For generations, teenagers have been the most dangerous drivers on the road, crashing almost four times more often than older drivers. A study quantifies for the first time in a decade how their risk of a fatal crash multiplies when they have other teenagers in the car.

It increases by almost half when a 16- or 17-year-old driver has one teenage passenger; it doubles with two teen passengers; and it quadruples with three or more young passengers.

Using federal fatality statistics, the American Automobile Association Foundation for Traffic Safety provided that data that will support parents who have forbidden their teenage children from driving with other teenagers.

"We know that carrying young passengers is a huge risk, but it's also a preventable one," said AAA foundation President Peter Kissinger.

The AAA study is the latest of three recent reports to raise concerns about teenage drivers. The Governors Highway Safety Association reviewed preliminary data from the first six months of last year, finding a slight increase in the number of fatal crashes involving 16- and 17-year-old drivers. The governors' group said if the trend continued, 2011 would reverse a recent trend of declining teenage fatalities.

In another study, National Highway Traffic Safety Administration last month said its research found that drivers under the age of 24 were much more likely than more mature drivers to send and receive text messages while driving.

Read more from the Washington Post.

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