"Hang up and drive."

"Nice cell phone. Hope it gives you a brain tumor."

"WWJD? He'd hang up the cell phone and try not to hit me."

As cell phone use has intensified, so has the sentiment of bumper sticker messages for multitasking drivers. Now a University of Utah study has confirmed what is obvious to most Utahns — drivers on cell phones are clogging up traffic.

Motorists on cell phones drive slower on the freeway, pass sluggish vehicles less often and take longer to complete their trips, according to a University of Utah study released Wednesday.

"At the end of the day, the average person's commute is longer because of that person who is on the cell phone right in front of them," says University of Utah psychology professor Dave Strayer, leader of the research team.

"That SOB on the cell phone is slowing you down and making you late," said Strayer.

Compared with nondistracted motorists, drivers on cell phones drove an average of 2 mph slower and took 15 to 19 seconds longer to complete the 9.2 miles. That may not seem like much but is likely to be compounded if 10 percent of all drivers — as research shows — are talking on wireless phones at the same time, researchers said.

Results showed when drivers talked on a cell phone, they made fewer lane changes, had a lower overall mean speed and a significant increase in travel time in the medium and high density driving conditions, researchers wrote in the study.

In medium and high density traffic, drivers talking on cell phones were 20 percent less likely to change lanes than drivers not on cell phones.

That may seem minor, said Joel Cooper, a doctoral student in psychology, who later this month will present the study at a Transportation Research Board meeting in Washington, D.C. The board is part of the National Academy of Sciences, National Academy of Engineering and Institute of Medicine.

"But if you have a lot of people who are not changing lanes and driving slower, this could substantially reduce traffic flow," Cooper said.

It's worse than that, said detective Jeff Bedard of the Salt Lake Police Department.

"Talking on the cell phone ranks up there with driving tired or driving while impaired," he said. "It may be that nine out of 10 times nothing happens, but on that one occasion where your attention is diverted is where you cause or are involved in an accident."

An insurance company survey estimated 73 percent of wireless users talk while driving. Another survey found that during any given daytime moment, 10 percent of drivers nationally are using cell phones.