What is a Roundabout?

A modern roundabout is an unsignalized, circular intersection engineered to maximize safety and minimize traffic delay. Over the last few decades, tens of thousands of roundabouts have been installed in Europe, Australia and other parts of the world. Recently they have gained support in the United States, including communities in Iowa.



Roundabouts benefit from good geometry, exhibiting only a fraction of the troublesome crash patterns typical of right-angle intersections. A typical four-legged intersection has 32 vehicle-to-vehicle conflict points and 24 vehicle-to-pedestrian conflict points. By comparison, a four-legged roundabout has only eight vehicle-to-vehicle conflict points and eight vehicle-to-pedestrian conflict points. This is an approximate 70 percent reduction in conflict points. In addition, since all vehicles are traveling in the same direction and at a lower speed in a roundabout, crashes are generally rear end or sideswipe in nature. Left-hand, right-angle (T-bone) and head-on crashes are virtually eliminated by a roundabout. The illustrations at the top of this page show the conflict points of a standard intersection and a typical roundabout. Studies by the Insurance Institute for Highway Safety show that roundabouts provide a:

  • 90 percent reduction in fatal crashes;
  • 76 percent reduction in injury crashes;
  • 30 to 40 percent reduction in pedestrian crashes; and
  • 10 percent reduction in bicycle crashes
The City of Pleasant Hill constructed its first roundabout at the intersection of NE 70th Street and Rising Sun Drive for improved traffic flow, cost savings, and safety gains.

This brochure includes tips on how to drive roundabouts.

The U.S. Department of Transportation created this video to show why modern roundabouts are a good, safe choice for many roadways.