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Published on May 17, 2011
Did you know that more than 20 people are killed and many more are seriously injured in crashes at intersections every day in the United States? Did you know that most of these deaths and injuries are due to right-angle crashes that occur at signalized and stop-controlled intersections? How much time do you spend stopped at a red light waiting for the light to change when there is no traffic on the cross-street? Did you know there is an intersection alternative that is substantially safer than signalized and stop-controlled intersections and much more efficient?
The USDOT's Federal Highway Administration (FHWA) has identified modern roundabout intersections as one of nine proven life-saving roadway safety strategies. Modern roundabouts are not only safer than traditional signalized and stop-controlled intersections, where appropriate and properly designed, roundabouts operate more efficiently, often have lower life cycle costs, and result in increased fuel efficiency.
So what is a roundabout? A roundabout is a circular intersection. Traffic flows counter-clockwise around a center island. Entering traffic yields to circulating traffic in the roundabout. Channelized approaches using splitter islands deflect traffic as it enters the intersection, slowing speeds. While the vast majority of roundabouts are single lane, one-quarter of the roundabouts in the U.S. have two lanes, which also provide safety benefits. Roundabouts with up to three lanes have been successfully built. Mini-roundabouts can be used in low-speed urban environments in lieu of a stop sign or traffic signal.
Roundabouts are different from other types of circular intersections that you might have seen. They are not rotaries or the older traffic circles, which are still common in the northeastern United States, which typically have higher speeds on approaches and usually higher speeds within the circle. They may use stop- or signal-control, or they may require circulating traffic to yield to entering traffic. A roundabout is also not the same thing as a neighborhood traffic circle, typically used on local streets for speed control.
Roundabouts have several distinguishing characteristics and benefits, setting them apart from other intersection types. Traffic can move freely through roundabouts. This makes them more efficient than signalized or stop-controlled intersections. Unlike other types of intersections, roundabouts are designed to slow the speed of vehicles entering by deflecting them from a straight-line path into the roundabout. Drivers approaching the roundabout have time to judge for gaps in the circulating traffic and either yield or adjust their speed before entering the intersection. This allows for safer entries into circulating traffic.