People using mobile phones while driving contribute to traffic congestion, according to a University of Utah study. Regardless of whether they use a handset or Bluetooth, the conversation itself causes motorists to drive slower on the freeway and to be less likely to pass slower-moving vehicles.

 And that means it takes longer to get from point A to point B, or up to an extra 19 seconds per 9-mile trip. That doesn’t sound like a lot, but UU psychology professor and leader of the research team, Dave Strayer, says that compounds significantly when multiplied by the 10 percent of US drivers that are talking on a cell phone while driving at any given moment.

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

And costing you about $13 for every hour delayed, on average.

The study was conducted with 36 students using a PatrolSim driving simulator. The subjects navigated a course designed to mimic the traffic flow of a 9.2-mile stretch of a Salt Lake City freeway.

“We designed the study so that traffic would periodically slow in one lane and the other lane would periodically free up,” said Joel Cooper, a doctoral student in psychology, who will present the study in Washington on Wednesday, Jan. 16 at the Transportation Research Board’s annual meeting.

“It created a situation where progress down the road was clearly impeded by slower moving vehicles, and a driver would benefit by moving to the faster lane, whether it was right or left.”

The researchers argue that while the differences in speed and willingness to change lanes were small, the extra time it takes to complete a trip can have a domino effect on traffic. "If you get two or three people gumming up the system," said Strayer, "it starts to cascade and slows everybody’s commute.”

Driving slower isn’t necessarily safer either. The researchers note that if a cell phone conversation is the reason a person is driving slower, then the reduced speed (about 2 miles per hour slower on average) isn’t really safer.

Earlier research from this same group found that hands-free calling was no safer than using handsets, as the conversation itself was the distraction. Young drivers exhibited reaction times as slow as senior citizen drivers, and motorists using cell phones are considered as impaired as a person with a blood alcohol level of 0.08.