Drivers who talk on cell phones end up driving like elderly people, with slower reaction times and a tendency to miss what is right in front of them, U.S. researchers said on Wednesday.

Even when they used “hands-free” devices, young drivers who normally have the quickest reflexes drove like 70-year-olds, the team at the University of Utah found.

“If you want to act old really fast, then talk on a cell phone while driving,” said Frank Drews, an assistant professor of psychology who worked on the study.

“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,” added David Strayer, a psychology professor who led the study and who has been studying the effects of cell phone use on driving for years.

Writing in the journal Human Factors, Strayer’s team said they tested people aged 65 to 74 against drivers aged 18 to 25.

Preliminary tests showed older people were slower in processing information, which is normal and expected.

Then the volunteers used a driving simulator with dashboard instruments, a steering wheel and brake and gas pedals, surrounded by three screens showing freeway scenes and traffic.

An image showed a car in front repeatedly hitting its brakes.

Each volunteer drove four simulated 10-mile freeway trips lasting about 10 minutes each, talking on a cell phone with a research assistant during half the trips and driving without talking the other times.

Only hands-free devices were used.

The older drivers hit the brakes more slowly to avoid the car in front, tended to hit the brakes twice, took longer to regain speed and had a greater following distance.

Cell phone use made older people drive even worse and younger drivers act like elderly drivers.

“Once drivers on cell phones hit the brakes, it takes them longer to get back into the normal flow of traffic,” Strayer said. “The net result is they are impeding the overall flow of traffic.”

Braking time slowed 18 percent when young or elderly drivers used a cell phone, the researchers found. Chatting on the telephone caused a 12 percent greater following distance, apparently an effort to compensate for paying less attention to the road.

But that tactic didn’t always work.

“There was also a twofold increase in the number of (simulated) rear-end collisions when drivers were conversing on cell phones,” the researchers wrote.