The more restrictions imposed, the greater the reduction.
Examples include a waiting period before a young driver is eligible to move from a learner's permit to an intermediate license, restrictions on driving at night, required hours of supervision by an adult driver and limits on the number of passengers a teenage driver can have.
States with such restrictions as part of strong graduated driver's licensing programs showed declines in fatal crashes involving 16-year-olds, according to a study being released Monday by Johns Hopkins Bloomberg School of Public Health in Baltimore.
"We already knew that the programs reduced crash rates of young drivers, but we didn't know which programs were most effective in reducing risk," said Susan P. Baker, a professor at the school. From the study, "it is clear that more comprehensive programs have the greatest effect," she said.
Traffic accidents are the leading cause of death for teenagers. Federal figures show that 16-year-old drivers were involved in 957 fatal crashes that killed 1,111 people in 2004. Those crashes resulted in the deaths of 399 16-year-old drivers and 385 16-year-old passengers.
States put limits on new drivers, but the rules vary. Researchers said that by the end of 2004, 41 states and the District of Columbia had programs that included a learner's permit with supervised training, an intermediate period with a limited amount of unsupervised driving and a final stage without restrictions.
The study based its analysis on programs with these requirements:
—a minimum age of 15 1/2 for earning a learner's permit.
—a waiting period of at least three months after getting a learner's permit before applying for an intermediate license.
—a minimum of 30 hours of supervised driving.
—a minimum age of 16 for obtaining an intermediate state license.
—a minimum age of 17 for full licensing.
—driving restrictions at night.
—a restriction on carrying passengers.
The study found that such programs reduced fatal crashes for 16-year-old drivers by an average of 11 percent.
When the researchers compared states with five program components to states without a program, they found an 18 percent reduction in fatal crashes involving 16-year-old drivers.
Programs with six or seven components were linked to a 21 percent reduction, showing the added benefit.
Researchers found a 16 percent to 21 percent reduction in fatal crashes when the programs included an age requirement, a 3-month wait before applying for an intermediate license, nighttime driving restrictions and either 30 hours of supervised driving or passenger restrictions.
"This study strongly underscores the effectiveness of graduated licensing laws," said Nicole Nason, head of the National Highway Traffic Safety Administration. "To states searching for solutions to the tragic problem of fatal crashes involving teenagers, it provides extremely valuable new information."
Researchers used data from 1994-2004 collected by the agency and the Census Bureau. They evaluated graduated licensing programs and fatal crashes in 36 states with the licensing programs and seven without the restrictions.