Roundabout Capacity

Roundabouts can be categorized as follows:

• Low-capacity roundabouts have one-lane entries.

• Medium-capacity roundabouts have at least one two-lane entry.

• High-capacity roundabouts have at least one three-lane or four-lane entry.

Ourston Roundabout Engineering, Inc., has designed eight of the nine high-capacity roundabouts in North America. We have designed them in Long Beach, California (1), Las Vegas, Nevada (3), Vail, Colorado (1), Avon, Colorado (2), and Addison, Texas (1). Leif Ourston personally designed the first five high-capacity roundabouts ever built in the United States.

The roundabouts are presented by year of construction in the following table. The number of lanes on the widest entry is given for each roundabout.

North America's Nine High-Capacity Roundabouts

The United Kingdom has hundreds of high-capacity roundabouts. In North America, since we have many more high-flow intersections than the United Kingdom, we need many more high-capacity roundabouts.

Our worst concentrations of traffic crashes tend to be at signalized intersections. Many of these need to be replaced by roundabouts, which may cause about half as many crashes as signalized cross intersections carrying similar flows. See Safety for more on this topic.

Most importantly, we need to replace many high-speed, often rural, signalized intersections with roundabouts. Because a roundabout slows all traffic, in the United Kingdom it is the intersection of choice where high-speed highways cross. Traffic signals that regulate high-speed crossings tend to cause too many angle and rear-end crashes, often with serious injuries. The most important high-speed crossings to convert to roundabouts are those carrying high flows. At these sites we urgently need high-capacity roundabouts.

In North America our sites of worst delay and longest queues are often high-flow signalized intersections. We have many signalized intersections from which traffic backs up during peak periods as far as the eye can see. High-capacity roundabouts ordinarily eliminate long queues when they replace traffic signals.

We welcome the opportunity to help you design high-capacity roundabouts to replace problem intersections on your road system. High-capacity roundabouts are North America's most needed type of intersection.