WASHINGTON — From Jeannie Harrison’s perspective, the social lives of most teenagers tend to revolve around their cell phones — even when they are behind the wheel.

“People don’t want to be inaccessible for even 15 minutes driving up the street,” said Ms. Harrison, 19, a sophomore at Marshall University in Huntington, W.Va. “They’re so used to being accessible all the time.”

Targeting inexperienced motorists, several states have passed laws during the past five years restricting cell phone use by teenage drivers.

But an insurance industry study being released today that looked at whether teenagers are ignoring such restrictions contends enforcement and parental influence are just as important as new laws.

The Insurance Institute for Highway Safety studied North Carolina’s law, enacted in 2006, which fines motorists under age 18 who are caught using a cell phone.

Researchers who watched as high school students left school found that teenage drivers used their cell phones at about the same rate both before and after the law took effect. In South Carolina, which does not have a similar restriction, cell phone use by teenage drivers was about the same for both periods studied.

A separate phone survey of North Carolina parents and teenagers showed widespread support for their state’s law, but more than three in five reported that enforcement was rare or nonexistent.

“Cell phone bans for teen drivers are difficult to enforce,” the institute’s senior vice president for research and an author of the study, Anne McCartt, said. “Drivers with phones to their ears aren’t hard to spot, but it’s nearly impossible for police officers to see handsfree devices or correctly guess how old drivers are.”