WASHINGTON — The rate of deadly car crashes among the nation's youngest, most accident-prone drivers decreased sharply in the decade after most states enacted laws limiting their access to a driver's license, a new study shows.

Nationally, the death rate involving 16-year-old drivers fell 26 percent between 1993 and 2003, as 46 states and the District of Columbia enacted graduated-licensing laws that allow fewer 16-year-olds to drive, according to the study released yesterday by the Insurance Institute for Highway Safety.

Washington State's fatality rates for 16-year-olds are too low to make comparisons; however, the overall collision rate for 16-year-olds dropped by nearly half in the first 2½ years after restrictions took effect in July 2001.

The institute also credits restrictions in British Columbia for an estimated 16 percent overall crash reduction among 16-year-old drivers in the province over the decade. In Oregon, where a law took effect in March 2000, injury and fatality crashes declined 37 percent for 16-year-old drivers between 1998 and 2003, according to state Department of Transportation figures.

Among 16-year-olds who have full driving privileges, the rate of fatal crashes hasn't fallen nationally, and it remains higher than that of any age group. Researchers said the difference between the two groups points to the effect of the new laws, which keep most 16-year-olds from receiving unrestricted licenses and are intended to curb risky practices, such as carrying teenage passengers and driving at night.

The study shows that "withholding a license is going to improve the crash picture among 16-year-olds," said Susan Ferguson, senior vice president for research at the institute and an author of the study. "That's a success story, because the fewer of them who drive, the fewer of them who die."

The higher crash and fatality rates for teenagers in their first year behind the wheel have prompted highway-safety advocates to fight for laws that prevent them from driving unsupervised, at least until they turn 17. Sixteen-year-olds are four times more likely than adult drivers to become involved in a crash and three times as likely to die in one, national statistics show.

Motorists are at the greatest risk during their first year of driving — with high speed, driver error and multiple passengers contributing to crashes, previous research cited by the Insurance Institute shows.

Although the rules vary by state, graduated-licensing programs extend the learner's period, the time that teenagers must drive with an adult in the car. Further, they limit driving under conditions linked to crashes. The first graduated-licensing program was introduced in Florida in 1996. By 2003, 47 jurisdictions had such programs.

In Washington state, the annual collision rate for 16-year-olds dropped from 1,746 to 967 collisions — a 45 percent improvement — after the 2001 restrictions, according to a chart from the Washington Traffic Safety Commission.

"I am surprised that there was this much of a drop," commission spokeswoman Jonna VanDyk said.

She said parents initially weren't very aware of the rules — and teens had no incentive to tell them — but the commission in the past two years has been "working that law a bit harder." The effort included radio and television advertising by State Farm Insurance and state-funded training videos for police, she said.

The commission also funded overtime pay for police to patrol around high schools, she said. During a crackdown in Lacey, students spread the word by cellphone for passengers to get out of cars. "The doors started opening, and they all started flying in different directions," VanDyk said.

Washington drivers ages 16 and 17 may not carry passengers younger than 20 years old, except immediate family, during the first six months after being licensed. No more than three passengers may ride along, except family, after that. Restrictions are lifted if a young driver goes one year without a collision or traffic offense.

According to the study, more than one-fourth fewer 16-year-old U.S. motorists died in car crashes in 2003 than did in 1993 on a per capita basis. That is despite an 18 percent increase in the number of 16-year-olds in the nation, the study found. At the same time, the percentage of fully licensed 16-year-olds declined — from 42 percent in 1993 to 31 percent in a decade.

Also striking, Ferguson said, was a 39 percent drop in fatal crashes involving a 16-year-old driver carrying other teenage passengers. "The probability of being in a crash increases with each additional [teenager] in the car," she said. The figures show that "there's a fundamental change in the way young passengers are being transported."

Seattle Times staff reporter Mike Lindblom contributed to this report.