Roundabouts are relatively new to U.S. roadways

Published 11:46 pm Saturday, May 3, 2008

Roundabouts have been used to control traffic in the United Kingdom since the advent of the automobile. In North America, however, they’ve been scarce until recently.

Large traffic circles, similar to roundabouts, sprang up around America in the 1920s, according to Brian Walsh, a traffic design and operations engineer for the state Department of Transportation.

The old traffic circles didn’t work well and the nation turned to stoplights to handle the burgeoning auto traffic after World War II, he said.

Like many other aspects of the automobile industry, traffic lights also became an industry unto themselves, Walsh said.

A traffic circle is different from a roundabout in two ways. The traffic circle employs stop signs or no signs rather than yield signs, and the approaches are wide open, resulting in kind of a free-for-all, or at more of a right angle. The fountain circle in downtown Edmonds is a good example, Walsh said. Many smaller traffic circles have been built in residential areas in recent years to get drivers to slow down.

In roundabouts, approaches are veered about 30 degrees to the right — or left in the United Kingdom — to move traffic through more smoothly. Lanes leading into roundabouts are more narrow than some traffic circles. Newer roundabouts have small islands outside the circle, separating the directions and providing a stopover for pedestrians.

In the 1980s, research began to show benefits of roundabouts in safety and traffic flow, according to Walsh. In the 1990s, traffic engineers in the United States started catching on, he said.

Most of the nation’s roundabouts have been built since then.

The six roundabouts built in Snohomish County were all built in updated style, with crosswalks just outside the circle, yield signs, angled approaches and a “truck apron,” a sloping curb around the circle that trucks can drive over if necessary. Some have sculptures or landscaping inside the circle.

There are many sizes, shapes and types of roundabouts and traffic circles. Two traffic circles in downtown Arlington, on Division Street at N. West Avenue and N. Broadway Street, use yield signs and function similarly to roundabouts, but have broader approach areas than traditional roundabouts.

“They’re kind of a hybrid,” Arlington public works director Len Olive said.

Reporter Bill Sheets: 425-339-3439 or sheets@heraldnet.com.