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Columbus Circle, New York City, NY; site of the first traffic circle in the United States completed in 1905

DeSoto Fountain sits in the center of a traffic circle in the city of Coral Gables, Florida.
Photo: Marc Averette

This traffic circle in front of the county courthouse in Angola, Indiana, would be considered a roundabout in the UK. It merely requires entering traffic in all four directions to yield. The island is blocked to traffic or parking by a war memorial. Parking is allowed on the outskirts in place of a weaving area.

Signage for a traffic circle in New Jersey

A traffic circle is an intersection with a circular shape and, usually, a central island. In some traffic circles two-way traffic is allowed within the circle. It is much more common, however, that traffic is allowed to go in one direction only around a central island. In some traffic circles, entering roads are controlled by stop signs or traffic signals. In other cases, traffic enters the circulatory roadway by merging, sometimes at relatively high speeds. Traditionally, traffic entering a circle has the right-of-way, although some circles give right-of-way to the primary roads. In roundabouts, as opposed to traffic circles, entering traffic must yield to traffic already in the circulatory roadway.

French architect Eugène Hénard was designing one-way circular intersections as early as 1877^[1]. American architect William Phelps Eno favored small traffic circles. He designed New York City's famous Columbus Circle, which was built in 1905. Other traffic circles were subsequently built in the United States. Many were large diameter 'rotaries' that enabled high speed merge and weave, and gave priority to the traffic entering the circle. These designs were doomed to failure for two primary reasons:

• It takes a large diameter circle to provide enough room for merging at speed. Despite the fact that some of these circles were huge (many were in excess of 100 meters or 328 feet in diameter), they weren't large enough for high-speed merging.
• Giving priority to entering traffic means that more vehicles can enter the circulatory roadway than it can handle. The result is congestion within the circle.

The experience with traffic circles in the US was almost entirely negative, characterized by high accident rates and congestion problems. By the mid 1950s, construction of traffic circles had ceased entirely. The experience with traffic circles in other countries was not much better until the development of the modern roundabout in the United Kingdom during the 1960s.

Among the most famous traffic circles in the world is that of Canberra, Australia, where a large traffic circle encircles Parliament House. This circle has traffic lights at each major intersection within the circle.

Traffic circles are often composed of concrete or asphalt although more recently rubber curbing is being used to create traffic circles as well, primarily in residential areas. Rubber curbing consists of units of flexible rubber that are bent and installed around a landscaped area to create traffic circles.

1. ^ P. M. Wolf, Eugene Henard and the Beginning of Urbanism in Paris, 1900–1914, International Federation for Housing and Planning, The Hague, 1969, cited by Ben Hamilton-Baillie & Phil Jones, Improving traffic behaviour and safety through urban design, Proceedings of ICE - Civil Engineering, volume 158 Issue 5 May 2005 p. 41 http://www.hamilton-baillie.co.uk/papers/ICE_paper_April05.pdf

• List of traffic circles in New Jersey
• List of Circles in Washington, D.C.