Traffic circle
From Wikipedia, the free encyclopedia
A traffic circle is an intersection with a circular shape and, usually, a central island. Traffic is allowed to go in one direction only around a central island. Traditionally, traffic entering a circle has the right-of-way, although some circles give right-of-way to the primary roads. In roundabouts and often rotaries, as opposed to traffic circles,[citation needed] entering traffic must yield to traffic already in the circulatory roadway.
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[edit] History
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. 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.
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 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.
The largest traffic circle in the world is claimed to be one of those in the Dammam coastal road, Al-Khalij Street, in Saudi Arabia with a length of approximately 1.9 km (1.20 miles) [2]
[edit] Composition
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.
[edit] Examples of Traffic Circles
- Monument Circle in downtown Indianapolis, Indiana
- Columbus Circle in New York City
- DuPont Circle in Washington, DC
- Place de l'Etoile around the Arc de Triomphe in Paris
[edit] 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. [3]
[edit] Sources
- ^ 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
- ^ [1] wikimapia.org
- ^ 2009 Mathematical Contest in Modeling: Problems
[edit] See also
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