CHICAGO (AP) _ Restricting teen-agers' driving privileges until they prove their ability behind the wheel can dramatically reduce crashes involving 16-year-olds, according to studies of ``graduated license'' laws in Michigan and North Carolina.
The programs may work by simply limiting the amount of time teen-agers spend driving, or by less obvious means, such as rewarding safe driving with more privileges. The studies said both may help explain the programs' success.
Traffic accidents are the leading cause of death among U.S. teens, and the youngest drivers have the highest likelihood of crashing. In the past four years, 34 states and Washington, D.C., have enacted graduated licensing programs, researchers said.
Michigan and North Carolina enacted theirs in 1997. The studies compared crash statistics there in 1996 and 1999.
In Michigan, 16-year-olds were 25 percent less likely to get into a car crash in 1999, said researchers led by Jean Shope of the University of Michigan.
In North Carolina, the risk of a crash dropped 23 percent among 16-year-olds. Nighttime crashes involving 16-year-olds declined by 43 percent, and fatal crashes plunged 57 percent.
``In North Carolina, during 1999 alone, the result was dozens of lives preserved, thousands of injuries prevented, and millions of dollars saved,'' Robert Foss and colleagues at the University of North Carolina's Highway Safety Research Center wrote in Wednesday's Journal of the American Medical Association.
North Carolina requires motorists who are at least 15 to drive with an adult for the first year of their license. Teens who have no traffic violations in the final six months and pass a road test may obtain a less restrictive license, allowing unsupervised daytime driving. They then must complete at least six continuous months of driving with no traffic violations to get a full, unrestricted license. Michigan has similar restrictions.
In an accompanying editorial, researcher Anne T. McCartt called the results encouraging but said further studies are needed to identify which restrictions are most effective. McCartt works for the highway safety research firm Preusser Research Group of Trumbull, Conn.