Editing Roundabout (section)

=== 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]].