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A traffic circle is a type of intersection that directs both turning and through traffic onto a one-way circular roadway, usually built for the purposes of traffic calming or aesthetics.〔(Victoria Transportation Policy Institute Online TDM Encyclopedia: Traffic Calming (modern roundabouts section) )〕 Contrary to a roundabout, where entering traffic always yields to traffic already in the circle and merges in directly, the entrances to traffic circles are 3-way intersections either controlled by stop signs, traffic signals, or not formally controlled.〔(U.S. Department of Transportation: ''Roundabouts: an Informational Guide'' para 1.5 )〕 Colloquially, however, roundabouts are sometimes referred to as circles. In the United States, traffic engineers typically use the term rotary for large scale circular junctions between expressways or controlled-access highways. Rotaries typically feature high speeds inside the circle and on the approaches.〔(U.S. Department of Transportation: Safety Aspects of Roundabouts presentation )〕 In New England, roundabouts are generally called rotaries and the traffic that is already driving in the rotary always has the right of way. For examples of where this is specified, in Massachusetts "Any operator of a vehicle entering a rotary intersection shall yield the right-of-way to any vehicle already in the intersection.".〔()〕 In Rhode Island entering vehicles "Yield to vehicles in the roundabout." 〔()〕 Distinct from roundabouts, traffic circles and rotaries may also have an interior lane that requires traffic on it to change lanes in order to exit the circle.〔(U.S. Department of Transportation: ''Technical Summary: Roundabouts'' )〕 ==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, in the absence of flow control signs, traffic yields based on "historically established traffic flow patterns",〔http://www.state.nj.us/mvc/manuals/chap_04_06.html〕 and there are no set rules.〔http://www.state.nj.us/mvc/pdf/Licenses/Driver%20Manual/Chapter_4.pdf〕 In New England,〔(【引用サイトリンク】title=Sharing the Road: A User's Manual for Public Ways )〕 Washington, D.C. and New York State,〔:http://www.safeny.com/rowa-vt.htm#1145〕 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).〔(''Roundabout: an Informational Guide'' )〕 * 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 compared to modern roundabouts. * Lane changes— Allowed or not * Diameter—The greater the traffic, the larger the circle.〔 * Island function—Parking, parks, fountains, etc.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Traffic circle」の詳細全文を読む スポンサード リンク
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