OREGON STATE UNIVERSITY

Urban traffic congestion linked to "arterial" access

08/11/2000

CORVALLIS, Ore. - Many of the "arterial" roads in America's urban areas are not functioning properly due to the poor location or design of access roads, experts say, and steps are urgently needed to recognize the seriousness of this problem and take steps to address it.

Some of that work is already underway in Oregon.

Recent research by engineers at Oregon State University, in collaboration with the Oregon Department of Transportation, has helped inject modern traffic science into decisions that often in the past were based on arbitrary estimates or may not have adequately considered our exploding traffic levels.

This issue is a concern of local businesses, developers and the traveling public, said Bob Layton, a professor in the OSU Department of Civil, Construction and Environmental Engineering. The need is to balance ready access to businesses with driving efficiency, safety and convenience. And the significance of the problem, Layton said, is the reason that experts from all over the United States will be meeting Aug. 13-16 in Portland, Ore., to consider the problems in a conference titled "Taking Access Management into the New Millenium."

"Uncontrolled access to arterial streets can cause the traffic flow to break down, congestion to become almost intolerable and local businesses to suffer," Layton said. "As traffic engineers we've now developed some good tools and knowledge to help address this problem, but we have to convince both travelers and business owners that access management is good for everyone."

At the moment the effective functioning of arterial streets, which are the major connection between freeways and residential streets, are the critical link in our automotive transportation systems, Layton said.

"It's essential that we have an integrated surface street system with all types of roads, ranging from residential streets to high capacity freeways, that move traffic with safety, speed and economy," Layton said. "Right now the biggest concerns are with the urban arterials, and how well they operate is dramatically influenced by how access to them is managed."

Arterial streets in which access locations, spacing and design are not managed can result in delays, congested traffic, accidents and uneconomic public investment.

There are ways to address this, Layton said, such as controlling driveway access from stores or homes, improving the design of that access, installing medians to control where drivers make left turns, creating an adequate supporting surface street system, and providing appropriate turn lanes.

The impacts are serious. When a driver slows to about five miles per hour to turn into a driveway, while the rest of the traffic on the road is moving at 45 miles per hour, studies show the accident potential goes up by about 200 times. Every additional stop a driver has to make per mile raises fuel consumption by 20 percent and exhaust emissions by up to 50 percent. And 70 percent of all accidents at intersecting roadways are caused by drivers turning left.

According to Layton, some concepts developed in recent years have been touted as a panacea to arterial congestion, such as the two-way left turn lanes located as the "center" lane in a five-lane road. And those ideas can work, he said, up to a point.

"Research has found that two-way left turn lanes are effective only up to a certain level of traffic volume," Layton said. "After that there aren't enough gaps in oncoming traffic to use them safely. And people start to use gaps that are too short, an illegal and dangerous maneuver, as a way of getting onto a crowded road."

The approaches and criteria for access management that OSU researchers have developed and scientifically supported include optimal driveway spacing, appropriate use of medians, appropriate signalized intersection spacing, left and right turn lane standards and management of interchange areas. These are already being implemented around the state by the Oregon Department of Transportation and attracting interest from other states, he said.

"There's concern from business owners that controls on access are a threat to business," Layton said. "But in reality effective access management can set the stage for successful businesses, because people will more often use streets that allow them to get safely, quickly and economically get where they want to go. And conversely, they avoid locations with overly-congested roads or intersections."

The Portland conference next week is the fourth annual conference on access management, Layton said, attracting traffic experts from all over the nation who increasingly realize that dysfunctional arterials are a key problem in our congested urban traffic crisis.

"Traffic experts have known about this issue for some time, and we've recently made strides in making our analyses and standards even more scientific and rational," Layton said. "Now we have to work with city planners, business owners and the public to make the changes necessary to keep traffic moving. It won't always be easy but it can be done."