University of Utah psychology professor Dave Strayer, psychology doctoral student Joel Cooper, doctoral student in civil and environmental engineering Ivana Vladisavljevic and Peter Martin, director of the University of Utah Traffic Lab, conducted the study using a PatrolSim driving simulator -- in which a person sits in a driver's seat equipped with gas pedal, brakes, steering and displays from a Ford Crown Victoria police patrol car, while traffic scenes are projected on three screens around the driver.

The study involved 36 University of Utah psychology undergraduates, who drove through six, 9.2-mile-long freeway scenarios corresponding to freeway speeds of 70 mph to 40 mph.

"Results indicated that when drivers conversed 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," the researchers said in a statement.

Cooper is scheduled to present the study Jan. 16 at the Transportation Research Board's annual meeting in Washington.