There is a large body of evidence on the dangers of inattention and distraction when driving, including using cellphones, says Amanda Lenhart, senior research specialist with Pew. Some studies indicate that talking on a cellphone is more distracting than talking to a passenger in the car, she says.

She and researchers at the University of Michigan did focus groups with teens about the issue. Some wouldn't acknowledge the danger of texting or talking on the cellphone while behind the wheel, but many thought it was unsafe and wouldn't do it. They also object when a driver does it when they are a passenger in the car. "We heard from many teens that it's their parents who are texting or talking on the cellphone when they are driving."

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