Traffic circle
A traffic circle or rotary is a type of intersection that has a generally circular central island. Entering traffic must typically alter direction and speed to avoid the island, creating a circular flow in one direction. In most applications, traffic circles replace the stop lights and traffic signs that regulate flow in other intersections.
In English-speaking countries other than the United States, traffic circles are called roundabouts. U.S. traffic engineers use "roundabout" for intersections in which entering traffic must yield to traffic already in the circle, reserving "traffic circle" for those in which entering traffic is controlled by stop signs, traffic signals, or is not formally controlled.[1]
Design
Design criteria include:
- Right-of-way—whether entering or circling vehicles have the right of way. The New Jersey Driver's Manual recommends that circulating traffic yield to entering traffic[2] although there are no set rules. [3]. In New England[4], Washington, D.C. and New York State[5], entering traffic yields, as is the norm in virtually all countries outside of the U.S.
- Angle of entry— Angles range from glancing (tangential) that allow full-speed entry to 90 degree angles (perpendicular).[6]
- Traffic speed—High entry speeds (over 30 mph / 50 km/h) require circulating vehicles to yield, often stopping, which lowers capacity and increases crash rates than modern roundabouts.[7]
- Lane changes— Allowed or not
- Diameter—The greater the traffic, the larger the circle.[6]
- Island function—Parking, parks, fountains, etc.[6]
History
French architect Eugène Hénard was designing one-way circular intersections as early as 1877.[8] 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.
Examples of traffic circles
United States
Massachusetts
- Airport Rotary, Iyannough Road at Barnstable Road in Hyannis, Massachusetts on Cape Cod
- U.S. Route 6 at Massachusetts Route 6A in Orleans, Massachusetts on Cape Cod
- Massachusetts Route 2 & Pearson Boulevard, Gardner, Massachusetts, is a rotary interchange.
- Massachusetts Route 3 & Union Street, Braintree, Massachusetts, is an oval shaped rotary interchange.
- U.S. Route 3 & Massachusetts Route 2, Cambridge, Massachusetts, in a rotary interchange built in a small space.
- Roosevelt Circle (Interstate 93, Route 28 & S Border Road), Medford, Massachusetts, is an oval shaped rotary interchange.
- Interstate 95 & U.S. Route 20, Waltham, Massachusetts, is a large rotary interchange with the on ramps inside the rotary.
- Interstate 95 (wrong-way concurrency with US Route 1) & Canton Street, East Street and Allied Drive in Westwood, Massachusetts is a rotary of surface streets with ramps leading to and from the highway below.
- Mass Route 147 and US Route 5 (as a highway) in West Springfield, Massachusetts is an open circle rotary with access ramps leading to and from the highway below.
- US Route 20 and US Route 5 (as a highway) in West Springfield, Massachusetts is a tunnel style rotary with a mini park in the center where the highway passes through the tunnel. Access ramps leading to and from the highway are provided.
- Massachusetts Route 16 and Massachusetts Route 135 in Wellesley, Massachusetts is the only one in the state where drivers inside the rotary must yield to those entering.
- US Route 5, State Route 57 (Massachusetts), and River Road in Agawam, Massachusetts is a rotary of River Road and Route 57 with US Route 5 (as a highway) as an overpass with access ramps to and from Route 57. It is notorious for near misses due to the awkward ramp configuration.
- Cape Cod Rail Trail rotary in Harwich, Massachusetts
- Exit 5 off Massachusetts Route 6 on Massachusetts Route 149 in Marstons Mills, Cape Cod.
- Grant Circle (Route 128 and Route 127) in Gloucester, Massachusetts dangerous rotary as it interrupts Route 128 just after the A. Piatt Andrew Bridge where it is not uncommon to see people driving at highway speeds not yield to traffic on the rotary despite various warnings.
- Blackburn Circle (Route 128, School House Rd. and Dory Rd.) in Gloucester, Massachusetts large rotary where most of the traffic is continuing traffic along Route 128
Other States
- Monument Circle, surrounding the Soldiers' and Sailors' Monument in downtown Indianapolis, Indiana
- Lee Circle in New Orleans, Louisiana
- Columbus Circle in New York City
- Dupont Circle in Washington, D.C.
- MacArthur Drive Traffic Circle in Alexandria, Louisiana
- U.S. Bypass Highway 1 at U.S. Highway 4 in Portsmouth, New Hampshire (Referred to locally as the Portsmouth Traffic Circle)
- Weatherford Circle, U.S. Highway 377 at Texas State Highway 183 in Benbrook, Texas (Referred to locally as a Traffic Circle)
- Shirlington Circle (Interstate 395 & Virginia State Route 402), Shirlington, Virginia, has off ramps inside the rotary and multiple at-grade streets.
- Union Square (aka "the Oval"), Milford, New Hampshire
- Benjamin Franklin Parkway in Philadelphia
- Bear Mountain Circle in Highland Falls, Orange County, New York, one of a dozen or more in NYS.
Elsewhere
- Place Charles de Gaulle around the Arc de Triomphe in Paris
- Quezon Memorial Circle, Elliptical Road, Quezon City, Metro Manila (Philippines)
- Staples Corner (A406 & M1), Dollis Hill, Greater London, has a freeway ending at a rotary interchange.
- Dammam coastal road, Al-Khalij Street, in Saudi Arabia with a circumference of approximately 1.9 km (1.2 mi)
- Tsuen Kam Interchange, Tsuen Wan, New Territories, Hong Kong
- Glorieta de Bilbao, Madrid, Spain
- El Ángel de la Independencia, in the middle of a large traffic circle ( glorieta ) on the Paseo de la Reforma, Mexico City
Sources
- ^ U.S. Department of Transportation: Roundabouts: an Informational Guide para 1.5
- ^ http://www.state.nj.us/mvc/manuals/chap_04_06.html
- ^ http://www.state.nj.us/mvc/pdf/Licenses/Driver%20Manual/Chapter_4.pdf
- ^ Commonwealth of Massachusetts, Registry of Motor Vehicles. "Sharing the Road: A User's Manual for Public Ways". http://www.mass.gov/rmv/dmanual/index.htm. Retrieved 2009-05-13.
- ^ :http://www.safeny.com/rowa-vt.htm#1145
- ^ a b c Modern Roundabouts, an Informational Guide
- ^ Shashi S. Nambisan, Venu Parimi (March 2007). "A Comparative Evaluation of the Safety Performance of Roundabouts and Traditional Intersection Controls". Institute of Transportation Engineers. http://findarticles.com/p/articles/mi_qa3734/is_200703/ai_n18755716/pg_1. Retrieved 2007-11-27.
- ^ 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
See also