Unsafe behind the wheel? With car crashes the leading cause of death for teenagers, states are placing greater restrictions on young drivers.

• Author: Zernike, Kate

It's long been a rite of passage for American teens: getting a driver's license and going for a spin with as many friends as can cram into the car.

But with mounting evidence that teenagers are at high risk for car accidents, more states are legislating away that carefree cruise, imposing tougher restrictions on how and when teens can drive--and who they can take along for the ride.

Fifteen states and Washington, D.C., now prohibit unsupervised teenagers in their probationary period from driving with another teenager, and 44 states forbid them from driving with more than one teen. In South Carolina, teenagers can't drive after 6 p.m. in winter (8 p.m. in summer), and in Idaho, they're banned from driving from sundown to sunup.

In New Jersey--which has long had the nation's highest licensing age, 17-lawmakers have pushed further. New Jersey now requires first-year drivers under 21 to attach a red decal to their license plates to make it easier for the police to enforce an 11 p.m. curfew and passenger restrictions. And a bill now before the state legislature would require parents of teen drivers to complete a driver education course.

Safety campaigners point to studies showing that teen driving laws have significantly reduced traffic deaths.

But others, like Jeffrey Nadel, the 19-year-old president of the National Youth Rights Association, take issue with driving restrictions.

"These laws are blatantly discriminatory," says Nadel. He also argues they may have an unintended downside:

A 2011 study in The Journal of the American Medical Association suggests that restrictions for young drivers may lead to a higher incidence of fatal accidents for 18-year-olds, possibly because they didn't get enough practical driving experience earlier.

Lawmakers around the nation, however, say the restrictions are necessary in light of some alarming statistics: Car crashes are the leading cause of death for teenagers, who have a crash rate four times higher than that of older drivers.

Texting Behind the Wheel

Studies have shown that teens tend to overrate their driving skills and underrate risks on the road. They also have more trouble multitasking--talking to friends, listening to the radio, and texting are particularly hazardous. Teenage drivers' risk of a crash increases 44 percent with one teenage passenger and quadruples with three or more. Two-thirds of teen passenger deaths happen in a car driven by another teen.

Efforts to address the dangers of teen...