Girls speed up regardless of who the passenger is, the study also showed.
KNIGHT RIDDER NEWSPAPERS
WASHINGTON -- A teenage boy driving with another teenage boy is more likely to speed and tailgate than when he drives alone. But put a teenage girl in the car, and he'll slow down.
The fix isn't so simple for teenage girl drivers, however, according to a federal study released Friday. Girls drive faster whether the passenger's a guy or girl than they do when they drive solo.
The study, by the National Institute of Child Health and Human Development, found that a quarter of teens with male passengers drove at least 15 mph over the test's 40-mph speed limit. Just 10 percent of teens drove that fast when they were alone.
Teen males with teenage male passengers were also more likely to tailgate, leaving an average of about one car length less room in front of them at 40 mph than when they drove alone.
The study included 471 teenage drivers on public roads.
The perils of teen passengers don't surprise Russ Rader, a spokesman for the Insurance Institute of Highway Safety, an insurer-funded research group that seeks to reduce accident rates.
"When you have a teen passenger in the vehicle with a teen driver, the risk of a crash is twice as high," Rader said. "If you have two or more teen passengers in a vehicle, the risk can be five times as high."
The study found that when male teens drove dangerously, 22 percent had male passengers and only 6 percent had female passengers.
All but 17 states restrict the number and/or ages of passengers that new drivers can carry.
According to the Insurance Institute for Highway Safety, the states that don't restrict passengers for new drivers are Arizona, Arkansas, Florida, Idaho, Iowa, Kentucky, Louisiana, Kansas, Michigan, Minnesota, Mississippi, Missouri, Nebraska, North Dakota, Ohio, Pennsylvania and South Dakota.
Rader said parents need to enforce those rules with their kids. States often don't, unless the driver is stopped for another reason.
"Making sure that teens are not driving other teens, and not riding with other teens in the first year of driving, is very successful" in preventing accidents, he said.