Editing Roundabout

{{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>

{{toclimit|3}}

==History==

=== Origins and demise of traffic circles ===
Circular junctions existed before roundabouts, including:
* 1768 [[United Kingdom]]: The [[Circus (Bath)|Circus]] in the city of [[Bath, Somerset]] was completed. This was constructed based on architectural considerations and not for traffic purposes.
* 1780 (ca.) [[France]]: The [[Place de l'Étoile]] around the [[Arc de Triomphe]] in Paris.
* 1791 [[US]]: [[Pierre Charles L'Enfant]] (who came to America in 1776) designed a [[L'Enfant_Plan|plan of Washington, D.C.]], which was then being planned. This design contained several large places/street crossings. Many of them had a rectangular outer outline, but within each was a place, around which the streets should be built, thus reducing the number of arms/legs of each crossing.
* 1821 US: The Governor's Circle (later renamed [[Soldiers' and Sailors' Monument (Indianapolis)#Monument Circle|Monument Circle]]) of [[Indianapolis]], Indiana (which gave the city the nickname "The Circle City");
* 1877 France: The French architect [[Eugène Hénard]] was designing one-way circular intersections.<ref>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 and Phil Jones, ''Improving traffic behaviour and safety through urban design'', Proceedings of ICE – Civil Engineering| volume=158 Issue 5 May 2005 p. 41 {{cite web|url=http://www.hamilton-baillie.co.uk/papers/ICE_paper_April05.pdf |title=Archived copy |access-date=10 October 2006 |url-status=dead |archive-url=https://web.archive.org/web/20070730130826/http://www.hamilton-baillie.co.uk/papers/ICE_paper_April05.pdf |archive-date=30 July 2007 }}</ref>
* 1879 [[Netherlands]]: The Keizer Karelplein in [[Nijmegen]].<ref name="Verhoeven">{{Cite book |last=Verhoeven |first=Dolly (red.) |date=2009 |title=De Canon van Nijmegen |location=Nijmegen |publisher=Uitgeverij Vantilt |page=131 |isbn=9789460040351}}</ref>
* 1899 [[Germany]]: Brautwiesenplatz in [[Görlitz]].<ref>{{Cite web|url=http://www.alles-lausitz.de/was-alles-in-goerlitz-erfunden-wurde.html|title=Was alles in Görlitz erfunden wurde – Alles-Lausitz.de|website=Alles-Lausitz.de|language=de|access-date=5 June 2017|archive-url=https://web.archive.org/web/20170807120730/http://www.alles-lausitz.de/was-alles-in-goerlitz-erfunden-wurde.html|archive-date=7 August 2017|url-status=dead}}</ref>
* 1904 US: [[Columbus Circle]] in [[Manhattan]], New York.
* 1905 US: American architect [[William Phelps Eno]] favoured small traffic circles.<br>He re-designed New York City's famous Columbus Circle, which was finished in 1905.
* 1907 US: Architect John McLaren designed one of the first American traffic circles for both autos and streetcars (trams) in the [[Shasta/Hanchett Park, San Jose, California|Hanchett Residence Park]] in what is now [[San Jose, California]].<ref>http://twofeet.weebly.com/walking-blog/the-five-circles-of-hanchett-park The Five Circles of Hanchett Park, 7 June 2014</ref>
* 1909 United Kingdom: The first British circular junction was built in [[Letchworth Garden City]].<ref>{{cite news|url=http://news.bbc.co.uk/1/hi/magazine/3972979.stm|author=BBC News|title=Roundabout Magic|access-date=13 May 2007 | date=2 November 2004}}</ref><ref>{{cite web |url=http://www.letchworthgc.com/cgi-bin/news_fullstory.cgi?newsid=72 |author=Letchworth Garden City Heritage Foundation |title=Sign of the Times |access-date=14 December 2006 |archive-url=https://web.archive.org/web/20061016113507/http://www.letchworthgc.com/cgi-bin/news_fullstory.cgi?newsid=72 |archive-date=16 October 2006 |url-status=usurped}}</ref>

Although some may still be referred to as ''roundabouts'', the operating and entry characteristics of these traffic circles differed considerably from modern roundabouts.<ref name="NAP"/>

Circular intersections were built in the United States, though many were large-diameter 'rotaries' that enabled high-speed merge and weave manoeuvres. Older-style traffic circles may control entering traffic by stop signs or traffic lights. Many allow entry at higher speeds without deflection, or require a stop and a 90-degree turn to enter. Because these circumstances caused a lot of vehicle collisions, construction of traffic circles and rotaries ceased in the 1950s, and some were removed.<ref name="Beldon">{{Cite web |url=https://www.youtube.com/watch?v=AqcyRxZJCXc|archive-url=https://ghostarchive.org/varchive/youtube/20211211/AqcyRxZJCXc| archive-date=11 December 2021 |url-status=live|title=Why The U.S. Hates Roundabouts |author=Christine Beldon |work=[[Cheddar (TV channel)|Cheddar]] |date=17 December 2019 |access-date=18 April 2021}}{{cbignore}}</ref>{{rp|at=3:02}}
<gallery widths="200" heights="160" class="center">
File:South-Yarmouth-MA-US rotary plaque.JPG|[[National Register of Historic Places]] plaque on the first traffic circle in the United States, at the intersection of River and Pleasant streets in [[Yarmouth, Massachusetts]]
File:Thomas-Circle Washington-DC 1922.jpg|Thomas Circle in Washington, D.C., 1922
File:Place Charles-de-Gaulle from the Arc de Triomphe, July 2001.jpg|Traffic ten abreast traverses the ''[[Place de l'Étoile]]''. This traffic circle surrounds the ''[[Arc de Triomphe]]'' at the intersection of ten two-way and two one-way streets. It has no lane markings.
</gallery>

=== 1960s development of modern roundabouts ===
[[File:Letchworth Roundabout 1909.jpg|thumb|The United Kingdom's first roundabout (1909) in [[Letchworth Garden City]]]]
Widespread use of the modern roundabout began when the UK's [[Transport Research Laboratory]] engineers re-engineered and standardised circular intersections during the 1960s. [[Frank Blackmore (traffic engineer)|Frank Blackmore]] led the development of the "priority rule" and subsequently invented the mini-roundabout<ref>{{cite news |title= Frank Blackmore: traffic engineer and inventor of the mini-roundabout |url=http://www.timesonline.co.uk/tol/comment/obituaries/article4131930.ece |archive-url=https://web.archive.org/web/20100524152615/http://www.timesonline.co.uk/tol/comment/obituaries/article4131930.ece |url-status=dead |archive-date=24 May 2010 |work=The Times |date=14 June 2008 |access-date=15 June 2008 | location=London}}</ref><ref name="ourston.com">{{cite news | url=http://www.ourston.com/updates-archive/114.html | title=Leif Ourston receives Frank Blackmore Award | work=[[Ourston.com]] | date=13 January 2010 | access-date=7 October 2013 | author=Ourston Roundabout Engineering, Inc | url-status=dead | archive-url=https://web.archive.org/web/20131029230042/http://www.ourston.com/updates-archive/114.html | archive-date=29 October 2013 | df=dmy-all }}</ref> to overcome capacity and safety limitations. The priority rule was found to improve traffic flow by up to 10%.<ref>Clint Pumphrey. [https://science.howstuffworks.com/engineering/civil/roundabouts1.htm "How Roundabouts Work"]. howstuffworks.com</ref> In 1966, the United Kingdom adopted a rule at all circular junctions that required entering traffic to give way to circulating traffic. A [[Transportation Research Board]] guide reports that the modern roundabout represents a significant improvement, in terms of both operations and safety, when compared with older rotaries and traffic circles.<ref name="NAP">{{Cite book |last=National Academies of Sciences |first=Engineering |url=https://www.nap.edu/catalog/22914/roundabouts-an-informational-guide-second-edition |title=Roundabouts: An Informational Guide |edition=2nd |date=4 December 2010 |doi=10.17226/22914 |isbn=978-0-309-15511-3 |language=en}}</ref> The design became mandatory in the United Kingdom for all new roundabouts in November 1966.<ref>{{Cite web |title=Roundabouts: A Direct Way to Safer Highways {{!}} FHWA |url=https://highways.dot.gov/public-roads/autumn-1995/roundabouts-direct-way-safer-highways |access-date=15 September 2023 |website=highways.dot.gov}}</ref> Australia and other British-influenced countries were the first outside the UK to build modern roundabouts.<ref name="Ourston1995"/>

=== Spread in Europe and North America since 1970s ===
* In 1951, Cyprus, British Crown colony back then, adopted the roundabout in the main cities.
* In the 1970s, [[France]] and [[Norway]] adopted the modern roundabout.<ref name="Kooman"/>
* In 1973, the U.S. city of [[Seattle]] began installing small traffic circles within existing intersections to calm traffic.<ref>{{cite news |last=Hadley |first=Jane |date=22 November 2004 |title=Getting There: Perks for drivers of hybrid cars? Sorry, and here's why not |page=B1 |url=http://seattlepi.nwsource.com/transportation/200597_get22.html |work=[[Seattle Post-Intelligencer]] |url-status=dead |archive-url=https://web.archive.org/web/20041122203835/http://seattlepi.nwsource.com/transportation/200597_get22.html |archive-date=22 November 2004 |accessdate=29 February 2024}}</ref> {{As of|2021}}, the city has installed over 1,200 traffic circles, primarily in residential neighborhoods.<ref>{{cite news |last=Dahl |first=Doug |date=18 January 2021 |title=With a wink and a nod, a quick left often is drivers' go-to move at calming circles |url=https://www.bellinghamherald.com/news/traffic/rules-of-the-road/article248506375.html |work=[[The Bellingham Herald]] |accessdate=29 February 2024}}</ref>
* In 1980, [[Switzerland]] had 19 roundabouts.<ref name="Ourston1995"/>
* In 1980, Norway had 15 roundabouts.<ref name="Ourston1995"/>
*In the early 1980s, single-lane roundabouts (or mini-roundabouts) were also introduced in the [[Netherlands]].<ref name="Kooman"/> It began in the relatively sparsely populated northern and eastern Netherlands because of fears that the roundabouts would not be able to cope with the traffic density of the [[Randstad]]; however, when it appeared the single-lane roundabouts had an even higher capacity than signalised intersections, they were constructed en masse in the western Netherlands as well.<ref name="Kooman"/>
* In 1983, France adopted the yield-at-entry rule on national routes; since then the country's roundabouts have proliferated.<ref name="Ourston1995"/>
* In 1985, Norway put up yield signs at the entries to all its roundabouts. After this, safety and traffic flow rapidly improved,<ref name="Ourston1995"/> and Norwegian roundabouts increased from 15 in 1980, to 350 in 1990, to 500 in 1992.<ref name="Ourston1995"/>
* In 1987, Switzerland introduced the yield-at-entry rule; since then its roundabouts increased from 19 in 1980 to 220 in early 1992, while 500 more were being considered.<ref name="Ourston1995"/>
* In the late 1980s, the Netherlands saw significant growth with about 400 roundabouts constructed in just 6 years.<ref name="Ourston1995"/> Construction accelerated in the 1990s, and by 2001, there were an estimated 1,500 to 1,800 roundabouts in the Netherlands, more than half of which were located within built-up areas.<ref name="Kooman">{{Cite journal |last1=Kooman |first1=Bas |date=March 2001 |url=https://books.google.com/books?id=gJFsyiHOUXIC&pg=PT65 |title=De rotonde. Veilig rondjes rijden? |journal=[[Kampioen]] |volume=116 |issue=3 |pages=65–66 |language=nl}}</ref>
* In 1990, the US constructed its first modern roundabout, although older roundabouts have been somewhat common in parts of the Northeast (called rotaries or traffic circles).
* In 1991, France was building 1,000 roundabouts every year.<ref name="Ourston1995"/>
* As modern roundabouts rose in popularity in the 1980s, the old traffic circles fell out of favour and many were converted into modern roundabouts or other types of intersections.<ref name="Ourston1995"/>
* In 1999, Canada built its first modern roundabout.<ref name="Tollazzi"/>
* As of the beginning of the 21st century, roundabouts were in widespread use in Europe. For instance:
** In 2010, France had more than 30,000 roundabouts.<ref name="Keh 2010">{{cite news |last=Keh |first=Andreh |title=European Import Has Cars Spinning. Heads, Too |url=https://www.nytimes.com/2010/11/19/us/19roundabouts.html |access-date=19 November 2010 |work=[[The New York Times]] |date=18 November 2010 }}</ref>
** There were around 25,000 in the United Kingdom in 2015.<ref>{{cite news | url=https://www.theguardian.com/cities/2015/oct/19/traffic-lights-roundabouts-way-out | title='Traffic lights are so dictatorial' ... but are roundabouts on the way out? | work=[[The Guardian]] | date=19 October 2015 | access-date=13 February 2020 | author=Wylie, Ian}}</ref>

<gallery widths="200" heights="160" class="center">
File:Aangekocht in 1991 van United Photos de Boer bv. - Negatiefnummer 32989 k 6 a. - Gepubliceerd in het Haarlems Dagblad van 15.09.1990.JPG|Roundabout, [[Haarlem]], Netherlands, 1990. Cyclists may also be users of a roundabout.
File:Pacionfi.JPG|Small roundabout in [[Barzio]], Italy
File:Straßwalchen kreisverkehr 2.jpg|Roundabout in [[Straßwalchen]], Austria
File:Colombo Galle Face Roundabout.JPG|Roundabout in the centre of [[Colombo]], Sri Lanka
File:Зеница 20180730 175900.jpg|Double-lane Raindrop Fountain Roundabout in [[Zenica]], Bosnia and Herzegovina, where roundabouts replaced all traffic lights since 2011.
File:Rydsrondellen.JPG|Roundabout signs in [[Linköping]], Sweden
File:British Direction Sign 1.svg|A roundabout sign example used in the UK
</gallery>

=== North American introduction since 1990s ===
{{multiple image
| align             = right
| direction         = horizontal
| image1            = 2020-05-23 11 54 16 View east along Maryland State Route 231 (Prince Frederick Road) from the overpass for Maryland State Route 5 (Leonardtown Road) in Hughesville, Charles County, Maryland.jpg
| width1            = 200
| alt1              = 
| caption1          = Modern roundabout in Hughesville, Maryland in 2020
| image2            = Murrayville 01 roundabout.jpg
| width2            = 211
| alt2              = 
| caption2          = Modern roundabout intersection in Murrayville, Langley, British Columbia
| caption3          = Roundabout sign in Ontario, Canada
| image3            = Ontario Roundabout Sign.png
| width3            = 145
}}

In the United States modern roundabouts emerged in the 1990s after years of planning and educational campaigning by Frank Blackmore and [[Leif Ourston]], who sought to bring the by then well-established increased safety and traffic flow in other countries to America.<ref name="Beldon"/>{{rp|at=5:03}} The first was constructed in [[Summerlin, Nevada]], in 1990 and was followed by another the following year.<ref name="Ourston1995"/><ref name="roundaboutsusa.com">{{Cite news |last=Wright |first=Lucas |date=18 September 2019 |title=Highlighting the first modern roundabouts in the country during National Roundabout Week |url=https://www.8newsnow.com/news/local-news/highlighting-the-first-modern-roundabouts-in-the-country-during-national-roundabout-week/ |publisher=[[KLAS-TV|KLAS]] |accessdate=29 February 2024}}</ref> This roundabout occasioned dismay from residents, and a local news program said about it, "Even police agree, [roundabouts] can be confusing at times."<ref>{{cite news | first=Dayna | last=Roselli | title=Roundabouts | url=http://blogs.lasvegasnow.com/traffic/2007/04/18/roundabouts/8 | publisher=lasvegasnow.com | date=18 April 2007 |archive-url=https://web.archive.org/web/20120326150503/http://blogs.lasvegasnow.com/traffic/2007/04/18/roundabouts/8/ | archive-date=26 March 2012 | access-date=14 October 2014}}</ref> Between 1990 and 1995, numerous modern roundabouts were built in California, Colorado, Florida, Maryland, Nevada, and Vermont.<ref name="Ourston1995"/>
[[File:Holmen round about.jpg|thumb|Roundabout built in 2023 in [[Holmen, Wisconsin]]]]
Municipalities introducing new roundabouts often were met with some degree of public resistance, just as in the United Kingdom in the 1960s.
* American confusion at how to enter and especially how to exit a roundabout was the subject of mockery such as featured in the film ''[[National Lampoon's European Vacation|European Vacation]]'' (1985).<ref name="Keh 2010"/><ref name=BBC2011/><ref name="Beldon"/>{{rp|at=6:45}}
* A 1998 survey of municipalities found public opinion 68% opposed prior to construction, changing thereafter to 73% in favour.<ref>{{Cite web|url=http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_syn_264.pdf|title=Modern Roundabout Practice in the United States}}</ref>
* A 2007 survey found public support ranging from 22% to 44% prior to construction, and several years after construction was 57% to 87%.<ref>{{cite journal |last1=Retting |first1=Richard A. |first2=Sergey Y. |last2=Kyrychenko |first3=Anne T. |last3=McCartt |title=Long-Term Trends in Public Opinion Following Construction of Roundabouts |journal=Journal of the Transportation Research Board |volume=2019 |year=2007 |pages=219–224 |doi=10.3141/2019-26 |s2cid=110914100 }}</ref>
* By 2011, however, some 3,000 roundabouts had been established, with that number growing steadily.<ref name="Keh 2010"/><ref name=BBC2011>{{cite news|url=https://www.bbc.co.uk/news/magazine-13863498 |title=Is the British roundabout conquering the US?|author=Tom Geoghegan |date=1 July 2011 |work=BBC website|access-date=1 July 2011}}</ref><ref name="Beldon"/>{{rp|at=6:45}}

In the mid-2010s, about 3% of the then circa 4,000 U.S. modern roundabouts were located in [[Carmel, Indiana]], whose mayor [[James Brainard]] had been actively promoting their construction; because of increased safety, injuries caused by car accidents in the city dropped by 80% after 1996.<ref name="Beldon"/>{{rp|at=0:02}} {{As of|December 2015}} there were about 4,800 modern roundabouts in the United States.{{citation needed|date=July 2021}} As an example, [[Washington (state)|Washington state]] contained about 120 roundabouts {{as of|October 2016|lc=y}}, all having been built since 1997, with more planned.<ref>{{cite web |url=http://www.wsdot.wa.gov/safety/roundabouts/washingtons.htm |title=WSDOT – Washington's Roundabouts |date=11 October 2016 |archive-url=https://web.archive.org/web/20161011143946/http://www.wsdot.wa.gov/safety/roundabouts/washingtons.htm |archive-date=11 October 2016 |url-status=dead |access-date=17 October 2018}}</ref>

The first Canadian traffic circles were in Edmonton. There were 7 such by 1954. However, they didn't gain popularity in the rest of the country until the 1990s. They became increasingly popular amongst traffic planners and civil engineers in the 15 years thereafter due to their success in Europe. By 2014 there were about 400 roundabouts in Canada at the time (most in Quebec, Alberta, British Columbia and Ontario), or one per 90,000 inhabitants (compared to one per 84,000 inhabitants in the United States that year).<ref name="Tollazzi">{{Cite book |last=Tollazzi |first=Tomaž |date=2014 |title=Alternative Types of Roundabouts: An Informational Guide |url=https://books.google.com/books?id=qf85BQAAQBAJ&pg=PA110 |location=Cham |publisher=Springer |page=110 |isbn=9783319090849 |access-date=18 April 2021}}</ref>

== Modern roundabout ==
{{multiple image
| align             = right
| direction         = horizontal
| header            = Roundabout sign examples
| header_align      = center
| caption_align     = center
| total_width       = 350
| image1            = Vienna Convention road sign D3a.svg
| height1           = 85
| alt1              = 
| caption1          = [[Vienna Convention on Road Signs and Signals|Vienna Convention]] mandatory
| image2            = NO road sign 126.svg
| height2           = 85
| alt2              = 
| caption2          = Vienna Convention warning
| image3            = MUTCD W2-6.svg
| height3           = 85
| alt3              = 
| caption3          = [[MUTCD]] warning
| image4            = SADC road sign R2.2-RHT.svg
| height4           = 85
| alt4              = 
| caption4          = Give Way<br>(Yield)
| footer            = [[Right-hand traffic]] shown. Direction arrows are mirrored for left-hand traffic
| footer_align      = center
}}

A "''modern'' roundabout" is a type of looping [[road junction|junction]] in which road traffic travels in one direction around a central island and priority is given to the circulating flow. Signs usually direct traffic entering the circle to slow and to [[traffic#Passage Priority (right of way)|give way]] to traffic already on it.<ref name="Turner-Fairbank Highway Research Center">
{{cite web
 |url          = http://www.tfhrc.gov/safety/00068.pdf
 |title        = Roundabouts: an informational guide
 |date         = 16 November 2017
|publisher    = Turner-Fairbank Highway Research Center
 |access-date   = 5 December 2017
|url-status      = bot: unknown
 |archive-url   = https://web.archive.org/web/20090112070051/http://www.tfhrc.gov/safety/00068.pdf
 |archive-date  = 12 January 2009
|df           = dmy-all
}}</ref><ref name=AXA_Insurance>
{{cite web
| url         = https://www.axa.ie/articles/entry/what-lane-should-i-use-on-a-roundabout/
| title       = What lane should I use on a roundabout?
| date        = 16 November 2017
| website     = AXA.ie
| publisher   = AXA
| access-date  = 16 November 2017
}}</ref>

Because low speeds are required for traffic entering roundabouts, they are physically designed to slow traffic entering the junction to improve safety, so that the roads typically approach the junction ''radially''; whereas older-style traffic circles may be designed to try to increase speeds, and have roads that enter the circle ''tangentially''.

Roundabouts are normally not used on [[controlled-access highways]] because of the low speed requirement, but may be used on lower grades of highway such as [[limited-access road]]s. When such roads are redesigned to incorporate roundabouts, traffic speeds must be reduced via tricks such as curving the approaches.

Many traffic circles have been converted to modern roundabouts, including the former [[Kingston, New York|Kingston]] traffic circle in New York and several in New Jersey.<ref>{{Cite web|url=http://www.state.nj.us/transportation/community/meetings/documents/handout031109.pdf|title=New Jersey roundabouts}}</ref><ref>{{cite news| url=https://www.nytimes.com/2007/11/25/nyregion/nyregionspecial2/25circlesnj.html?ref=automobiles | work=The New York Times | title=A Shift, but for Some Drivers, a Vicious Circle | first=Jill P. | last=Capuzzo | date=25 November 2007 | access-date=27 March 2010}}</ref> Others have been converted to signalised intersections, such as the Drum Hill Rotary in [[Chelmsford, Massachusetts]], which is now six lanes wide and controlled by four separate intersections.<ref>{{google maps|url=https://www.google.com/maps/preview#!q=42%C2%B0+37.347'%2C+-71%C2%B0+21.979'&data=!4m14!2m13!1m12!3m8!1m3!1d2055!2d-71.3661923!3d42.6221027!3m2!1i1044!2i1075!4f13.1!4m2!3d42.62245!4d-71.3663167|title=Drum Hill Rotary}}</ref>

Japan was first introduced to roundabouts in September 2014 to stop major accidents and traffic jams. <ref>{{Cite news |date=6 January 2020 |title=Roundabout opens in north Japan after lesson learned from 2011 quake, tsunami |language=en |work=Mainichi Daily News |url=https://mainichi.jp/english/articles/20200106/p2a/00m/0na/009000c#:~:text=In%20Japan,%20the%20revised%20Road,jams,%20possibly%20curbing%20serious%20accidents. |access-date=20 November 2023}}</ref>

=== Terminology ===
The word ''roundabout'' dates from early 20th-century use in the United Kingdom.<ref name="oxford" /> A ''roundabout'' is also a traditional English name given to amusement rides known as a [[carousel]], or a [[carousel|merry-go-round]] in other English-speaking countries.

In U.S. dictionaries the terms ''roundabout'', ''traffic circle'', ''road circle'' and ''rotary'' are synonyms.<ref name="dictionaries">[http://education.yahoo.com/reference/dictionary/entry/roundabout American Heritage] {{webarchive|url=https://web.archive.org/web/20131226235818/http://education.yahoo.com/reference/dictionary/entry/roundabout|date=26 December 2013}} ("roundabout: ''Chiefly British'' A traffic circle."), [http://dictionary.infoplease.com/roundabout Random House] ("roundabout: ''Chiefly Brit.'' See ''traffic circle''."), [http://www.merriam-webster.com/dictionary/roundabout Merriam-Webster]("roundabout, noun: ''British'': rotary 2"; "rotary 2: a road junction formed around a central circle about which traffic moves in one direction only—called also ''circle'', ''traffic circle'')[http://www.macmillandictionary.com/dictionary/british/roundabout Macmillan] "roundabout: a circular area where three or more roads meet that you have to drive around in one direction in order to get onto another road. The American word is ''traffic circle'' or ''rotary''.", [http://dictionary.cambridge.org/define.asp?key=68778&dict=CALD&topic=road-junctionsCambridge] ("roundabout: UK (US ''traffic circle'')), [https://archive.today/20130117081639/http://www.askoxford.com/concise_oed/rotary Concise Oxford] (rotary: N. Amer. a traffic roundabout.)</ref> However, several experts such as [[Leif Ourston]] have stressed the need to distinguish between the characteristics of the modern roundabout and the nonconforming traffic circle:<ref name="Ourston1995">{{Cite journal |last1=Ourston |first1=Leif |last2=Bared |first2=Joe G. |date=1995 |title=Roundabouts: A Direct Way to Safer Highways |url=https://books.google.com/books?id=Zl5RAQAAMAAJ&pg=RA1-PA41 |journal=Public Roads |publisher=Federal Highway Administration |volume=59 |issue=2 |pages=41–49 |access-date=20 October 2020}}</ref>

{{Columns-start}}
;Modern roundabout:
*Entering traffic yields to circulating traffic
*Entering traffic aims at the centre of the central island and is deflected slowly around it
*Upstream roadway often flares at entry, adding lanes
{{column}}
;Nonconforming traffic circle:
*Entering traffic cuts off circulating traffic
*Entering traffic aims to one side of the central island (right side for right-hand traffic) and proceeds straight ahead at speed
*Lanes are not added at entry
{{columns-end}}

The [[U.S. Department of Transportation]] adopted the term ''modern roundabout'' to distinguish those that require entering drivers to give way to others. Many old traffic circles remain in the [[Northeastern United States|northeastern US]].{{sfn|U.S. Department of Transportation|2013|loc=para 1.5}} Some modern roundabouts are elongated to encompass additional streets, but traffic always flows in a loop.

====Rotary====
In the United States, traffic engineers typically use the term ''rotary'' for large-scale circular junctions between [[Limited-access road|expressways]] or [[controlled-access highway]]s. Rotaries of this type typically feature high speeds inside the circle and on the approaches.<ref>{{cite web|url=http://safety.fhwa.dot.gov/intersection/roundabouts/presentations/safety_aspects/short.cfm|archive-url=https://web.archive.org/web/20140903014341/http://safety.fhwa.dot.gov/intersection/roundabouts/presentations/safety_aspects/short.cfm|url-status=dead|archive-date=3 September 2014|title=Safety Aspects of Roundabouts&nbsp;– FHWA Safety Program|date=3 September 2014|access-date=17 October 2018}}</ref>

In the United States' [[New England]] region, however, a "[[Rotaries in Massachusetts|rotary]]" is typically used as the general term for all roundabouts, including those with modern designs. State laws in these states mandate that traffic already driving in the rotary always has the right of way. For instance, in [[Massachusetts]], "Any operator of a vehicle entering a rotary intersection shall yield the right-of-way to any vehicle already in the intersection."<ref>{{cite web|url=https://malegislature.gov/Laws/GeneralLaws/PartI/TitleXIV/Chapter89/Section8|title=General Law&nbsp;– Part I, Title XIV, Chapter 89, Section 8|website=malegislature.gov|access-date=17 October 2018}}</ref> In [[Rhode Island]] entering vehicles "Yield to vehicles in the roundabout."<ref>{{cite web|url=http://www.dmv.ri.gov/documents/manuals/Driver_Manual_FINAL.pdf|title=Rhode Island Driver's Manual |website=Dmv.ri.gov|access-date=17 October 2018}}</ref>

====Other terms====
In the dialect of [[Dundee]] in Scotland, a roundabout is called a ''circle''.<ref>{{Cite web|title=Scottish words of the week: The Dundee dialect|first1=Peter|last1=Simpson|url=https://www.scotsman.com/arts-and-culture/scottish-words-week-dundee-dialect-1559097|access-date=3 August 2020|website=The Scotsman|date=4 October 2013 |language=en}}</ref>

In the English [[West Midlands (region)|West Midlands]], ''island'' is in common use.<ref>{{Cite web|title=Revealed: What is the most dangerous roundabout in Birmingham?|first1=Neil|last1=Elkes|first2=Patrick|last2=Scott|url=https://www.birminghammail.co.uk/news/midlands-news/revealed-what-most-dangerous-roundabout-11793448|access-date=15 September 2023|website=Birmingham Live|publisher=Reach plc|date=26 August 2016|language=en}}</ref>

In the [[Channel Islands]] a third type of roundabout, known as "Filter in Turn", exists.  Here approaching drivers neither give way to traffic on the roundabout, as normal, nor have priority over it, but take it in turns to enter from each. Almost all of [[Jersey]]'s roundabouts are of this type.<ref>{{Cite web|url=http://www.gov.je:80/Travel/Motoring/LearnerNewDrivers/Cars/Pages/TheoryTests.aspx|title=Driving tests and learning to drive or ride|first=States of|last=Jersey|website=gov.je}}</ref>

== Operation and design ==
{{more footnotes needed|section|date=December 2013}}
[[File:Elovainio shopping center roundabout - panoramio.jpg|thumb|A roundabout next to the Elovainio shopping centre in [[Ylöjärvi]], Finland]]
[[File:Rotatoria incorcio di Corso Italia, Via Roma e Via P.Micca nel centro di Legnano. 2015-02-22.jpg|thumb|An oval roundabout in [[Legnano]], Italy]]

The fundamental principle of modern roundabouts is that entering drivers give way to traffic within the roundabout without the need for traffic signals. Conversely, older traffic circles typically require circling drivers to give way to entering traffic. Roundabouts may also have an interior lane.<ref>{{cite book|url=http://safety.fhwa.dot.gov/intersection/roundabouts/fhwasa10006/|archive-url=https://web.archive.org/web/20100417120518/http://safety.fhwa.dot.gov/intersection/roundabouts/fhwasa10006/|url-status=dead|archive-date=17 April 2010|title=Intersection Safety Roundabouts – Safety – Federal Highway Administration|date=February 2010 |access-date=17 October 2018}}</ref> Generally, exiting directly from an inner lane of a multi-lane roundabout is permitted, given that the intersecting road has as many lanes as the roundabout. By contrast, exiting from an inner lane of an older traffic circle is usually not permitted and traffic must first move into the outside lane.

Vehicles circulate around the central island in one direction at speeds of {{convert|25|-|40|km/h|abbr=on|round=5|mph}}. In [[left-hand traffic]] countries they circulate [[clockwise]] (looking from above); in right-hand traffic, anticlockwise.

Multi-lane roundabouts are typically less than {{convert|75|m|round=10}} in diameter;<ref>{{cite web|url=http://www.ksdot.org/burtrafficeng/Roundabouts/Roundabout_Guide/Chapter_6_Geometric_Design.pdf |title=Kansas Roundabout Guide: A Supplement to FHWA's Roundabouts: An Informational Guide| author=Kittleson & Associates |work=Kansas Department of Transportation |access-date=26 August 2009}}</ref> older traffic circles and [[roundabout interchange]]s may be considerably larger. Roundabouts are roughly the same size as signalled intersections of the same capacity.

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 "the circle's historically established traffic flow pattern",<ref>{{cite web|url=https://www.state.nj.us/mvc/pdf/license/drivermanual.pdf |title=Driver manual |access-date=13 August 2021}}</ref> and there are no set rules. In [[New England]],<ref>{{cite web|url=http://www.mass.gov/rmv/dmanual/index.htm |title=Sharing the Road: A User's Manual for Public Ways |author=Commonwealth of Massachusetts, Registry of Motor Vehicles |access-date=13 May 2009}}</ref> [[Washington, D.C.]], and [[New York State]],<ref>{{cite web|url=http://safeny.com/rowa-vt.htm#1145|archive-url=https://web.archive.org/web/20110703061007/http://safeny.com/rowa-vt.htm#1145|url-status=dead|archive-date=3 July 2011|title=Vehicle & Traffic Law – Right of Way|date=3 July 2011|access-date=17 October 2018}}</ref> entering traffic yields, as is the norm in virtually all countries outside of the U.S.
* Angle of entry: Angles range from glancing ([[tangent]]ial) that allow full-speed entry to 90 degree angles ([[perpendicular]]).<ref name="ModernRoundabouts">{{cite web|url=https://www.fhwa.dot.gov/publications/research/safety/00067/index.cfm|title=Index – Roundabout: An Informational Guide, June 2000 – FHWA-RD-00-067|website=Fhwa.dot.gov|access-date=17 October 2018}}</ref> Deflection is required to avoid vehicles entering at excessive speeds.<ref>TSM https://en.wikisource.org/wiki/Traffic_Signs_Manual/Chapter_5/2009/8</ref>
* Traffic speed: High entry speeds (over {{convert|30|mph|km/h|abbr=on|disp=or}}) require circulating vehicles to yield, often stopping, which lowers capacity and increases crash rates compared to modern roundabouts.<ref>{{cite web|url=http://findarticles.com/p/articles/mi_qa3734/is_200703/ai_n18755716/pg_1 |title=A Comparative Evaluation of the Safety Performance of Roundabouts and Traditional Intersection Controls |author=Shashi S. Nambisan, Venu Parimi |date=March 2007 |work=Institute of Transportation Engineers |access-date=27 November 2007}}</ref>
* Lane changes: Allowed or not
* Diameter: The greater the traffic, the larger the circle.<ref name="ModernRoundabouts" />
* Island function: Parking, parks, fountains, etc.<ref name="ModernRoundabouts" />

=== Islands ===
[[File:LUMC-rotonde.JPG|thumb|Roundabout at [[Leiden University Medical Center]] in the Netherlands, with modern art animals on the central island, and an apron that can be used by large trucks.]]

Modern roundabouts feature a central island and sometimes pedestrian islands at each entry or exit often for decoration.

Denmark has begun widespread adoption of particular high islands, or if not possible, obstacles such as hedges or a ring of trees in larger examples. This is done to further increase the safety benefits of roundabouts, as the obstacles have been found to discomfort drivers more so than the roundabout itself compared to conventional intersections, thus initiating further observation and care taking of the driver. In Denmark, it was found to decrease accidents in roundabouts by 27% to 84% depending on height and type. In studies, heights of 0-0.9, 1-1.9 and 2+ metres were evaluated. It was found that for all heights, especially accidents leading to human injuries were reduced the most, by -47% to -84% for the aforementioned heights.<ref>{{Cite journal|last=Underlien Jensen|first=Søren|date=November 2012|title=Rundkørsler og trafiksikkerhed|url=https://www.trafitec.dk/sites/default/files/publications/rundk%20og%20trafiksikkerhed.pdf|journal=Trafik & Veje|language=Danish|pages=26–29}}</ref> The level of irritation to drivers is not to be understated, as it is the crucial point of the design: to force drivers to pay attention to the sides of the driving direction. This leads to drivers complaining about these designs, as Denmark in most regards embraces designing road infrastructure, such that the wanted driving behaviour leads to comfort i.e., lane width corresponding to speed limit and obstacles encouraging slowdown near points of safety concern such as schools. Such is the controversy for drivers that seasoned driving teachers complain about this discomfort a decade after its safety is proven and adoption widespread.<ref>{{Cite web|last1=sep 2020|first1=Clock 20|last2=Journalist|first2=kl 09:01 Bemærk: Artiklen er mere end 30 dage gammel Sebastian Myrup Hansen|title=Renovering af omdiskuteret rundkørsel er i gang - ikke godt nok mener kørelærer|url=https://www.tv2lorry.dk/solroed/renovering-af-omdiskuteret-rundkoersel-er-i-gang-ikke-godt-nok-mener-koerelaerer|access-date=27 January 2022|website=TV 2 Lorry|language=da}}</ref>

==== Central ====
[[File:La fontaine des trois Grâces, 1860.jpg|thumb|A fountain dominates this roundabout in [[Aix-en-Provence]], France.]]

The central island may be surrounded by a [[truck apron]] that is high enough to discourage drivers from crossing over it, but low enough to allow wide or long vehicles to navigate the roundabout. The island may provide a visual barrier, to alert approaching drivers to the presence of the roundabout, and to encourage drivers to focus on the traffic in the path of the circle. A visual barrier significantly reduces the accident rate.<ref>{{cite web |last1=Hansen |first1=Winnie |title=Spørg Fagfolket: Hvorfor skal øen i midten af rundkørslen være så høj? |url=https://ing.dk/artikel/spoerg-fagfolket-hvorfor-skal-oeen-midten-rundkoerslen-vaere-saa-hoej-225722 |website=[[Ingeniøren]] |publisher=[[Vejdirektoratet]] |language=da |date=2 June 2019 |quote=analysis of 332 roundabouts. It was very clear that if the height in the middle of the roundabout was over two meters, then it was much safer than other designs. The accident rate was significantly lower in the high roundabouts}}</ref> Otherwise, vehicles anywhere in or near the circle can cause those <!--inexperienced-->entering to stop and wait for them to pass, even if they are opposite, which unnecessarily reduces traffic flow. The barrier may be a landscaped mound, a raised wall, a tree or tall shrubs. Road signage or flagpoles may be erected at the top of a landscaped mound.

Some communities use the island for monuments, the display of large public art or for a fountain. Pedestrians may be prohibited from crossing the circling lane(s). Access to the central island requires an underpass or overpass for safety.

===== Art installations =====
[[File:Guadalajara, Jalisco, Mexico (2021) - 050.jpg|thumb|The [[Statue of Minerva, Guadalajara|Minerva Roundabout]] in [[Guadalajara]], Mexico]]
Roundabouts have attracted art installations around the world:
* [[Bend, Oregon]] (United States); Bend's roundabout sculptures were honoured by [[Americans for the Arts]] as among the 37 most innovative approaches to Public Art in the country.<ref>{{cite web|title=Art In Public Places, Bend, Oregon|url= http://artinpublicplaces.org/history.php |publisher=Art in Public Places|access-date=2 November 2013|archive-url= https://web.archive.org/web/20080509071110/http://artinpublicplaces.org/history.php |archive-date=9 May 2008|url-status=dead}}</ref><ref>{{cite web|title=Pillar of art|url=http://artinpublicplaces.org/files/VisitBend-RndAbtmap.pdf |publisher=Art in Public Places|access-date=2 November 2013|archive-url= https://web.archive.org/web/20131103202747/http://artinpublicplaces.org/files/VisitBend-RndAbtmap.pdf |archive-date=3 November 2013|url-status=dead}}</ref>
* [[Fuerteventura]], Canary Islands (Spain); Local government displayed sculptures at several roundabouts.<ref>{{cite web|title=Fuerteventura, art on the roads: roundabouts as galleries|date= 2 July 2012 |url= http://robertoalborghetti.wordpress.com/2012/07/02/art-on-the-roads-roundabouts-as-galleries-my-days-in-fuerteventura-5/ |publisher=Roberto Alborghetti|access-date=2 November 2013}}</ref>
* Many countries in Europe (France first,<ref>{{google maps|url=https://www.panoramio.com/map/?group=13339#lt=47.334499&ln=2.209236&z=11&k=0&a=1&tab=6&pl=all|title=Photographs of French roundabouts}}</ref> but also Germany,<ref name="North_Europe">{{google maps|url=https://www.panoramio.com/map/?group=13339#lt=50.912865&ln=10.075447&z=11&k=0&a=1&tab=6&pl=all |title=Roundabout photographs from The Netherlands, Belgium, Germany and Austria}}</ref> Austria,<ref name="North_Europe"/> Italy,<ref>{{google maps|url= https://www.panoramio.com/map/?group=13339#lt=42.710044&ln=11.261970&z=11&k=0&a=1&tab=6&pl=all |title=Roundabout photographs from Italy}}</ref> Spain,<ref>{{google maps|url= https://www.panoramio.com/map/?group=13339#lt=39.938544&ln=-3.239983&z=11&k=0&a=1&tab=6&pl=all |title=Roundabout photographs from Spain}}</ref> and others<ref name="North_Europe"/>) show the widespread use of roundabouts as art installations.<ref name="Panoramio_Roundabouts">{{cite web|title=Unusual road roundabouts: artistic, and otherwise. A collection of more than 2000 photographs, by almost 200 amateur photographers, from all over the world|url=https://www.panoramio.com/group/roundabouts|work=Panoramio: Roundabouts|publisher=www.panoramio.com|access-date=2 November 2013|archive-url=https://web.archive.org/web/20131103061756/http://www.panoramio.com/group/roundabouts|archive-date=3 November 2013|url-status=dead}}</ref><ref>{{cite news|title=Roundabout / Kreisverkehr – streets with a roundabout / Straßen mit einem Kreisverkehr|newspaper=Flickr |url=https://www.flickr.com/groups/350203@N21/|publisher=www.flickr.com|access-date=2 November 2013|language=en, de}}</ref>
* An inventory of roundabouts in France, made by Marc Lescuyer, listed 3,328 roundabouts with artistic decor early in 2010.<ref name="Panoramio_Roundabouts"/><ref>{{cite web|title=Inventory of French roundabouts|url= http://www.marclescuyer.fr/textesrp/pagetype.htm |publisher=Marc Lescuyer|access-date=1 January 2010|language=fr|url-status=dead|archive-url= https://web.archive.org/web/20081111032348/http://www.marclescuyer.fr/textesrp/pagetype.htm |archive-date=11 November 2008}}</ref>
* The [[Statue of Minerva, Guadalajara|Minerva Roundabout]] in [[Guadalajara]], Mexico, is one of the city's most famous monuments. It features the goddess [[Minerva]] standing on a pedestal, surrounded by a large fountain, with an inscription saying "Justice, wisdom and strength guard this loyal city".
* Several famous monuments in Europe, such as the [[Puerta de Alcalá|Gate of Alcalá]] in [[Madrid]], Spain or the [[Arc du Triomphe]] in [[Paris]], France, have been isolated from street traffic by means of a roundabout.
* The [[Garces Memorial Circle]] in [[Bakersfield, California]] contains a statue to Father [[Francisco Garces]].
* In the [[Philippines]], the town of [[Ipil, Zamboanga Sibugay]] has an Obelisk containing art and the [[Baybayin]] script.

==== Pedestrian ====
[[File:View2FromPearlTower.jpg|thumb|This roundabout in [[Shanghai]], China, has a pedestrian bridge in the form of another, raised roundabout.]]

For larger roundabouts, pedestrian islands at each entry/exit encourage drivers to slow and prepare to enter the circle. They also provide a refuge where pedestrians may pause mid-crossing.
Vehicles or bicycles entering or exiting the roundabout must yield to all traffic including pedestrians.<ref>{{Cite web|url=https://www.dmv.ca.gov/portal/handbook/california-driver-handbook/laws-and-rules-of-the-road/|title=Section 7: Laws and Rules of the Road|website=California DMV}}</ref>

=== Pedestrian crossing ===
[[Pedestrian crossing]]s at each entry/exit may be located at least one full car length outside the circle. The extra space allows pedestrians to cross behind vehicles waiting to enter the circle, and to allow exiting vehicles to stop for pedestrians without obstruction. Each pedestrian crossing may traverse a [[pedestrian island]] for protection that also forces drivers to slow and begin to change direction, encouraging slower, safer speeds. On the island, the pedestrian crossing may become diagonal, to direct the gaze of those crossing into exiting traffic.

=== Bicycles ===
Physically separated bikeways best protect cyclists.<ref name="swov-roundabouts">{{Cite web|url=https://swov.nl/en/facts-figures|title=Facts & figures|website=swov.nl}}</ref><ref name="modern" /><ref>{{Cite web|url=https://mutcd.fhwa.dot.gov/HTM/2003/part3/part3b2.htm|title=FHWA - MUTCD - 2003 Edition Chapter 3B2|website=[[Federal Highway Administration|Federal Highway Administration (FHWA)]]}}</ref> Less optimally, terminating cycle lanes well before roundabout entrances requires cyclists to merge into the stream of motor traffic, but keeps cyclists in full view of drivers, at some cost in motor vehicle speed. Cyclists may also be permitted to use pedestrian crossings. 

Traditional cycle lanes increase vehicle–bicycle collisions. When exiting, a motorist must look ahead to avoid colliding with another vehicle or with pedestrians on a pedestrian crossing. As the intersection curves away from the exit, the path of an exiting vehicle is relatively straight, and so the motorist may often not slow substantially. To give way to a cyclist on the outside requires the exiting motorist to look toward the rear, to the perimeter. Other vehicles can obstruct the driver's view in this direction, complicating the motorist's task. The more frequent requirements for motorists to slow or stop reduce traffic flow. A 1992 study<ref>R. Schnüll, J. Lange, I. Fabian, M. Kölle, F. Schütte, D. Alrutz, H.W. Fechtel, J. Stellmacher-Hein, T. Brückner, H. Meyhöfer: ''Sicherung von Radfahrern an städtischen Knotenpunkten'' [''Safeguarding bicyclists in Urban Intersections''], Bericht der Bundesanstalt für Straßenwesen zum Forschungsprojekt 8952, 1992</ref> found that the risk to cyclists is high in all such intersections, but much higher when the junction has a marked bicycle lane or sidepath around its perimeter.<ref>[http://bernd.sluka.de/Radfahren/Vortragsfolien.html Vortragsfolien Radverkehr] Scroll to the section labelled "''Kreisverkehr''". A translation of the text reads: Graphic from ''Sicherung von Radfahrern an städtischen Knotenpunkten'' [''Safeguarding cyclists in Urban Intersections''], (BASt, 1992). Accident numbers in large circular junctions with different bicycle facilities show: 1. Why there should be no pathways or bike lanes at these junctions; 2. Even when cyclists use the roadway, their risk is relatively high at these junctions.</ref><ref>Maycock, G., and Hall, R. D. (1984). "Accidents at 4-Arm Roundabouts." TRRL1120, Transport and Road Research Laboratory (TRRL), Crowthorne, England.</ref> Cycle lanes were installed at Museum Road, [[Portsmouth]], but were replaced by a narrowed [[carriageway]] to encourage lane sharing.

The roundabout at the [[Arizona State Route 202#Exit list|Brown Road and Loop 202]] interchange in [[Mesa, Arizona]], adopts a U.S.-recommended design.<ref name="adot">{{Cite web|url=https://azdot.gov/about/transportation-safety/roundabouts|title=Roundabouts &#124; ADOT|website=azdot.gov}}</ref> On-street road markings direct cyclists to enter the pavement at the end of the bike lane. Cyclists who choose to travel on the wide pavement, cross roundabout arms perpendicularly, well outside the circle. A pedestrian island allows pedestrians and cyclists to cross one lane at a time.

[[Dutch roundabout|Protected roundabouts]] (or Dutch roundabout) were developed in the [[Netherlands]], with cyclists separated from vehicles using dedicated lanes.<ref name=":0">{{Cite book |url=https://www.worldcat.org/oclc/972096448 |title=Design manual for bicycle traffic |date=2016 |others=Rik de Groot, vervoer en infrastructuur CROW kenniscentrum voor verkeer |isbn=978-90-6628-659-7 |location=Ede, The Netherlands |pages=147–148 |oclc=972096448}}</ref> As cyclists will conflict with motorists at the exit arms of the motorised roundabout, priority must be established. In the Netherlands, cyclists will normally be given priority to [[Bicycle-friendly|promote cycling]] over driving.<ref name=":0" /> As well as their use in the Netherlands and Denmark, these designs have been subsequently built in the United Kingdom and Ireland.<ref>{{Cite web |date=7 August 2020 |title=UK's first Dutch-style roundabout welcomed by road safety campaigners - Highways Industry |url=https://www.highwaysindustry.com/uks-first-dutch-style-roundabout-welcomed-by-road-safety-campaigners/ |access-date=29 July 2024 |website=Highways Industry |language=en-US}}</ref><ref>{{Cite web |date=29 May 2023 |title=Ireland's first Dutch-style roundabout opened in Dublin 15 - |url=https://irishcycle.com/2023/05/29/irelands-first-dutch-style-roundabout-opened-in-dublin-15/ |access-date=29 July 2024 |website=IrishCycle.com |language=en-GB}}</ref>

<gallery widths="200" heights="200" class="center">
File:Okay to enter sidewalk.jpg|alt=Pavement markings indicate sidewalk riding is legal.|Road markings invite cyclists to enter the pavement on approach to roundabout in [[Mesa, Arizona]]. Cyclists are still permitted to use the roundabout like any other vehicle.
File:Bicyclist in roundabout.jpg|alt=Cyclist rides through the main lane of roundabout|Cyclists can choose to ride on the pavement on far right, or in the main lanes of this roundabout in Mesa, Arizona.
File:Protected roundabout 3D.png|3D view of a [[Protected intersection|protected roundabout]], as commonly used in the Netherlands
</gallery>

=== Capacity and delays ===
[[File:ChivertonCrossRoundaboutA30Cornwall.jpg|thumb|Traffic approaching Chiverton Cross roundabout in Cornwall, UK]]

The capacity of a roundabout varies based on entry angle, lane width, and the number of entry and circulating lanes. As with other types of junctions, operational performance depends heavily on the flow volumes from various approaches. A single-lane roundabout can handle approximately 20,000–26,000 vehicles per day, while a two-lane design supports 40,000 to 50,000.<ref name="modern">{{cite web|title=Modern Roundabouts, an Informational Guide|url=https://www.fhwa.dot.gov/publications/research/safety/00068/|website=Federal Highway Administration Research and Technology|access-date=15 September 2015}}</ref>

Under many traffic conditions, a roundabout operates with less delay than signalised or [[all-way stop]] approaches. Roundabouts do not stop all entering vehicles, reducing both individual and queuing delays. Throughput further improves because drivers proceed when traffic is clear without waiting for a signal to change.

Roundabouts can increase delays in locations where traffic would otherwise often not be required to stop. For example, at the junction of a high-volume and a low-volume road, traffic on the busier road would stop only when cross traffic was present, otherwise not having to slow for the roundabout. When the volumes on the roadways are relatively equal, a roundabout can reduce delays, because half of the time a full stop would be required. Dedicated left turn signals (in countries where traffic drives on the right) further reduce throughput.

Roundabouts can reduce delays for pedestrians compared to traffic signals, because pedestrians are able to cross during any safe gap rather than waiting for a signal. During peak flows when large gaps are infrequent, the slower speed of traffic entering and exiting can still allow crossing, despite the smaller gaps.

Studies of roundabouts that replaced stop signs and/or traffic signals found that vehicle delays were reduced 13–89 percent and the proportion of vehicles that stopped was reduced 14–56 percent. Delays on major approaches increased as vehicles slowed to enter the roundabouts.<ref name="iihs"/>

Roundabouts have been found to reduce [[carbon monoxide]] emissions by 15–45 percent, [[nitrous oxide]] emissions by 21–44 percent, [[carbon dioxide]] emissions by 23–37 percent and [[hydrocarbon]] emissions by 0–42 percent. Fuel consumption was reduced by an estimated 23–34 percent.<ref name=iihs/>

==== Capacity modelling ====
Many countries have researched roundabout capacity. The software can help calculate capacity, delay and queues. Packages include [[ARCADY]], Rodel, Highway Capacity Software and [[Sidra Intersection]]. ARCADY and Rodel are based on the Transport Research Laboratory mathematical model. The TRL approach is derived from empirical models based on geometric parameters and observed driver behaviour with regard to lane choice. Sidra Intersection software includes roundabout capacity models developed in Australia and the US.

Research on Australian roundabouts was conducted in the 1980s at the Australian Road Research Board (ARRB).<ref>{{cite book|url=http://www.arrb.com.au/Information-services/Publications.aspx|title=Effectiveness Audit of ARRB Intersection Capacity Research|location=Research Report ARR 242. ARRB Transport Research Ltd, Vermont South, Australia|author=Taylor, M.P., Barton, E.V., Bliss, J. and O'Brien, A.P. (1993)|url-status=dead|archive-url=https://web.archive.org/web/20160227020155/https://arrb.com.au/Information-services/Publications.aspx|archive-date=27 February 2016}}</ref> Its analytical capacity and performance models differ from the TRL model significantly, following a lane-based gap-acceptance theory including geometric parameters.

Research on U.S. roundabouts sponsored by the [[Transportation Research Board]] (TRB) and [[Federal Highway Administration]] (FHWA) culminated in a capacity model that was included in the ''[[Highway Capacity Manual]]'' (HCM) Edition 6<ref>{{cite book|url=http://www.trb.org/publications/hcm6e.aspx|title=Highway Capacity Manual, Sixth Edition: A Guide for Multimodal Mobility Analysis|author=TRB (2016)|location= Transportation Research Board, National Research Council, Washington, DC, US}}</ref> and the ''TRB-FHWA Roundabout Informational Guide'' ([[NCHRP]] Report 672).<ref>{{cite book|url=http://www.trb.org/Main/Blurbs/164470.aspx|title=Roundabouts: An Informational Guide |author=TRB|date=2010 |location=NCHRP Report 672. Transportation Research Board, National Research Council, Washington, D.C., US, in cooperation with US Department of Transportation, Federal Highway Administration|doi=10.17226/22914 |isbn=978-0-309-15511-3 }}</ref> The HCM Edition 6 model is based on lane-based gap-acceptance theory. A recent NCHRP survey of US state transport agencies found that [[Sidra Intersection]] is the most widely used software tool in the US for roundabout analysis.<ref>{{cite book|url=https://www.nap.edu/catalog/23477/roundabout-practices|title=''Roundabout Practice, A Synthesis of Highway Practice''|publisher=  Transportation Research Board|year=2016|location=National Cooperative Highway Research Program, NCHRP SYNTHESIS 488. Washington DC, US.|doi=10.17226/23477|isbn=978-0-309-27208-7 |last1=Pochowski |first1=Alek |last2=Paul |first2=Andy |last3=Rodegerdts |first3=Lee A. }}</ref>

== Safety ==
{{See also|Traffic calming}}
[[File:Roundabout intersection diagram.svg|thumb|A comparison of possible collision points on a roundabout versus a traditional intersection]]
[[File:2008 03 12 - UMD - Roundabout viewed from Art Soc Bldg 4.JPG|thumb|Small modern roundabout in the United States, where vehicles are driven on the right]]
[[File:DiamondRoundabout.jpg|thumb|Roundabout in the United States with separated side lanes. Vehicles entering the roundabout give way to vehicles in the roundabout.]]
[[File:CarlandCrossRoundaboutA30Cornwall.jpg|thumb|A typical [[trunk road#United Kingdom|trunk road]] roundabout in the UK at [[Carland Cross]] on the [[A30 road|A30]] in [[Cornwall]], United Kingdom. There is a free-flow lane for the A30 towards [[Bodmin]] (nearest the camera).]]

Statistically, modern roundabouts are safer for drivers and pedestrians than both older-style traffic circles and traditional intersections.<ref>{{cite journal |title=A Comparative Evaluation of the Safety Performance of Roundabouts and Traditional Intersection Controls |first1=Shashi S. |last1=Nambisan |first2=Venu |last2=Parimi |date=March 2007 |journal=Institute of Transportation Engineers }}</ref> Compared with these other forms of intersections, modern roundabouts experience 39% fewer vehicle collisions, 76% fewer injuries and 90% fewer serious injuries and fatalities (according to a study of a sampling of roundabouts in the United States, when compared with the junctions they replaced).<ref>{{Cite web |url=https://www.k-state.edu/roundabouts/news/sr3505.pdf |title=Status Report |access-date=9 June 2014 |archive-url=https://web.archive.org/web/20140714142530/https://www.k-state.edu/roundabouts/news/sr3505.pdf |archive-date=14 July 2014 |url-status=dead }}</ref> At junctions with stop signs or traffic lights, the most serious accidents are right-angle, left-turn or head-on collisions where vehicles move fast and collide at high impact angles, e.g. head-on. Roundabouts virtually eliminate those types of crashes. Instead, most crashes are glancing blows at low angles of impact.<ref name="Richtmeyer">{{cite news | first=Richard | last=Richtmeyer | title=Safer Roundabouts Sprouting Up All Over New York, Nation | publisher=Associated Press | url=https://www.boston.com/news/local/connecticut/articles/2008/01/06/safer_roundabouts_sprouting_up_all_over_new_york_nation/ | archive-url=https://archive.today/20121215020745/http://www.boston.com/news/local/connecticut/articles/2008/01/06/safer_roundabouts_sprouting_up_all_over_new_york_nation/ | url-status=dead | archive-date=15 December 2012 | date=6 January 2008 | access-date=10 January 2008 }}</ref><ref>{{cite web|url=http://www.iihs.org/iihs/topics/t/roundabouts/topicoverview|title=Roundabouts - Topic overview|publisher=Insurance Institute for Highway Safety}}</ref> Further, a study based on satellite imagery of all intersections in Australia observed consistently low speeds on roundabouts compared to other intersection types, contributing to reduced injury severity in case of a crash.<ref>{{cite journal |last1=Wijnands |first1=J.S. |last2=Zhao |first2=H. |last3=Nice |first3=K.A. |last4=Thompson |first4=J. |last5=Scully |first5=K. |last6=Guo |first6=J. |last7=Stevenson |first7=M. |title=Identifying safe intersection design through unsupervised feature extraction from satellite imagery |journal=Computer-Aided Civil and Infrastructure Engineering |year=2020 |volume=36 |issue=3 |pages=346–361 |doi=10.1111/mice.12623|arxiv=2010.15343 |s2cid=225103031 }} [https://onlinelibrary.wiley.com/doi/epdf/10.1111/mice.12623 PDF]</ref>

Some larger roundabouts take foot and bicycle traffic through [[underpass]]es or alternate routes. However, an analysis<ref>Wilke, A. and Koorey, G. (2001). ''How Safe are Roundabouts for Cyclists?'' In TranSafe Issue 5, April 2001. Wellington, NZ. [http://viastrada.co.nz/sites/viastrada/files/Transafe_05.pdf PDF] {{webarchive|url=https://web.archive.org/web/20081015101010/http://viastrada.co.nz/sites/viastrada/files/Transafe_05.pdf |date=15 October 2008 }}</ref> of the New Zealand national crash database<ref>{{cite web|url=http://www.landtransport.govt.nz/research/cas/|title=Crash analysis system|access-date=29 November 2007}}</ref> for the period 1996–2000 shows that 26% of cyclists reported injury crashes happened at roundabouts, compared to 6% at traffic signals and 13% at priority controlled junctions. The New Zealand researchers propose that low vehicle speeds, circulatory lane markings and mountable centre aprons for trucks can reduce the problem.<ref>Campbell, D., Jurisich, I., Dunn, R. 2006. ''Improved multi-lane roundabout designs for cyclists.'' Land Transport New Zealand Research Report 287. 140 pp. [http://www.landtransport.govt.nz/research/reports/287.pdf PDF]</ref> The most common roundabout crash type for cyclists, according to the New Zealand study, involves a motor vehicle entering the roundabout and colliding with a cyclist who already is travelling around the roundabout (more than half of cyclist/roundabout crashes in New Zealand fall into this category). The next most common crash type involves motorists leaving the roundabout colliding with cyclists who are continuing farther around the perimeter.

=== Vision-impaired pedestrians ===
Poorly designed walkways increase risks for the vision-impaired, because it is more difficult than at a signalised intersection to audibly detect whether there is a sufficient gap in traffic to cross safely. At a signalised intersection, traffic comes to a stop, and an audible sound can be generated to indicate that it is time to cross.<ref>Pedestrian Access to Modern Roundabouts: Design and Operational Issues for Pedestrians who are Blind [http://www.access-board.gov/research/roundabouts/bulletin.htm, retrieved 6/26/2010 access-board.gov] {{webarchive |url=https://web.archive.org/web/20120331234233/http://www.access-board.gov/research/roundabouts/bulletin.htm |date=31 March 2012 }}</ref>

This issue has led to a conflict in the United States between the vision-impaired and [[civil engineering]] communities. One solution is to provide manually-operated pedestrian crossing signals at each entry. This increases construction and operation costs, and requires some way to disrupt traffic long enough for the pedestrian to cross (such as a [[HAWK beacon]]) that defeats the purpose of the roundabout. Signalisation also increases delays for most pedestrians during periods of light traffic, since pedestrians need to wait for a signal to change before (legally) crossing.<ref>Bill Baranowski, P.E., [http://www.teachamerica.com/roundabouts/RA057A_ppr_Baranowski.pdf Pedestrian Crosswalk Signals at Roundabouts: Where are they Applicable?]</ref>

Signalised pedestrian crossings are normally used on large-diameter roundabout interchanges rather than small-diameter modern roundabouts.

== Types of circular intersections ==
[[File:Putrajaya_roundabout_aerial_view.jpg|thumb|upright|The world's largest roundabout, the [[Persiaran Sultan Salahuddin Abdul Aziz Shah, Putrajaya|Persiaran Sultan Salahuddin Abdul Aziz Shah]], at [[Putrajaya]], Malaysia<ref>{{Cite web|url=http://guinnessworldrecords.com/world-records/100371-largest-roundabout|title=&#124; Guinness World Records}}</ref>]]
{{mos|date=October 2021}}
Large roundabouts, such as those used at motorway junctions, typically have two to six lanes and may include traffic lights to regulate flow.

Some roundabouts have a divider or subsidiary deflection island, by means of which is provided a "free flow" segregated left- (or right-) turn lane (for the UK see [[Design Manual for Roads and Bridges]] TD 51/03) between traffic moving between two adjacent roads, and traffic within the roundabout, enabling drivers to bypass the roundabout.

=== Gyratory system ===
The term "gyratory" (for example, [[Hanger Lane gyratory]]) is sometimes used in the United Kingdom for a large circular intersection with non-standard lane markings or priority arrangements, or where there are significant lengths of carriageway between the entry arms, or when buildings occupy the central island.<ref>{{cite web|url=http://www.alaskaroundabouts.com/history.html|title=History of Roundabouts|access-date=29 November 2007|archive-url=https://web.archive.org/web/20080127234652/http://www.alaskaroundabouts.com/history.html|archive-date=27 January 2008|url-status=dead}}</ref>

In the 21st century several gyratory systems in London have been removed, including Tottenham Hale<ref>Transport for London https://tfl.gov.uk/info-for/media/press-releases/2014/november/tottenham-hale-improvement-works-complete</ref> and [[Elephant and Castle]].

=== Smaller, small and mini-roundabouts ===
{{anchor|mountable apron}}
[[File:Waterloo, Ontario, mini-roundabout at Union Street East and Margaret Avenue South.jpg|thumb|A small roundabout in [[Waterloo, Ontario]], Canada]]

As the overall or external size of a roundabout (in the UK referred to as the Inscribed Circle Diameter – ICD) is reduced, the maximum practicable (and prescribed) diameter for the central island is also reduced, whilst the width of the circulatory carriageway increases (due to the greater width of the vehicle swept path at smaller turning radii). In most cases, this results in it being too easy – certainly when traffic is light relative to capacity – for drivers to traverse the roundabout at relatively high speed, with scant regard for road markings or the potential dangers to self or conflicts with other road users. To mitigate this risk, a proportion of the circulatory carriageway – an annulus around the central island – is segregated from general use by demarcation lines and differentiated from the outer annulus of the carriageway by a combination of a slightly raised surface, adverse crossfall, contrasting colours and textures and demarcating lines. The effect of this is to discourage drivers from taking a more direct path through the roundabout, their line of least resistance is more tightly curved (and therefore slower) but more bearable. The inner annulus provides for the trailing axles of longer or articulated vehicles to sweep across the inner annulus, which is therefore known as an over-run area (in UK usage), truck apron, or mountable apron.

The smaller the roundabout, the more such mitigation measures are likely to be abused – the less effective they will be. In the UK the minimum size for roundabouts with raised islands is 28 metre diameter ICD with a 4-metre diameter island. This threshold being driven primarily by vehicle geometry – which is globally relatively consistent – rather than driver behaviour, it is adopted in other jurisdictions too. Below this minimum size, the mini-roundabout prevails.

=== Mini-roundabouts ===
After developing the offside priority rule, [[Frank Blackmore (traffic engineer)|Frank Blackmore]], of the UK's [[Transport Research Laboratory]], turned his attention to the possibility of a roundabout that could be built at sites lacking room for a conventional roundabout.<ref name="Obit-Fank_Blackmore">{{cite news | url=https://www.theguardian.com/theguardian/2008/jun/21/6 | title=Frank Blackmore Determined, maverick traffic engineer who invented the mini-roundabout | work=[[The Guardian]] | date=21 June 2008 | access-date=7 October 2013 | last=Rhodes | first=Belinda}}</ref>
{{Gallery
| align        =right
| height       =113
| width        =200
| File:Small roundabout. Kargilik.jpg
 | <small>Small roundabout in [[Kargilik Town|Kargilik]], Xinjiang, China</small>
 | alt2=
| File:Germany, Sachsen-Anhalt, Südharz, Uftrungen (1).JPG
 | <small>Mini-roundabout in [[Uftrungen]], Germany</small>
 | alt3=
| File:mini-roundabout.jpg
 | <small>A mini-roundabout in the UK, where a painted white circle is used as centre. The arrows show the direction of traffic.</small>
 | alt1=
}}
[[File:Qatar, Simaisma (9), roundabout with shops.JPG|thumb|right|Roundabout in rural [[Qatar]]]]
Mini-roundabouts can incorporate a painted circle or a low dome but must be fully traversable by vehicles. Motorists can drive over them when there is no other traffic, but it is dangerous to do so otherwise. Once the practice is established it may be difficult to discourage. Mini-roundabouts use the same right-of-way rules as standard roundabouts but produce different driver behaviour. Mini-roundabouts are sometimes grouped in pairs (a double mini-roundabout) or in "chains", simplifying navigation of otherwise awkward junctions. In some countries [[road sign]]s distinguish mini-roundabouts from larger ones.

Mini-roundabouts are common in the UK, Ireland and [[Hong Kong]] (particularly on Hong Kong Island), as well as [[Irapuato, Guanajuato|Irapuato]] in Mexico.

In the UK and also in other jurisdictions that have adopted mini-roundabouts, to drive across the central disc or dome when it is practicable to avoid it is an offence. Vehicles are required to treat the painted circle as if it were a solid island and drive around it.<ref>{{cite web|url=http://www.direct.gov.uk/en/TravelAndTransport/Highwaycode/DG_070338|title=The Highway Code – Roundabouts|access-date=14 May 2009}} Section 188, referring to Road Traffic Act 1988, Section 36, and [http://www.opsi.gov.uk/si/si2002/20023113.htm Traffic Signs Regulations & General Directions 2002], Regulations 10(1) & 16(1)</ref> Some local authorities paint double white lines around the circle to indicate this, but these require permission from the [[Secretary of State for Transport]]. The central dome also must be able to be overrun by larger vehicles.

In the UK – and also in other highway jurisdictions – the maximum size (inscribed circle diameter) for a mini roundabout is 28 metres (30 yards).{{Citation needed|date=January 2025}}

===Raindrop roundabouts===
<!-- This section is linked from [[Raindrop interchange]]. -->
These roundabouts do not form a complete circle and have a "[[wiktionary:raindrop|raindrop]]" or "[[wiktionary:teardrop|teardrop]]" shape. They have also been used at [[bowtie (road)|bowtie]] intersections, replacing traffic signals that are inefficient without a turning lane. In addition to their use at intersections, raindrop roundabouts are also used in [[dogbone interchange]]s (described [[#Motorways|below]]).
{{Clear}}

===Balcony roundabout===
A balcony roundabout is just an elevated roundabout. They are constructed in such a way that vulnerable road users can cross underneath the roundabout. Footpaths and cycle paths along the different roads connect to the square under the roundabout. Vulnerable road users do not interfere with motorised traffic on the roundabout, reducing the risk of collision.

=== Turbo roundabouts ===
[[File:Turborotonde.svg|thumb|A turbo roundabout design commonly found in the Netherlands]]

In the [[Netherlands]], [[Belgium]], [[Bosnia and Herzegovina]], [[the United Kingdom]], [[Finland]], [[Spain]], [[Poland]], [[Hungary]], [[Slovenia]], [[Slovakia]], the [[Czech Republic]], [[North Macedonia]], [[Croatia]], [[Germany]], and the U.S. states of [[Alabama]],<ref>{{cite news |last1=Chatman |first1=Bria |title=Jefferson County welcomes nation's 3rd 'turbo' roundabout |url=https://www.wbrc.com/2025/02/05/jefferson-county-welcomes-nations-3rd-turbo-roundabout |access-date=5 February 2025 |publisher=WBRC |date=5 February 2025}}</ref> [[California]], and [[Florida]], a relatively new type of two-lane roundabout designs is emerging, called "turbo roundabouts". These designs require motorists to choose their direction before entering the roundabout, thereby eliminating many conflicting paths and choices on the roundabout itself so that traffic safety is increased, as well as speed and capacity. These designs, seen from above, typically result in a spiralling flow of traffic. One minor drawback is that turbo roundabouts are often marked out such that a U-turn by means of the roundabout is not possible for drivers approaching on certain arms.

Several variations of turbo roundabouts exist. They are frequently designed for the intersection of a major road crossing a road with less traffic.

An early application of the principle was a six-arm and therefore relatively large (and fast) non-circular roundabout at [[Stairfoot]], Barnsley, South Yorkshire, which was given spiral marking about 1984. At that time the method was considered experimental and needed special consent from central authorities. The turbo roundabout was formally developed in 1996 in the Netherlands by Lambertus Fortuijn, a researcher from the [[Delft University of Technology]].<ref>{{ cite web | url = http://repository.tudelft.nl/view/ir/uuid:e01364ce-78de-465b-a8c8-39e28a4585dd/ | publisher = [[Delft University of Technology]] | title = Turborotonde en turboplein: ontwerp, capaciteit en veiligheid | trans-title = Turbo Roundabout and Turbo Circle; Design, Capacity and Safety | date = 8 January 2013 | access-date = 16 October 2014 | language = nl}}</ref> Similar roundabouts, with spiralling lane markings, have been used for many years in the UK e.g. the A176/A127 (eastbound) at [[Basildon]], Essex ({{coord|51.561399|n|0.452934|e}}). However, it was not until 1997 that the UK's national highway authorities published guidance (DMRB TA-78/97) that in effect endorsed the use of spiral markings in certain circumstances.

Turbo roundabouts can be built with raised lane separators (common in the Netherlands<ref>{{Cite web |url=https://www.crow.nl/publicaties/turborotondes |title=Turborotondes - CROW |access-date=9 July 2017 |archive-url=https://web.archive.org/web/20170926142941/http://www.crow.nl/publicaties/turborotondes |archive-date=26 September 2017 |url-status=dead }}</ref>) or with lane markings only. The use of raised lane separators prevents road users from weaving (thereby reducing conflicts) but can make manoeuvring more difficult for large vehicles.

[[File:Two-lane_roundabout_and_turborondabout_intersection_diagram.svg|thumb|A comparison between a two-lane roundabout and a turbo roundabout showing possible collision points.]]

According to simulations, a two-lane roundabout with three exits should offer 12–20% greater traffic flow than a conventional, three-lane roundabout of the same size. The reason is reduced weaving that makes entering and exiting more predictable. Because there are only ten points of conflict (compared with 8 for a conventional single lane roundabout, or between 32 and 64 with traffic signal control), this design is often safer as well. Research and experiments show that traffic accidents are reduced by 72% on turbo roundabouts compared to multi-lane roundabouts, which have 12 points of conflict.<ref>{{ cite web | url = http://www.turboroundabout.com/benefits.html | publisher = Transoft Solutions Inc. | title = Benefits of Turboroundabouts | date = 2014 | access-date = 16 October 2014 }}</ref> Research at [[Windesheim University of Applied Sciences|Windesheim University]] also shows that turbo roundabouts reduce accidents including casualties by some 75% when compared to regular intersections, and by 61% compared to single-lane roundabouts.<ref name="Windesheim">{{cite web |url=http://www.dirkdebaan.nl/blog/effecten-realisatie-turborotonde-onderzocht |title=Effecten realisatie turborotonde onderzocht |language=nl |trans-title=Effects research of turbo roundabouts |last=Vos |first=Christiaan |date=31 January 2016 |website=Verkeer – Verkeersveiligheid – Vorm (Traffic, Safety, Form) |publisher=Dirk de Baan |access-date=28 January 2017 |archive-url=https://web.archive.org/web/20170128152605/http://www.dirkdebaan.nl/blog/effecten-realisatie-turborotonde-onderzocht |archive-date=28 January 2017 |url-status=dead }}</ref> The same research made it very clear that it is safer for cyclists not to have priority over motor vehicles on the roundabout, than to have it.<ref name=Windesheim/> At least 70 have been built in the Netherlands, while many turbos (or similar, lane splitting designs) can be found in southeast Asia.<ref>{{cite web
|url=http://www.kuleuven.be/traffic/stats/download.php?id=21 |title=Capacity of a turbo-roundabout determined by micro-simulation |author1=Isaak Yperman |author2=Ben Immers |year=2003 |work=Katholieke Universiteit Leuven, Department of Civil Engineering – Transportation Planning and Highway Engineering
| format=pdf |archive-url=https://web.archive.org/web/20161227193135/http://www.kuleuven.be/traffic/stats/download.php?id=21 |archive-date=27 December 2016}} [http://www.kuleuven.ac.be/traffic/dwn/P2003D.pdf Alt URL]</ref> The turbo roundabout design is given as an example<ref>{{cite web |url=https://mutcd.fhwa.dot.gov/pdfs/2003r1r2/ch3.pdf |title=Manual on Uniform Traffic Control Devices for Streets and Highways – Part 3: Markings |year=2003 |work=U.S. Department of Transportation – Federal Highway Administration }}</ref> in the federal [[Manual on Uniform Traffic Control Devices]].

===Sub-sea roundabouts===
A new development is the roundabout below the seabed, in locations where multiple undersea traffic tunnels join. The first such roundabout is in the Eysturoy Tunnel ([[Eysturoyartunnilin]]), opened in December 2020 in the [[Faroe Islands]]. It connects the main island [[Streymoy]] with two locations on the island [[Eysturoy]] that are separated by a long fjord, [[Skálafjørður]]. So, three roads meet at this roundabout. Total length of the system is 11.24 km (6.98 mi). It was the largest ever infrastructure project in the Faroe Islands, estimated to have cost around a billion Danish kroner.<ref>For sources and references see the [[Eysturoyartunnilin|separate article]] on this tunnel and its roundabout.</ref>

=== Motorways ===
{{See also|Roundabout interchange}}
[[File:Opatovice nad Labem kruhový objezd from air K2 -1.jpg|thumb|Motorway junction with roundabout near [[Opatovice nad Labem]], Czech Republic]]

Roundabouts are generally not appropriate for placement on motorway or freeway mainlines because the purpose of such facilities is to provide for uninterrupted traffic flow. However, roundabouts are often used for the junction between the slip roads (called ''ramps'' in North America) and the intersecting road. A single roundabout, [[grade separation|grade separated]] from the mainlines, may be used to create a [[roundabout interchange]]. This type of junction is common in the UK and Ireland.

Alternatively, separate roundabouts also may be used at the slip road intersections of a [[diamond interchange]] to create what often is referred to as a "[[dumbbell interchange]]", which is increasingly common in both Europe and [[North America]] due to its reduced need for wide or multiple bridges. A variation of the dumbbell interchange, often called a "[[dogbone interchange]]", occurs when the roundabouts do not form a complete circle but are instead raindrop roundabouts (described [[#Raindrop roundabouts|above]]). This configuration reduces conflicts between vehicles entering the raindrop roundabouts from the ramps, reducing queueing and delays, compared with the dumbbell interchange.

Additional use of roundabouts for high-speed junctions is the [[roundabout interchange#Three-level stacked roundabout|3-level stacked roundabout]]—this is a [[roundabout interchange]] where ''both'' of the roadway mainlines are grade separated. In the United Kingdom, the [[M25 motorway|M25]]/[[A3 road|A3]], [[M8 motorway (Great Britain)|M8]]/[[M73 motorway|M73]] and [[A1 road (Great Britain)|A1(M)]]/[[M18 motorway (Great Britain)|M18]] interchanges are examples of this type. These junctions, however, have less capacity than a full [[free-flow interchange]]. A similar design to this is the [[three-level diamond interchange]].

Most junctions on [[Dublin]]'s M50 motorway C-road were built using a standard roundabout interchange. The traffic volume of several of these junctions increased to a level higher than the capacity such roundabouts can accommodate, and in turn, have been converted into partially or fully free-flowing interchanges. One example is the [[Red Cow interchange]]. In [[Northern Ireland]], the junction between the [[M1 motorway (Northern Ireland)|M1]] and [[M12 motorway|M12]] (Craigavon connector motorway) is via a standard roundabout with a raised centre, three onslips and three offslips, and two lanes.

In the city of [[Malmö]], Sweden, a roundabout connects two motorways, E22 from [[Lund]], and the [[Inre Ringvägen|Inner ring road]].

In the Netherlands, [[A6 motorway (Netherlands)|A6 motorway]] and [[A7 motorway (Netherlands)|A7 motorway]] used to cross near [[Joure]] using a roundabout until October 2017, when the junction was turned into a full [[Interchange (road)#Directional T interchange (Y-interchange)|Y-interchange]].<ref>{{Cite web|url=https://www.lc.nl/friesland/Video-Eerste-rit-over-het-nieuwe-knooppunt-Joure-22575041.html|title=Video: Eerste rit over het nieuwe knooppunt Joure|website=Leeuwarder Courant|date=13 October 2017 }}</ref> The junction between the [[A200 motorway (Netherlands)|A200]] and the [[A9 motorway (Netherlands)|A9]] uses a 3-level stacked roundabout. Near [[Eindhoven]] (the Leenderheide junction), the junction for the [[A2 motorway (Netherlands)|A2]] uses a roundabout. An overpass was built for the [[A67 motorway (Netherlands)|A67]] from Antwerp to Germany.

Near [[Liège]], Belgium, the Cheratte interchange between the [[A3 motorway (Belgium)|A3/E40]] and [[A25 road (Belgium)|A25/E25]] functions partially as a roundabout, with through traffic allowed to continue without entering the junction and traffic changing between motorways required to use the roundabout.

Rotary interchanges operate with [[traffic circle]]s rather than roundabouts. Rotary interchanges are common in [[New England]], particularly in the state of [[Massachusetts]], but a European example of a rotary interchange may be found in [[Hinwil]], Switzerland.

=== Signalised roundabouts ===
[[File:Old Market Roundabout, Bristol.jpg|thumb|A major signal-controlled roundabout interchange in central [[Bristol]], England. Vehicles drive on the left, and vehicles in the roundabout are stopped by traffic lights to allow other vehicles to enter, while an [[underpass]] permits straight-through traffic to bypass the roundabout entirely.]]

A signalised roundabout is one where one or more entry is controlled by traffic signals, rather than by assumed priority. For each signalised entry there will also be a signalised stopline immediately upstream on the circulatory section. The signals prevent blocking on the roundabout, and balance and improve traffic capacity.<ref>UK Department for Transport, Signal Controlled Roundabouts LTN 1/09</ref>

Examples include the M50 in Dublin; the Cherry Street roundabout in [[Kowloon]], Hong Kong; Sheriffhall Roundabout in Edinburgh, Scotland; Newton Circus in [[Singapore]]; and many of the roundabouts along the [[Paseo de la Reforma]] in [[Mexico City]].

An evolution of the signalised roundabout has been proposed recently.<ref>{{cite journal |last1=Ibanez |first1=Guillermo |title=Synchronous Roundabouts with Rotating Priority Sectors (SYROPS): High Capacity and Safety for Conventional and Autonomous Vehicles |journal=Electronics |date=2020 |volume=9 |issue=10 |page=1726 |doi=10.3390/electronics9101726 |doi-access=free |hdl=10017/44928 |hdl-access=free }}</ref> It is based in avoiding stops by eliminating conflict points in roundabouts. This proposed new paradigm (SYROPS) forms platoons of vehicles (e.g. 2 x 3 cars) that arrive at the roundabout with speed identical to the average circulation speed in the roundabout and within the time interval (visualised as a rotating priority sector) assigned to his entrance, avoiding all the conflicts of passage and with it the stops and accelerations required in standard and in signalled roundabouts. Signalling signage is with lights for human drivers and optionally wireless for connected and autonomous vehicles.{{undue weight inline|date=October 2022}}

=== "Magic" roundabouts/ring junctions ===
{{anchor|"Magic" roundabouts|Magic roundabout|ring junction}}
"Magic roundabouts" direct traffic in both directions around the central island. They are officially known as "ring junctions". The [[Magic Roundabout (Swindon)|first magic roundabout]] was constructed in 1972 in [[Swindon]], Wiltshire, United Kingdom, designed by [[Frank Blackmore]],<ref name="timesonline1">{{cite news |title=Frank Blackmore: traffic engineer and inventor of the mini-roundabout |url=http://www.timesonline.co.uk/tol/comment/obituaries/article4131930.ece |archive-url=https://web.archive.org/web/20100524152615/http://www.timesonline.co.uk/tol/comment/obituaries/article4131930.ece |url-status=dead |archive-date=24 May 2010 |work=The Times |date=14 June 2008 |access-date=15 June 2008 |location=London}}</ref> inventor of the mini-roundabout. The roundabout joins five roads and consists of a two-way road around the central island, with five mini-roundabouts meeting the incoming roads.<ref>{{Citation |title=Swindon's Magic Roundabout from the air |url=https://www.youtube.com/watch?v=Kafx_GGHqVg |language=en |access-date=23 March 2022}}</ref>

The name derives from the popular children's television series, ''[[The Magic Roundabout]]'', and is considered "magic" because traffic flows in both clockwise and anticlockwise directions. This is achieved by surrounding the main island with one smaller roundabout per entry/exit street. This pattern directs traffic in the usual clockwise (in [[Left- and right-hand traffic|LHT]] installations) or counter-clockwise (in [[Left- and right-hand traffic|RHT]] installations) manner around each mini-roundabout. Exiting the mini-roundabouts, traffic may proceed around the central island either in the usual direction (via the outer loop), or in the inverse direction (the inner loop). The arrangement offers multiple paths between feeder roads. Drivers typically choose the shorter, most fluid route. Although the safety record is good,{{cn|date=September 2024}} many drivers find this system intimidating, and some drivers go to great lengths to avoid them.<ref>[http://www.easier.com/view/News/Motoring/article-33515.html Brits vote on the best and worst roundabouts], Easier.com. 20 December 2005, retrieved 18 January 2008</ref><ref>{{Cite web|url=https://www.autoexpress.co.uk/car-news/29798/world-s-worst-junctions|title=World's worst junctions revealed|website=Auto Express}}</ref><ref>[http://news.bbc.co.uk/1/hi/england/london/7140892.stm 10 Scariest Junctions in the UK], BBC, 27 November 2009.</ref>

Similar systems are found in the [[Magic Roundabout (Hemel Hempstead)|Moor End roundabout]] in [[Hemel Hempstead]] (Hertfordshire), which has six intersections; in [[Magic Roundabout (High Wycombe)|High Wycombe]] (Buckinghamshire),<ref>{{google maps|url=https://www.google.co.uk/maps/@51.6268496,-0.7505916,18.67z|title=High Wycombe}}</ref> the [[Denham Roundabout]] in [[Denham, Buckinghamshire|Denham]] (Buckinghamshire), the [[Magic Roundabout (Colchester)|Greenstead Roundabout]] in [[Colchester]] (Essex), "[[The Egg (roundabout)|The Egg]]" in [[Tamworth, Staffordshire#The Egg Roundabout|Tamworth]] (Staffordshire) and the [[Hatton Cross]] Roundabout in London.<ref>{{google maps|url=http://maps.google.co.uk/maps?ll=51.467877,-0.423285&spn=0.003068,0.00392 |title=Hatton Cross}}</ref>

[[Churchbridge Junction]] in [[Staffordshire]] is a magic gyratory. This type of junction is similar to a magic roundabout, except that the constituent roundabouts are connected by longer lengths of roadway.<ref name="sabre_magic">{{cite web|title=SABRE: Magic Gyratory|url=http://www.sabre-roads.org.uk/wiki/index.php?title=Magic_Gyratory|access-date=8 November 2013|date=8 November 2013}}</ref>

<gallery widths="200px" heights="150px" class="center">
Magic Roundabout Schild db.jpg|The [[Magic Roundabout (Swindon)|Swindon Magic Roundabout]]
Swindon_magic_roundabout.svg|Map with traffic direction and two routes from Fleming Way to Queen's Drive
</gallery>

=== Dutch-style roundabouts for bicycles and pedestrians ===
{{see also|Protected intersection#Protected roundabouts}}
[[File:Alternative_dutch_roundabout.png|thumb|Dutch-style roundabout]] [[File:Trams at Nationaltheatret.jpg|thumb|Near [[Nationaltheatret]] in [[Oslo]], [[tram]]ways cross the roundabout]]
[[File:Haymarket roundabout 018.JPG|thumb|[[Haymarket roundabout]], [[Melbourne]]]]

=== Trams ===
[[Tram]] roundabouts, which are found in many countries, combine roundabouts for individual vehicles with tram lines. Large areas are needed for tram roundabouts that include a junction between tram lines. Tramways usually cross the centre of the roundabout. At busy junctions, this requires traffic lights or special signalling granting the trams priority. However, there are also roundabouts where trams and vehicles share the carriageway. Some roundabouts have a tram stop on the island.

*In France, tram roundabouts commonly have radii between 14 and 22 metres, although some have radii outside this range.<ref name="utp.fr">{{Cite web |url=https://www.utp.fr/sites/default/files/Dpt_AET/201706_Cerema-STRMTG_Giratoires_et_tramways.pdf |title=Archived copy |access-date=19 October 2019 |archive-url=https://web.archive.org/web/20191019114458/https://www.utp.fr/sites/default/files/Dpt_AET/201706_Cerema-STRMTG_Giratoires_et_tramways.pdf |archive-date=19 October 2019 |url-status=dead }}</ref>
*In some cities, the tramway bisects the roundabout. The French {{ill|Cerema|fr}} considers that the mix of priorities makes these confusing and difficult to understand: a traditional modern roundabout gives the priority to the central ring, while tram roundabouts give priority to the central ring but higher priority still to the tramway. This generates many collisions of cars and trams, between 7 and 10 for each tram roundabout in France between 2006 and 2015 (between 0.37 and 1.01 per year).<ref name="utp.fr" />{{contradictory-inline|reason=the per-year figures don't multiply up to the figures over 11 years|date=September 2020}}
*In inner [[Melbourne]], particularly in the inner suburban area of [[South Melbourne]], where the [[Trams in Melbourne|tram network]] is extensive, tram tracks always pass through the central island, with drivers required to give way to vehicles approaching from their right and to trams approaching from right angles. The [[Haymarket roundabout]] between [[Royal Parade, Melbourne|Royal Parade]] and [[Elizabeth Street, Melbourne|Elizabeth Street]] contains a tram-stop, pedestrian crossings, three entering tram lines, traffic signals to stop vehicular traffic at each crossing point when a tram is due, service roads and a pedestrian crossing.
*[[Brussels]] tram roundabouts employ multiple configurations. At the Barrière de [[Saint-Gilles, Belgium|St-Gilles]] (Dutch: {{lang|nl|Bareel St-Gillis}}), tram tracks form a circle in the carriageway, while Churchill, Verboekhoven and Altitude Cent (''Hoogte Honderd'') have reserved tram tracks inside the roundabout. At Vanderkindere and Place Stéphanie (''Stefaniaplein''), they go straight through the centre, in the latter case with a slip track up the Chaussée de Charleroi (''Charleroisesteenweg''), while at Montgomery they tunnel underneath.
*In Dublin, Ireland, the [[Red Cow interchange]] at the [[N7 road (Ireland)|N7]]/M50 junction is grade-separated and is signal-controlled with secondary lanes (separate from the main roundabout) for those making left turns. The junction, the busiest in Ireland, had tram lines added to it with the opening of the [[Luas]] system in 2004. The tracks pass across one carriageway of the N7, and across the southern M50 sliproads. Trams pass every five minutes at rush hour. The roundabout was replaced with a grade-separated free flowing junction.
*[[Gothenburg, Sweden]] has a tram roundabout at Mariaplan in the inner suburb of Majorna. The trams make a right turn, giving the roundabout an odd design.
*In [[Warsaw]], trams typically cross straight through roundabouts and have junctions in the centre of them. In [[Wrocław]], Poland, trams pass through the Powstańców Śląskich Roundabout, stopping in the roundabout (north-headed track).
*The [[Silesian Interurbans|Silesian tram network]] in Poland has two tram roundabouts. In the city centre of [[Katowice]], the tram line passes through the centre of the Ziętka Roundabout in a north–south alignment, with a tram stop in the centre of the circle.{{efn|There is also a branch line immediately north of the roundabout going west, and an additional tram stop on that branch.}} In [[Będzin]], unusually, the tram junction itself forms a circular roundabout, with trams going around the circle; there are tram stops immediately outside the roundabout on each branch.
*In Vítězné náměstí (Victory Square) in [[Prague]], Czech Republic, a tramway crosses the carriage way of the roundabout at three places. Entering as well as leaving trams give way to vehicles. In the years 1932–42 trams circulated much like vehicles.<ref>[http://www.prazsketramvaje.cz/view.php?cisloclanku=2006041435 Vítězné náměstí], Prague trams fun web</ref>
*In [[Kyiv]], Ukraine an interchange of two "[[Trams in Kyiv|fast tram]]" lines is below a roundabout.
*[[Oslo]], Norway also has many roundabouts with [[Oslo Tramway|tram]] tracks passing through; for example at Bislett, Frogner plass, [[Sinsen]], Solli plass, Carl Berners plass and Storo.
*In [[Wolverhampton, England]], the [[West Midlands Metro]] tram passes through the centre of a roundabout on the approach to its terminus at [[Wolverhampton St George's tram stop|St Georges]]. This also happens in [[New Addington]] in [[Croydon]] on the [[Tramlink]] north of [[King Henry's Drive tram stop]] on Old Lodge Lane at the junction to King Henry's Drive.
*In [[Sheffield, England]] the [[Sheffield Supertram]] systems crosses two major roundabouts. At the Brook Hill roundabout near [[University of Sheffield|Sheffield University]], the tramway passes underneath the roundabout in a subway, while at Park Square in the city centre it travels above the roundabout on bridges and viaducts with a junction in the central island.
*A roundabout in southern [[Zagreb]], Croatia features tram tracks passing through, curving at a 90° angle, as well as a full tram mini-roundabout inside the middle road island. In Croatia, where tram tracks enter the road without traffic lights, trams have the highest priority and other non-emergency vehicles are required to yield.
*In [[Salt Lake City, Utah]] a [[light rail]] line on the south side of the [[University of Utah]] crosses a roundabout where Guardsman Way meets South Campus Drive. Like virtually all rail crossings in the United States, both crossings in the circle are equipped with [[boom barrier]]s.
*In [[Kassel]], Germany, Lines 4 and 8 pass through the centre of the roundabout at Platz der Deutschen Einheit. The tram stops are in the centre of the roundabout. Roundabout traffic is controlled by traffic lights. Pedestrian access is via subway and street-level crossings at the lights.
*In [[Bremen]], Germany, tram lines 8 and 6 pass through the centre of the roundabout "Am Stern" east of the main railway station. They enter from the west and exit in a northeastern direction, thus making a slight bend within the roundabout. Both stations are situated on the north-eastern edge of the roundabout. Traffic is controlled by two-colour traffic lights inside the roundabout.

=== Railways ===
[[File:Blenheim Main Street Roundabout looking north (LCM20210404).jpg|thumb|The [[Main North Line, New Zealand|Main North Line]] railway bisects the {{NZlSH|1}}/Main Street roundabout in [[Blenheim, New Zealand|Blenheim]], New Zealand.]]
In [[Jensen Beach, Florida]], the main line of the [[Florida East Coast Railway]] running north–south bisects the two-lane roundabout at the junction of Jensen Beach Boulevard running east–west. It hosts three other roads and the service entrance to a large shopping plaza. Boom barriers line the railway crossings. The landscaped central island bisected by the tracks was originally [[kerb]]ed, but [[semi-trailer truck|18-wheelers]] had trouble negotiating the roundabout, so the kerbs were replaced with painted concrete strips. The roundabout was built in the early 2000s and improved traffic flow, although long freight trains often cause delays.<ref>{{google maps |url= http://maps.google.co.uk/maps?hl=en&q=27.24395,+-80.22742&safe=active&um=1&ie=UTF-8&hq=&hnear=0x88dee7066d9fab49:0xd4730553b50a5cbf,%2B27%C2%B0+14'+38.63%22,+-80%C2%B0+13'+38.60%22&gl=uk&ei=aIUNTszzGMqphAe-5NXfDQ&sa=X&oi=geocode_result&ct=image&resnum=1&ved=0CBkQ8gEwAA |title Jensen Beach Boulevard Roundabout |access-date= 15 January 2012}}</ref><ref>{{cite web|url=http://www.tcrpc.org/departments/studio/jensen_beach_downtown_charrette/roundabouts/roundabouts_home.htm|title=Jensen Beach Roundabouts Charrette|access-date=16 October 2007|archive-date=21 November 2008|archive-url=https://web.archive.org/web/20081121070652/http://www.tcrpc.org/departments/studio/jensen_beach_downtown_charrette/roundabouts/roundabouts_home.htm|url-status=dead}}</ref>

Two roundabouts in the Melbourne metropolitan area, [[Highett, Victoria]]<ref>{{cite web|url=http://www.street-directory.com.au/aust_new/index.cgi?CountryName=vic&x=145.039044269836&y=-37.9447586507931&level=6|work=Australia Mapsearch|title=145.039044269836,-37.9447586507931}}</ref> and [[Hampton, Victoria|Hampton]],<ref>{{cite web|url=http://www.street-directory.com.au/aust_new/index.cgi?CountryName=vic&x=144.9930580000&y=-37.9200150000&level=6|work=Australia Mapsearch|title=144.9930580000&,-37.9200150000}}</ref> have [[passenger rail terminology#Heavy rail|heavy rail]] crossing the roundabout and through the inner circle. Boom barriers protect the railway from oncoming traffic at the appropriate points in the roundabout.

At the Driescher Kreisel<ref>{{Cite web|url=http://www.bergischgladbach.de/driescher-kreisel-1.aspx|archiveurl=https://web.archive.org/web/20110927063931/http://www.bergischgladbach.de/driescher-kreisel-1.aspx|url-status=dead|title=Der Driescher Kreisel|archivedate=27 September 2011}}</ref> in [[Bergisch Gladbach]], Germany, a railway serving a nearby paper factory crosses a roundabout located next to a shopping centre and pedestrian zone. The flow of traffic and pedestrians is governed by 14 barriers, 22 traffic lights and 8 loudspeakers. The barriers close three times daily for 7 minutes to allow trains to pass.

In New Zealand's [[South Island]], two roundabouts join major roads where a railway cuts through. One is at the intersection between {{NZlSH|1}} (as Sinclair Street and Main Street from the east) and Main Street (from the west), Park Terrace and Redwood Street in the city of [[Blenheim, New Zealand|Blenheim]]. Here the [[Main North Line, New Zealand|Main North Line]] bisects the roundabout and separates Park Terrace and Main Street eastbound from the rest of the roundabout.<ref>{{google maps |title= Blenheim Roundabout |url=https://maps.google.com.au/maps?q=-41.51345+173.95987&hl=en&sll=-41.513261,173.960298&sspn=0.004362,0.010568&vpsrc=0&t=h&z=16 |access-date= 15 January 2012}}</ref> The other roundabout is located at [[Kumara Junction]] on the [[West Coast, New Zealand|West Coast]], where the [[Hokitika Branch]] separates {{NZlSH|6}} southbound from SH 6 northbound and {{NZlSH|73}}.<ref>{{google maps |title= Kumara Junction Roundabout |url= https://maps.google.com.au/maps?q=-42.58515%09171.12974&hl=en&ll=-42.585247,171.129779&spn=0.002145,0.005284&sll=-42.585184,171.129549&sspn=0.004289,0.010568&vpsrc=6&t=h&z=18 |access-date=15 January 2012}}</ref> Both roundabouts are controlled by flashing red lights, with additional boom barriers at the Blenheim roundabout.

=== Through roundabout ===
{{anchor|Hamburger roundabout}}
Also known as a hamburger roundabout, these junctions are [[traffic light|signalised]] and have a straight-through section of carriageway for one of the major routes. The ''hamburger'' name derives from the fact that the [[plan view]] resembles the cross-section through a [[hamburger]]. The United Kingdom has examples on the [[A580 road|A580 East Lancashire Road]] in [[St Helens, Merseyside|St Helens]], on [[Haydock|Haydock Island]] in Merseyside<ref>{{google maps|url=http://local.google.co.uk/?ie=UTF8&ll=53.470883,-2.63556&spn=0.005965,0.020127&om=1|title=Haydock Island in Merseyside}}</ref> (which also features the M6 passing overhead), and on the Astley/Boothstown border.<ref>{{google maps|url=http://local.google.co.uk/?ie=UTF8&om=1&ll=53.505086,-2.431648&spn=0.00596,0.020127 Astley/Boothstown border}}</ref> More examples are the [[A6003 road|A6003]] at [[Kettering]], the [[A538 road|A538]] near [[Manchester Airport]], the "Showcase" junction on A329 at Winnersh, Berkshire<ref>{{google maps|url=https://www.google.co.uk/maps/@51.4362134,-0.8977845,267m/data=!3m1!1e3?hl=en |title=Winnersh, Berkshire}}</ref> and the A63/A1079 Mytongate junction in Hull. Examples also exist in [[Bracknell]], Hull,<ref>{{google maps|url=http://maps.google.co.uk/maps?q=hull&ie=UTF8&oe=utf-8&client=firefox-a&ll=53.740472,-0.343572&spn=0.001618,0.004828&t=h&z=18 |title=Mytongate on the A63 in Hull}}</ref> Bramcote in Nottinghamshire and [[Reading, Berkshire|Reading]], as well as on the [[N2 road (Ireland)|N2]]/[[M50 motorway (Ireland)|M50]] intersection in [[Dublin]], Ireland. In [[Perth]], Western Australia, one is found at the intersection of [[Alexander Drive]], [[Morley Drive]] and The Strand.<ref>{{google maps|url=https://maps.google.com.au/maps?q=Morley+Drive+and+Alexander+Drive&hl=en&ll=-31.889692,115.87218&spn=0.006532,0.013078&sll=-31.884409,115.872562&sspn=0.10451,0.209255&t=h&hnear=Alexander+Dr+Before+Morley+Dr&z= |title=Morley and Alexander Drive}}</ref> Throughabouts are very common in Spain, where they are called ''raquetas'' (Spanish for [[racket (sports equipment)|{{nowrap|"[tennis]}} racket"]]) or ''glorieta/rotonda partida'' ("split roundabout").<ref>{{cite web | url = http://autoescuelamiguel.com/blog/2010/cmo-circular-en-una-glorieta-partida-raqueta/ | website = Autoescuela Miguel Blog | title = Cómo circular en una Glorieta Partida (raqueta) | access-date = 17 October 2014 | language = es | quote = Explanation in the website of a driving school | archive-date = 17 October 2014 | archive-url = https://web.archive.org/web/20141017113216/http://autoescuelamiguel.com/blog/2010/cmo-circular-en-una-glorieta-partida-raqueta/ | url-status = dead }}</ref>

<gallery widths="200px" heights="200px" class="center">
Throughabout.svg|Throughabout
Throughabout Rotonde Verkeersbord 3.jpg|Throughabout road sign in the Netherlands {{coord|51.850517|N|5.831576|E}}
E37 AlexanderDr-MorleyDr sign.jpg|Throughabout road sign in Australia {{coord|31.8902952|S|115.8698988|E}}
</gallery>

==== Only bicycle-pedestrian roundabouts ====
The same features that make roundabouts attractive for roadway junctions led to their use at junctions of multi-use trails.

The [[University of California, Davis]]<ref>{{google maps|url=https://maps.google.com/maps?f=q&source=s_q&hl=en&geocode=&q=university+of+california+davis,+CA+roundabout&sll=33.709367,-117.770775&sspn=0.012513,0.018604&g=davis,+CA+roundabout&ie=UTF8&ll=38.54252,-121.753364&spn=0.001471,0.003345&t=k&z=19 |title=Davis, Ca.}}</ref>{{Original research inline|date=May 2020}} and [[Stanford University]], as well as the [[Cape Cod Rail Trail|Cape Cod]] and [[Old Colony Rail Trail|Old Colony]] rail trails have bicycle-pedestrian roundabouts. A roundabout along the [[Clear Creek Trail (Indiana)|Clear Creek Trail]] in [[Bloomington, Indiana]], connects the main [[trail]] to its [[Trail#Linear|spur]].

Roundabouts are used on off-road bicycle trails in [[Florida]], [[Colorado]], [[Alaska]], and [[Wisconsin]].<ref>Shaw, Jeffrey and Moler, Steve, [http://www.tfhrc.gov/pubrds/09janfeb/01.htm Bicyclist- and Pedestrian-Only Roundabouts, Public Roads magazine, January/February 2009] {{Webarchive|url=https://web.archive.org/web/20090510100804/http://www.tfhrc.gov/pubrds/09janfeb/01.htm |date=10 May 2009 }}</ref><ref>{{cite web|url=http://www.tfhrc.gov/safety/00068.htm|title=Federal Highway Administration Research and Technology-- – Federal Highway Administration|access-date=5 September 2006|archive-url=https://web.archive.org/web/20060923055232/http://www.tfhrc.gov/safety/00068.htm|archive-date=23 September 2006|url-status=dead}}</ref><ref>{{cite news|url=http://host.madison.com/ct/news/local/photos-bicycle-roundabout-sits-at-intersection-of-bike-paths/collection_0ae6d40a-3916-11e4-8e0d-0019bb2963f4.html|title=Bicycle roundabout sits at intersection of 3 bike paths|work=The Capital Times}}</ref>

An elevated roundabout is located in [[Eindhoven]], serving pedestrian and bicycle traffic only, above the main conventional roadway intersection. It is known as the [[Hovenring]].

== See also ==
{{For|the at-grade intersection design analogous to dumbbell and dogbone interchanges|Bowtie (road)}}
{{div col|colwidth=30em}}
* [[Complete streets]]
* [[Direction of traffic]]
* [[History of road transport]]
* [[History of street lighting in the United States]]
* [[History of roads in Ireland]]
* [[Level of service (transportation)|Level of service]]
* [[Leif Ourston]], an early proponent of roundabouts in the United States
* [[Roundabout Appreciation Society]]
* [[Roundabout dog]]
* [[Traffic congestion]]
{{div col end}}

== Notes ==
{{Notelist}}

==References==
{{Reflist}}

== Sources ==
* {{cite web|url=https://www.fhwa.dot.gov/publications/research/safety/00067/000671.pdf |last=U.S. Department of Transportation |title=Roundabouts: an Informational Guide |year=2013}}
* {{cite news |last1=Stenquist |first1=Paul |title=All About Roundabouts |url=https://www.nytimes.com/2020/08/20/business/roundabouts-traffic-circles.html?action=click&algo=bandit-story&block=more_in_recirc&fellback=false&imp_id=136806424&impression_id=89b41000-e5b2-11ea-87a3-530a1d44e7aa&index=0&pgtype=Article&region=footer&req_id=772645184&surface=more-in-business |access-date=29 August 2020 |work=The New York Times |date=20 August 2020}}

== External links ==
{{Commons category|Roundabouts}}
* [https://www.carmel.in.gov/government/departments-services/engineering/roundabouts City of Carmel, Indiana, USA, Roundabouts page]
* [https://carfreeamerica.net/roundabout-guide/ Car Free America Roundabout Safety and Design Guide]
* [https://www.youtube.com/watch?v=ZyZXtURfufo Video of Highway Roundabout in Canada]
* [http://www.trl.co.uk/ TRL, The UK's Transport research Laboratory]
* [http://roundabouts.kittelson.com/ Modern Roundabouts] – Geocoded National Database
* [http://www.mini-roundabout.com/details.html Mini-roundabouts – Getting them Right]
* [https://web.archive.org/web/20120425233810/http://www.brennerplan.de/downloads_manuell/turbokreisel.wmv Turbo Roundabout Simulation]
* [http://www.wsdot.wa.gov/Safety/roundabouts/benefits.htm Roundabout Benefits] from the Washington State Department of Transportation
* [http://www.mto.gov.on.ca/english/engineering/roundabout/index.shtml Highway Roundabouts] from the Ministry of Transportation of Ontario
* [https://web.archive.org/web/20130328102033/http://roundaboutsnow.com/roundabouts Roundabouts Now]
* [http://www.turboroundabout.com/benefits.html Benefits of a Turboroundabout]
*[http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_syn_264.pdf Modern Roundabout Practice in the United States] from Transportation Research Board
* [http://teachamerica.com/ Proceedings from the Transportation Research Board Standing Committee on Roundabouts (ANB75)]

{{Road junction types}}
{{Authority control}}

[[Category:Roundabouts and traffic circles| ]]
[[Category:Road junction types]]
[[Category:French inventions]]