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IIHS News | August 31, 2006Subscribe

Teen drivers' crash rates go down significantly under provisions of California's graduated licensing law

ARLINGTON, Va. — The main finding of a new evaluation of graduated licensing is a 23 percent overall reduction in the per capita crash involvement rate of 16-year-old drivers in California. Crashes went down more in the high-risk situations specifically addressed by graduated licensing — nighttime crash rates went down 27 percent, and crash rates with teen passengers decreased 38 percent. The study was conducted by the Insurance Institute for Highway Safety.

"More evidence that graduated licensing is reducing crashes," says Susan Ferguson, Institute senior vice president for research.

California legislators were among the first in the nation to enact graduated licensing, which took effect in 1998. The law increased the learner's permit period and required parents or guardians to certify that learners get at least 50 hours of practice. Once licensed, 16 year-olds still are restricted. They may not drive unsupervised at night or any time with teen passengers.

Benefits of this law aren't being achieved by postponing the crash problem until 16 year-olds get a little older. That is, the law isn't shifting high crash rates from 16-year-old beginners to 17 year-olds, whose crashes also declined after graduated licensing. Nor are crashes going up among beginners driving alone, despite concern that the passenger restriction would increase risk by forcing groups of teens to travel in separate vehicles to the same destination. The Institute found reductions in crashes in which beginners drove alone, went as passengers, etc.

"We conducted our analyses several ways, all of which revealed positive results. So we know the law is successful," Ferguson says.

Similar laws that phase in driving privileges for beginning teens over time have been enacted in most states, but the requirements vary. Multiple studies of the laws in states other than California also reveal benefits, including fatal crash reductions. An exception is a study published in 2003 by the California transportation department, which found no overall effects of graduated licensing.

This result is out of line not only with findings in other jurisdictions but even with results of two other evaluations of the California law that were conducted before the Institute's analyses. One of these concluded that graduated licensing reduced the per capita crash rate of 16-year-old drivers by 28 percent. The other, using a slightly longer study period, reported a 17 percent reduction. Both studies were published in 2004.

The Institute's new analyses "aren't all that different from the approach used by the researchers at the California transportation department, who found no effects. We used time series, just as they did. It's a routine statistical method, but in this case the California researchers didn't use time series to factor in all of the various trends in crashes of 16 year-olds that were occurring before the graduated licensing law took effect. For example, they didn't take into account some of the seasonal variations in the data," Ferguson explains. "Once we took these other factors into account, the benefits of graduated licensing were clearly revealed."

California may be reaping even greater benefits since the Institute's study was conducted because the law itself has been strengthened. The new law has raised the minimum age for a learner's permit from 15 to 15-1/2, started the nighttime restriction at 11 pm instead of midnight, and extended passenger restrictions to cover the first year of licensure instead of the first 6 months. These provisions make this one of the nation's strongest graduated licensing laws.

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