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Summer 2002

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In a Roundabout Way

Illustration by Valerie Williams

In a Roundabout Way
UMaine engineer takes to the road to improve safety

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Ask Per Gårder about traffic safety and he'll give you a roundabout answer.

The University of Maine professor of civil engineering has been a strong advocate for modern roundabouts which, he is quick to point out, bear little resemblance to yesterday's rotaries. His research on accident rates, personal injuries and traffic flow at 23 intersections in seven states, including Maine, has convinced him that highway engineers in the United States can use roundabouts to save lives and reduce congestion.

Roundabouts may look like traditional rotaries to the untrained eye. The difference is they are designed with specific geometric angles, slowing entering traffic to 15-25 miles per hour, instead of the 35 miles per hour or more of rotaries. New roundabouts also offer better visual cues, such as signs and well-marked islands at exits and entrances that help drivers maintain a comfortable, orderly flow.

An analogy to flowing water is fitting for the roundabouts advocated by Gårder, who once considered studying hydraulics in college. Rather than working with plumbing systems that channel water molecules through networks of pipes and valves, he focuses on systems of roads and intersections that safely and efficiently get vehicles from one place to another.

A bus route
For his master's thesis at the Lund Institute of Technology in Sweden, Gårder developed new ways to design networks of public bus routes. A drawback to many public transportation systems, he says, is their tendency to funnel all riders downtown. If a person needs to go from one suburb to another, the bus ride can take much longer than necessary.

"When everybody works in the central business district, that's good for commuting. But nowadays, when people live in one outskirt and work in another, it is difficult for public transportation to meet people's needs. That's one of the reasons that people don't use public transportation in the United States," he says.

Even more important for Gårder is reducing the number of accidents that take about 42,000 lives and cause about 1.6 million disabling injuries annually in the U.S. Together with the 25 million other traffic accidents that don't cause death or injuries, the total bill comes to more than $100 billion.

At about 16 deaths per 100,000 people, the U.S. has one of the worst records for traffic fatalities in the developed world, he says. With an average of 200 traffic-related deaths per year, Maine is near the national standard.

"Northern states like Maine do slightly better than Southern states, but if we compare to the United Kingdom, Norway or Sweden, they are all slightly below six fatalities per 100,000 people," Gårder says.

Rumbling along
Shortly after he came to UMaine in 1992, Gårder made a significant contribution toward improved safety on U.S. highways. Working with former civil engineering professor John Alexander, he demonstrated that highway rumble strips, lines etched into the pavement just outside the travel lanes, could save lives. The noise of tires hitting rough pavement can avert one of the most significant problems on interstate highways — drivers who doze off at the wheel and drift off the road. Before rumble strips were installed, nearly half of all fatal crashes on Maine's interstates were caused by people falling asleep.

Gårder and Alexander did not invent the technology. Some states had been experimenting with rumble strips since the 1950s. However, their project was the first academic study of this simple life-saving technology in the country and has been credited with spurring more widespread use.

Their results showed what engineers consider an astounding cost/benefit ratio of more than 1 to 100, meaning that for every dollar invested, more than $100 would be saved in property damages, healthcare expenses and other costs.

"Our first paper was refused by the reviewers because they thought that no measure would ever have a benefit cost ratio of 100 or above," says Gårder. However, a new federal report on rumble strips cites the same results, confirming that Gårder and Alexander were right.

The Maine Department of Transportation published two reports on rumble strips and began installing them along I-95 in 1994.

"For a couple of years after that, I was getting e-mails and phone calls once or twice a week from people who had been awakened by the rumble strips," says Gårder. "They were thanking me for saving their lives."

While the benefits are clear, every technology has some negative consequences. Rumble strips are no exception. In 2000, a motorcyclist reported that by moving across a rumble strip to stop along the highway, she lost control and crashed.

Gårder takes such possibilities seriously. He also points to the overwhelming evidence of lives saved and property damage reduced. In fact, since rumble strips were installed, the number of accidents that have been linked to sleepy drivers on I-95 has gone down about 37 percent.

While rumble strips have been well accepted, roundabouts are another story. Proponents in engineering firms, universities and state transportation departments are touting the benefits, but the public is not so sure. Newspaper accounts of public meetings in Florida, California and Illinois reflect citizen discomfort with roundabouts that some view as "an accident waiting to happen."

Gårder suggests that the American aversion to roundabouts is the result of experience with poorly designed rotaries. "In the United States, we had a lot of circular intersections built in the 1920s and 1930s," he says. "Some of them worked reasonably well, and some of them were too big and designed for speeds that are too high."

States began constructing modern roundabouts in the early 1990s. With some design assistance from Gårder, the Maine Department of Transportation opened one at the intersection of routes 202 and 237 in Gorham in 1997. The goal of the project was to reduce the accident rate and waiting times for the 13,000 vehicles that travel through that junction on an average day.

Gårder's evaluation after only one year of operation showed that the roundabout was working as planned. He found that the accident rate had dropped from 1.36 per million vehicles to 0.8. Even better, personal injuries were down. Three accidents had occurred at the roundabout, but none caused injuries. They were all sideswipe accidents. Broadside or head-on collisions that are more common at traffic lights and stop signs tend to be far more dangerous.

On the road
The Maine experience is not unique. In Florida, Vermont, Colorado and other states, roundabouts have performed with similar results. In 2001, Gårder and colleagues at Ryerson Polytechnic University in Toronto and the Insurance Institute for Highway Safety published a landmark study based on accident reports for 23 roundabouts in seven states. They compared accidents before and after the roundabouts were constructed.

Just as important, they used statistical techniques to account for variability in traffic flow and what traffic engineers call a randomness factor. Stated simply, a small number of accidents can happen randomly anywhere because behavior is unpredictable. Drivers fall asleep, have heart attacks and drive drunk. Animals wander onto roads. No intersection or highway is foolproof.

"If you don't take randomness into account, you end up with even better numbers for the roundabout," says Gårder. "But taking it into account makes it a more complicated but more honest analysis."

Their results showed that the 23 roundabouts achieved a 40 percent reduction in all accidents, an 80 percent reduction in injury-causing accidents and a 90 percent reduction in fatalities. The strength of their case earned the paper a prestigious award from the Transportation Research Board, as one of the four best research papers out of 2,000 submitted in 2001.

"My strong belief is that fewer people are seriously injured at a roundabout than at any traffic signal you will ever have," says Gårder. "The reason is that the roundabout reduces the speed of almost everyone to about 15–20 miles per hour. At a traffic signal, a lot of people will not reduce their speed, especially when the light is yellow. The typical person believes that traffic signals are perfectly safe because when it's red, people stop and when it's green, they go."

Despite their demonstrated safety, Gårder wouldn't build roundabouts at all intersections now controlled by stop signs or signals. However, where roundabouts would be particularly useful is on rural highways at the outskirts of small towns and villages.

"We have 45–50 mile per hour highways going through towns without changing geometric standards," he explains. "We have a lot of accidents in these small towns, partly because people do not slow down. They continue to drive at 45 miles per hour, even if the signs say 25 miles per hour."

Roundabouts would be an effective way to slow traffic down where rural highways enter developed areas, Gårder says. They also could offer drivers equal access to the business district or a downtown bypass. Giving through traffic the chance to stay out of downtowns would help reduce the congestion for which some small communities have become famous.

"We should not accept people being killed for reasons that are avoidable. Traffic fatalities are not fully avoidable, but we could reduce the number a lot," says Gårder.

by Nick Houtman
Summer 2002

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