traffic circle

Columbus Circle, New York City, NY

DeSoto Fountain sits in the center of a traffic circle in the City of Coral Gables, Florida.

Signage for a traffic circle or rotary in New Jersey

A traffic circle is one of several types of circular intersections. Traffic is normally allowed to go in one direction only around a central island. In the absence of signs or signal control, traffic entering a circle has the right-of-way, although many circles give right-of-way to the primary roads or to circulating traffic. In roundabouts^[1] and rotaries^[2] entering traffic must yield to traffic already in the circulatory roadway, though this is not always true of traffic circles.

Characteristics of Traffic Circles

While more precise definitions exist for roundabouts and rotaries, the term "traffic circle" is generally used by engineers to describe circular intersections that lack the defining characteristics of roundabouts or rotaries. Therefore, traffic circles generally have one or more of the following features that roundabouts and rotaries would not:^{[citation needed]}

• Right-angle intersections between approach roadways and the circulatory roadway, or tangential approaches that allow full-speed entry (no flared entry).
• Circulating traffic yields to entering traffic at one or more approach points.
• Exits allowed only from the outer lane of the circular roadway.
• Lane choice on approach is not necessary, lane changes may be made within circle road.
• Pedestrians or other accessible land uses allowed within the center of the circle.

History

French architect Eugène Hénard was designing one-way circular intersections as early as 1877^[3]. American architect William Phelps Eno favored small traffic circles. He designed New York City's famous Columbus Circle, which was built in 1905. Other circular intersections were subsequently built in the United States, though many were large diameter 'rotaries' that enabled high speed merge and weave maneuvers. These designs were doomed to failure for two primary reasons:

• It takes a large diameter circle to provide enough room for merging at speed. Although some of these circles were huge (many were in excess of 100 meters or 300 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 which could not clear without police intervention.

The experience with traffic circles and rotaries in the US was almost entirely negative, characterized by high accident rates and congestion problems. By the mid 1950s, construction of traffic circles and rotaries 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. However, it is not a true traffic circle, as the circular road in question does not form a full circle.

Examples of Traffic Circles

• Monument Circle in downtown Indianapolis, Indiana
• Lee Circle in New Orleans, Louisiana
• Columbus Circle in New York City
• Dupont Circle in Washington, DC
• Place Charles de Gaulle around the Arc de Triomphe in Paris
• Quezon Memorial Circle, Elliptical Road, Quezon City, Metro Manila (Philippines)

Pop culture

Traffic circles are currently featured in the 2009 Mathematical Contest in Modeling. The problem is to determine an optimal design for a traffic circle in terms of traffic flow. This includes technical reports to engineers interested in implementing the models.^[4]

Sources

See also

• List of traffic circles in New Jersey
• List of Circles in Washington, D.C.
• Roundabout
• Rotary (Intersection)