Drivers on cell phones congest traffic

Motorists who talk 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 that suggests drivers on cell phones congest traffic.

“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.”

“If you talk on the phone while you're driving, it's going to take you longer to get from point A to point B, and it's going to slow down everybody else on the road,” says Joel Cooper, a doctoral student in psychology.

Cooper is scheduled to present the study in Washington on Wednesday, Jan. 16 during the Transportation Research Board's annual meeting. The board is part of the National Academies, parent organization of the National Academy of Sciences, National Academy of Engineering and Institute of Medicine.

Cooper and Strayer conducted the study with Ivana Vladisavljevic, a doctoral student in civil and environmental engineering, and Peter Martin, an associate professor of civil and environmental engineering and director of the University of Utah Traffic Lab.

Martin says that, combined with Strayer's previous research, the new study shows “cell phones not only make driving dangerous, they cause delay too.”

In recent years, Strayer's research group has published studies showing that:

• Hands-free cell phones are no less dangerous while driving than hand-held cell phones because the conversation itself is the major distraction.
• When young adults talk on cell phones while driving, their reaction times become as slow as reaction times for senior citizens.
• Drivers talking on cell phones are as impaired as drivers with the 0.08 percent blood alcohol level that defines drunken driving in most states.

Highway statistics suggest drivers on cell phones are four times more likely to be in an accident, and Strayer's earlier research suggests the risk is 5.36 times greater.

The Cellular Telecommunications and Internet Association claims 240 million U.S. subscribers in a nation of 303 million people. 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 U.S. drivers are using cellular phones.

The researchers note that 50 countries have adopted laws banning handheld phones while driving. But they say hands-free phone conversations are distracting, “thus, the majority of current regulation appears to be misguided.”

The earlier studies found that cell phone users follow at greater distances, are slower to hit the brakes and are slower to regain speed after braking. But such research didn't examine how traffic efficiency is influenced by individual cell phone users.

That led to Strayer and Martin discussing the possibility of using computers to simulate numerous individual cell phone users' driving behavior and thus overall traffic. So their doctoral students – Cooper and Vladisavljevic – conducted the new study as a step toward an eventual computer “microsimulation” of numerous drivers and vehicles.

The new study used a PatrolSim driving simulator. A person sits in a front seat equipped with gas pedal, brakes, steering and displays from a Ford Crown Victoria patrol car. Realistic traffic scenes are projected on three screens around the driver.

The new study involved 36 University of Utah psychology undergraduates. Each student drove through six, 9.2-mile-long freeway scenarios, two each in low, medium and high density traffic, corresponding to freeway speeds of 70 mph to 40 mph. Each 9.2-mile drive included 3.9 miles with two lanes in each direction and 5.3 miles with three lanes each way. Traffic speed and flow mimicked Interstate 15 in Salt Lake City.

Each student spoke on a hands-free cell phone during one drive at each level of traffic density, and did not use a cell phone during the other three drives. A volunteer on the other end of the phone was told to maintain a constant exchange of conversation.

The drivers were told to obey the 65-mph speed limit, and use turn signals. That let participants decide their own speeds, following distances and lane changes.

“We designed the study so that traffic would periodically slow in one lane and the other lane would periodically free up,” Cooper says. “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.”

“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 wrote.

• In medium and high density traffic, drivers talking on cell phones were 21 percent and 19 percent, respectively, less likely to change lanes (roughly six lane changes per 9.2-mile drive versus seven or eight lane changes by drivers not on cell phones).

That may seem minor, “but if you have a lot of people who are not changing lanes and driving slower, this could substantially reduce traffic flow,” Cooper says.