Editing Roundabout (section)

{{Short description|Traffic intersection}}
{{About|the road junction||Roundabout (disambiguation)|and|Rotary (disambiguation)}}
{{redirect|Traffic circle|the glaciated area in Antarctica|Traffic Circle (Antarctica)}}
{{Use dmy dates|date=May 2025}}
{{Use British English|date=January 2017}}

[[File:Roundabout 14 61.webm|thumb|300px|Roundabout in [[La Crosse, Wisconsin]]]]
{{multiple image
| align             = right
| image1            = NonUK Roundabout 8 Cars.gif
| width1            = 200
| alt1              = Sparta Army National Guard
| caption1          = Movement within a roundabout in [[right- and left-hand traffic|right-hand traffic]]; note the [[clockwise|anticlockwise]] circulation
| image2            = UK Roundabout 8 Cars.gif
| width2            = 200
| alt2              = UK Roundabout
| caption2          = Movement within a roundabout in [[Right- and left-hand traffic|left-hand traffic]]; note the [[clockwise]] circulation
}}
[[File:Jakarta Bundaran HI .jpg|thumb|[[Bundaran HI|The Hotel Indonesia Roundabout]] in [[Jakarta, Indonesia]]]]
[[File:Magic Roundabout in Hemel Hempstead.JPG|thumb|A ring junction in [[Hemel Hempstead]], UK]]
A '''roundabout''', a '''rotary''' and a '''traffic circle''' are types of circular [[intersection (road)|intersection]] or junction in which road [[traffic]] is permitted to flow in one direction around a central island, and priority is typically given to traffic already in the junction.<ref name="oxford">''The New Shorter Oxford English Dictionary,'' Volume 2, Clarendon Press, Oxford (1993), page 2632</ref>{{sfn|U.S. Department of Transportation|2013|loc=para 1.5}}

In the United States, engineers use the term '''modern roundabout''' to refer to junctions installed after 1960 that incorporate design rules to increase safety.<ref name="Ourston1995"/>{{sfn|U.S. Department of Transportation |2013 |loc=para 1.5}} Compared to stop signs, traffic signals, and earlier forms of roundabouts, modern roundabouts reduce the likelihood and severity of collisions greatly by [[Traffic calming#Engineering measures|reducing traffic speeds]] through horizontal deflection and minimising [[Side collision#Broadside or T-bone collision|T-bone]] and [[head-on collisions]].<ref>{{cite web |title=Module 3: Toolbox of Individual Traffic Calming Measures Part 2 {{!}} FHWA |url=https://highways.dot.gov/safety/speed-management/traffic-calming-eprimer/module-3-part-2#3.9 |website=highways.dot.gov |access-date=4 May 2025 |language=en}}</ref><ref>{{cite web |title=Roundabout Benefits |url=http://www.wsdot.wa.gov/safety/roundabouts/benefits.htm |website=Washington State Department of Transportation |access-date=12 July 2014}}</ref> Variations on the basic concept include integration with tram or train lines, two-way flow, higher speeds and many others.

For pedestrians, traffic exiting the roundabout comes from one direction, instead of three, simplifying the pedestrian's visual environment. Traffic moves slowly enough to allow visual engagement with pedestrians, encouraging deference towards them. Other benefits include reduced driver confusion associated with perpendicular junctions{{citation needed|date=August 2024}} and reduced queuing associated with [[traffic light]]s. They allow [[U-turns]] within the normal flow of traffic, which often are not possible at other forms of junction. Moreover, since vehicles that run on petrol or diesel typically spend less time idling at roundabouts than at signalled intersections, using a roundabout potentially leads to less pollution.<ref>{{cite web |last=Hesch |first=Maxine |title=Quantitatively Determining the Emissions Reduction Benefits of the Replacement of a Signalized Intersection by a Roundabout |url=https://www.dot.ny.gov/main/roundabouts/files/Emissions_Reduction.pdf |publisher=New York State Department of Transportation |access-date=6 October 2013}}</ref><ref name=iihs/> When entering vehicles only need to give way, they do not always perform a full stop; as a result, by keeping a part of their momentum, the engine will require less [[Work (physics)|work]] to regain the initial speed, resulting in lower emissions. Research has also shown that slow-moving traffic in roundabouts makes less noise than traffic that must stop and start, speed up and brake.<ref>{{cite web |url=http://www.tc.gc.ca/eng/motorvehiclesafety/tp-tp14787-menu-179.htm |title=Roundabout Rules of the Road |access-date=12 January 2014 |url-status=dead |archive-url=https://web.archive.org/web/20140109034043/http://www.tc.gc.ca/eng/motorvehiclesafety/tp-tp14787-menu-179.htm |archive-date=9 January 2014}}</ref>

Modern roundabouts were first standardised in the UK in 1966 and were found to be a significant improvement over previous traffic circles and rotaries. Since then, modern roundabouts have become commonplace throughout the world,{{sfn|U.S. Department of Transportation|2013|loc=para 1.5}}{{rp|2}} including Australia, the United Kingdom and France.<ref name="iihs">{{Cite web |url=https://www.iihs.org/topics/roundabouts |title=Roundabouts |website=IIHS-HLDI crash testing and highway safety}}</ref>

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