Arizona is the latest state to try roundabouts, a type of interchange used in Britain, Europe, and elsewhere, as a cost-effective way to ease traffic congestion.
Roundabouts are designed to move heavy traffic at intersections without stoplights or stop signs. Motorists entering the circular roundabout intersection must yield to vehicles heading counterclockwise. Experts say the waits are minimal as entering vehicles look for a gap in the traffic.
The first Arizona roundabout is planned for what is now a two-lane bridge over Interstate 17, where rapid growth in the Black Canyon corridor is expected to result in more traffic than the current bridge can handle. Building a wider bridge with the traditional freeway access would cost about $12 million.
Instead, roundabouts – large circles – will be built on each side of the highway. Construction is expected to start in the middle of 2000 and should be finished by the end of the year.
State planners are also considering using roundabouts to ease congestion at I-17 and the Carefree Highway.
Arizona's project is not the first U.S. use of roundabouts. Colorado's Rocky Mountain towns of Vail and Avon built high-capacity roundabouts at nine intersections that had caused long delays. Six roundabouts replaced Interstate 70 ramp intersections formerly regulated by stop signs, and three roundabouts replaced intersections with traffic signals in downtown Avon.
Roundabouts have also been tried in Las Vegas, Maryland, Vermont, and Long Beach, CA. Officials in these areas report less wait time and fewer accidents at these intersections.
If you're interested in learning more about roundabouts, visit http://www.roundabouts.com, http://www.roundabout-interchange.com, or http://roundabouts.kittelson.com/.