours and circumstances under which they drive. Finally, some teens may put off licensure until they are no longer subject to restrictions. Other research has shown that teens are indeed delaying driving, but the reasons in recent years seem to have more to do with economic considerations than a desire to avoid GDL (see "Teens delay licenses and drive less often; N.J. teens back restrictions for older novices," June 27, 2013).
Some have theorized that GDL would cause crash rates to go up for older teens not under the restrictions, since they might not have as much driving experience as a result. However, neither this study nor the IIHS study found any evidence that teens older than 17 have been adversely affected as states have implemented and strengthened GDL.