Roundabouts cut traffic accidents, experts say

The city of Spokane Valley recently finished construction on its third roundabout this year, making it a leader among local jurisdictions using the giant rings of concrete to send drivers curving through an intersection.

The premise is simple. When drivers approach a roundabout, they slow to about 20 miles per hour and enter the circle by turning to the right. They continue around the circle until they reach the direction they want to go, then turn out of the circle. Approaching drivers must yield to cars already in the roundabout, which have the right-of-way.

A roundabout can handle more traffic than a four-way stop, said Spokane Valley traffic engineer Inga Note. Most accidents at intersections are T-bone accidents, which have the potential for serious injury. Installing a roundabout virtually eliminates that type of accident. “They have better safety records,” Note said of roundabouts. “That’s the reason traffic engineers like them so much.”

Spokane Valley just finished a roundabout at Mission Avenue and Flora Road this summer. One was built last year at Broadway Avenue and Flora. The first to be built in Spokane Valley was at Wilbur Road and Mansfield Avenue in late 2008.

The very first roundabout in the region was put in by the city of Spokane at Wellesley Avenue and “A” Street in the summer of 2005. Before the roundabout was installed, numerous community meetings were held and residents vilified the city for wanting to install such a newfangled thing. “People thought we were Satan, of course,” said Spokane traffic operations engineer Bob Turner, who attended the meetings.

But people quickly warmed to the roundabout once it went in. “Within a year or two we had people requesting that we put in more,” he said.

Even better, accidents at the intersection dropped dramatically. In 2004 there were nine accidents at the intersection, Turner said, and all were T-bone accidents. In 2006 there was not a single accident. “It made a real big difference,” he said.

Spokane now has a roundabout at Lincoln Street and Crestline Avenue, plus two traffic calming circles near Gonzaga University and in Browne’s Addition. The traffic calming circles are nearly identical to roundabouts, just a little smaller. “There are subtle differences,” said Spokane operations engineer Andy Shank.

The Washington State Department of Transportation also maintains a roundabout at Bruce Road and Mount Spokane Park Drive.

A roundabout wouldn’t work on a major intersection like Sprague Avenue and Sullivan Road, but they are useful for minor arterials, said Note. They are cheaper to maintain than traffic signals and have “refuge islands” where pedestrians can pause in between lanes of traffic, she said. “I think they’re safer than standard stop-controlled intersections,” Note said. “When they cross they only have to deal with one direction of traffic at a time.”

Though the current number of roundabouts is small, it’s obvious that the numbers are slowly growing and more are to come. They are part of every engineer’s “tool box,” said Turner. “Now that’s part of the discussion every time we look at a problem intersection.”