Talking on a cellphone while driving slows down traffic, University of Utah researchers reported Wednesday.

"That SOB on the cellphone is slowing you down and making you late," psychology professor Dave Strayer said in a news release. "At the end of the day, the average person’s commute is longer because of that person who is on the cellphone right in front of them."

Drivers talking on cellphones are less likely to change lanes to pass a slow car, a new study suggests.
(CBC)

Using a computer simulation, where 36 students "drove" a car on a section of highway where conditions mimicked those on a major Salt Lake City route, the researchers found that the students talking on a hands-free cellphone took 15 to 19 seconds more for the 15-kilometre trip and were less likely to change lanes to overtake a dawdling driver.

"We designed the study so that traffic would periodically slow in one lane and the other lane would periodically free up," said researcher Joel Cooper, a doctoral student in psychology. "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 time differences between drivers on phones and those not on phones during the simulated car trip were relatively small.

But researcher and engineering graduate student Ivana Vladisavljevic ran simulations to see how changing the proportion of drivers talking on phones affected traffic flow.

"We saw an increase in delays for all cars in a system, and the delays increased as the percentage of drivers on cellphones increased" from zero to 25 per cent, she said.

Citing statistics from other sources, the university release said that there are an estimated 240 million U.S. cellphone subscribers and nearly three-quarters of them use their phones while driving. Another study estimated that at any given time in the day, 10 per cent of U.S. drivers are on their cellphone.

Strayer's previous research showed that cellphone drivers are more likely to have an accident, their reaction times are slower and talking on a cellphone impairs drivers as much as having a 0.08 per cent blood alcohol level, which defines drivers as drunk in many jurisdictions.

But that prior research did not look at how traffic flow was affected. Strayer worked with engineering professor Peter Martin, director of the University of Utah traffic lab, to study the traffic effects.

Cooper is set to present the research on Jan. 16 at the annual meeting of the U.S. Transportation Research Board.