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Drivers on Cell Phones Clog 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.

"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 presented the study in Washington Jan. 16 during the Transportation Research Board's annual meeting.

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. The study was partially funded by the MPC.

Photo caption: Joel Cooper, a University of Utah doctoral student in psychology, demonstrates how subjects in a new study talked on a cell phone while operating a driving simulator. The new Utah study found that motorists on cell phones contribute to traffic congestion because they drive slower and are less likely to pass slow-moving vehicles. Photo by Ivana Vladisavljevic.

Martin says that, combined with Strayer's previous research, the new study shows "cell phones not only make driving dangerous, they cause delay too." One survey found that during any given daytime moment, 10 percent of U.S. drivers are using cellular phones.

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. 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. Thirty-six students 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 student spoke on a hands-free cell phone during one drive at each level of traffic density. 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.

"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. 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.

In low, medium and high traffic density, cell phone users spent 31 percent, 16 percent and 12 percent, respectively, more time following within 200 feet of a slow lead vehicle than undistracted drivers.

Strayer acknowledges that, "in itself, staying in a lane and not passing might be construed as being safer, just as driving slightly slower or having a greater following distance also could be considered safer. But if you are doing that so you can take your mind off the road and talk on the phone, that isn't safer."

Compared with undistracted 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 are talking on wireless phones at the same time, Cooper says.

Vladisavljevic already has begun computer "microsimulations" of multiple vehicles. "We saw an increase in delays for all cars in a system, and the delays increased as the percentage of drivers on cell phones increased," she says.

Strayer says it is important to show how cell phone use affects traffic because "when people have tried to do cost-benefit analyses to decide whether we should regulate cell phones, they often don't factor in the cost to society associated with increased commute times, excess fuel used by stop-and-go traffic and increased air pollution, as well as hazards associated with drivers distracted by cell phone conversations."

Martin says transportation analysts include two components – accidents and delay – when they calculate the "user costs" associated with road travel. "If we compile the millions of drivers distracted by cell phones and their small delays, and convert them to dollars, the costs are likely to be dramatic. Cell phones cost us dearly," Martin says.

A University of Utah news release on the research was issued in early January and was picked up by the Deseret Morning News in Salt Lake City, CBS, Science Daily, CNN, USA Today, ABC and other news outlets.

By Lee J. Siegel, science news specialist, University of Utah Public Relations.

Cell Phones Impact Research Published

Ivana Vladisavljevic, a research assistant at the Utah Traffic Lab, is the lead author of "Integration of Mathematical and Physical Simulation to Calibrate Car-Following Behavior of Unimpaired and Impaired Drivers," a peer-reviewed article published in World Review of Intermodal Transportation Research in 2007. Vladisavljevic earned her B.S. degree at the Department of Transportation and Traffic Engineering at the University of Belgrade, Serbia in 2004 and an M.S in civil engineering at the University of Utah in 2006. She is continuing her graduate work towards a Ph.D. at the University of Utah.

Civil Engineers Recycle Used Utility Poles into New Idea

Colorado State University (CSU) civil engineering professor and project investigator Richard Gutkowski is turning the discards of progress into the bridge systems of tomorrow. Utilizing salvaged utility poles removed as part of road expansion projects, Gutkowski and graduate student Matthew LeBorgne are recycling reusable wood into short (20-30 foot) to medium span, (40-50 foot) bridges.

Economical solution. Layering wood and concrete to create a composite bridge, the groundbreaking idea is an economical solution for low tax base communities dependent on agricultural economies and the related freight and shipping industry. Research and construction is taking place at the Structures Laboratory, part of CSU's Engineering Research Center (ERC).

Gutkowski aims to replace conventional reinforced concrete slabs, a costly system, with a composite design. Integrating an innovative cambering, or arching technique, the researchers are using tapered utility poles that will be set in alternating directions, beneath a thinner concrete slab, to attain a concave design. The concrete layer will provide compression strength and a hard-wearing surface for vehicle wheels, keeping snow and rain off the wood. The wood layer provides tensile strength by replacing the usual lower non-structural half of the concrete, its steel reinforcement and external temporary shoring with a structural wood layer that self-shores the concrete during the curing process.

Cooperation on a worldwide scale. Researchers in New Zealand, Germany, Italy and Sweden have joined forces studying long-term creep, hygrothermal effects such as the flow of moisture between materials, and the effect of humidity changes on deflection over time in composite bridge designs. In Colorado's arid climate, Gutkowski and team have been working to overcome the special properties of dry wood, which draws water from adjacent concrete, shrinking it and negatively affecting the curing process.

Although the team is utilizing a notchedshear key system – grooves cut in the wood filled with concrete when cast – interconnecting the two layers has proved to be a challenge. Because the mechanics of shrinking concrete have not been studied at relative humidity of less than 40 percent, Gutkowski has plans to examine this issue using environmental test chamber equipment at the ERC in a later phase of the project.

"Our challenge has been the need to prevent very dry wood from extracting water from the concrete in our notch connection," said Gutkowski. "We appear to have overcome that important piece of the mechanics puzzle by using additives in the concrete and sealing the wood. With that working we can better manage the immediate and long term deflection and stress behavior."

Uprooted poles spark innovative idea. The project is funded by the U.S. Department of Transportation via the Mountain-Plains Consortium within the University Transportation Centers program. In addition, Xcel Energy provided, at little to no cost, uprooted utility poles displaced as part of construction projects.

"The idea came to me when I saw them removing the poles as I passed by each day on the way to the ERC," Gutkowski recalled. "It was like a light bulb coming on."

By Lana Hoff, Director, CSU Engineering Marketing & Communications Office