"If you put a 20-year-old driver behind the wheel with a cell phone, their reaction times are the same as a 70-year-old driver who is not using a cell phone. It's like instantly aging a large number of drivers," says David Strayer, a University of Utah psychology professor and principal author of the study.

Frank Drews, as assistant professor of psychology and study co-author, adds: "If you want to act old really fast, then talk on a cell phone while driving."

The new study by Strayer and Drews was published in this winter's issue of Human Factors, the quarterly journal of the Human Factors and Ergonomics Society.

The study found that when 18- to 25-year-olds were placed in a driving simulator and talked on a cellular phone, they reacted to brake lights from a car in front of them as slowly as 65- to 74-year-olds who were not using a cell phone.

The elderly drivers, meanwhile, became even slower to react to brake lights when they spoke on a cell phone. But the good news for elderly drivers was that their driving skills did not become as bad as had been predicted by earlier research showing that older people performing multiple tasks suffer additional impairment due to aging.

The study found that drivers who talked on cell phones regardless of whether they were young or old were 18 percent slower in hitting their brakes than drivers who didn't use cell phones. The drivers chatting on cell phones also had a 12 percent greater following distance an effort to compensate for paying less attention to road conditions and took 17 percent longer to regain the speed they lost when they braked.

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1-Feb-2005