Roundabouts

A modern roundabout is built with a large, circular, raised island located at the intersection of an arterial street with one or more crossing roadways and may take the place of a traffic signal. As with a traffic mini-circle, traffic maneuvers around the circle in a counter clockwise direction, and then turns right onto the desired street. All traffic yields to motorists in the circle and left-turning movements are eliminated. Unlike a signalized intersection, vehicles generally flow and merge through the roundabout from each approaching street without having to stop. Splitter islands at the approaches slow vehicles and allow pedestrians to cross one lane at a time.

The roundabout needs to be constructed to accommodate the needs of pedestrians and bicyclists. Pedestrians may need to travel out of their way to cross the intersection, but generally have a shorter wait than with a signal and have only one direction of approaching traffic to watch for. Unfortunately, visually impaired people have difficulty crossing at roundabouts. This issue needs to be adequately addressed in the design of roundabouts.


Bicyclists usually suffer the most from roundabout design. Unless the road is very narrow (one lane in each direction), speeds very slow, and traffic very light, bicyclists may not be able to share the road comfortably. Marking bicycle lanes through the roundabout has not always been shown to be safer. In larger roundabouts, an off-road bicycle path should be created to direct cyclists to follow the pedestrian route; while this is usually inconvenient and takes longer, it is generally safer.