How Roundabouts Work

http://www.iihs.org/video.aspx/info/roundabout (This roundabout video is hosted on the Insurance Institute for Highway Safety website. For additional topics, view their video index.)

A modern roundabout is a circular intersection where traffic flows around a center island. Roundabouts are not traffic circles or the older-style rotary traffic islands found in some East Coast and European cities. Roundabouts have proven themselves to be safe and efficient. Since vehicles entering the roundabout are required to yield to traffic in the circle, more vehicles can move through the intersection with less delay. The unique one-way design of roundabouts also accommodates the turning radius of large vehicles, like semi-trucks and buses. 
 
Communities are turning to this traffic control device as a means to manage traffic by reducing conflicts and increasing intersection capacity, controlling speed and, most importantly, reducing crashes at intersections. Research has shown that roundabouts are considerably safer than typical intersections.  A study done by the Insurance Institute for Highway Safety found that where roundabouts have been installed, motor vehicle crashes have declined by about 40 percent, and injury crashes have been reduced by approximately 80 percent!  This significant reduction in accidents is largely due to the lower number of conflict points. Conflict points are those areas where collisions could occur as traffic paths cross. At a traditional four-way intersection there are 32 potential conflict points.  In a roundabout that number is reduced to eight, and those serious right angle crashes are virtually eliminated.
 
Modern roundabouts are being constructed more and more in the state of Washington, in the United States, and around the world.  They are being built in a wide range of environments: urban and rural settings, as part of large developments, in new residential subdivisions, next to big box retail, near fire stations, police stations, schools, and convention centers, at airports and national parks, and in areas where snow and ice frequently occur. At last count, there were approximately 110 roundabouts in the State of Washington and 1,000 roundabouts in North America!
 
If you are looking for improved safety for drivers, pedestrians and bicyclists, and improved traffic flow with reduction in vehicle emissions and fuel consumption, then you should take a closer look at the modern roundabout.  I think you will like what you see.
 
Jeff Palmer
Neighborhood Traffic Calming Coordinator
City of Redmond
Public Works/Transportation Services