# Hairpin turn

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{{short description|Acute curve (often one of a series) in a road, especially on a steep incline}}
{{more citations needed|date=July 2014}}
thumb|Hairpin turn in Oregon, US
thumb|A hairpin, after which the feature is named

A '''hairpin turn''' (also '''hairpin bend''' or '''hairpin corner''') is a bend in a road with a very acute inner angle, making it necessary for an oncoming vehicle to turn about 180° to continue on the road. It is named for its resemblance to a bent metal [hairpin](/source/bobby_pin). Such turns in ramps and [trail](/source/trail)s may be called '''switchbacks''' in [American English](/source/American_English) by analogy with [switchback railways](/source/Zig_Zag_(railway)).

== Description ==
Hairpin turns are often built when a route climbs up or down a steep slope, so that it can travel mostly across the slope with only moderate steepness, and are often arrayed in a zigzag pattern. [Highways](/source/Highways) with repeating hairpin turns allow easier and safer ascents and descents of mountainous terrain than does a direct and steep climb and descent at the price of greater distances of travel and usually lower [speed limits](/source/speed_limits) because of the sharpness of the turn. Highways of this style are also generally less costly to build and maintain than highways with [tunnels](/source/tunnels).

On occasion, the road may loop completely, using a tunnel or bridge to cross itself at a different elevation (on [Reunion Island](/source/Reunion_Island), {{coord|21|10|52|S|55|27|17|E}}, and near [Ashland, Oregon](/source/Ashland%2C_Oregon), {{coord|42|05|31|N|122|35|21|W}}). When this routing geometry is used for a rail line, it is called a [spiral](/source/spiral_(railway)) or a spiral loop.

In building [trails](/source/Trail), an alternative to switchbacks is the [stairway](/source/stairway).

==Notable hairpin turns==
thumb|Looking into the Fairmont Hairpin
* [Clarks Summit, Pennsylvania](/source/Clarks_Summit%2C_Pennsylvania) at the north end of [Interstate 476](/source/Interstate_476) (eases the grade for trucks)
* {{Annotated link |Devil's Elbow, Isle of Man}}
* {{Annotated link |Governor's Bridge (Isle of Man)}}
* {{Annotated link |Ramsey Hairpin}}
* Fairmont Hairpin – hairpin bend at the [Fairmont Monte Carlo](/source/Fairmont_Monte_Carlo) on the [Circuit de Monaco](/source/Circuit_de_Monaco)
* Sitinjau Lauik - hairpin bend at the [Padang City](/source/Padang_City) and [Solok](/source/Solok) road. Part of national road and Sumatra highway
* [Trollstigen](/source/Trollstigen)

== Railways ==
If a railway curves back on itself like a hairpin turn, it is called a [horseshoe curve](/source/horseshoe_curve). The [Pennsylvania Railroad](/source/Pennsylvania_Railroad) [built one](/source/Horseshoe_Curve_(Pennsylvania)) in [Blair County, Pennsylvania](/source/Blair_County%2C_Pennsylvania), which ascends the [Eastern Continental Divide](/source/Eastern_Continental_Divide) from the east. However, the [radius of curvature](/source/Track_transition_curve) is much larger than that of a typical road hairpin. See this example at Zlatoust<ref>{{cite web |url=https://maps.google.com/maps?f=q&source=s_q&hl=en&geocode=&q=%D0%97%D0%BB%D0%B0%D1%82%D0%BE%D1%83%D1%81%D1%82&sll=-21.184787,55.451244&sspn=0.002736,0.004823&ie=UTF8&hq=&hnear=Russian+Federation,+Province+of+Chelyabinsk,+Zlatoust&ll=55.085123,59.985309&spn=0.013436,0.038581&t=h&z=15 |title=Златоуст - Google Maps |work=google.com}}</ref> or [Hillclimbing](/source/Hillclimbing_(railway)) for other railway ascent methods.

== Skiing ==
Sections known as hairpins are also found in the [slalom](/source/slalom_skiing) discipline of [alpine skiing](/source/alpine_skiing). A hairpin consists of two consecutive vertical or "closed gates", which must be negotiated very quickly. Three or more consecutive closed gates are known as a [flush](/source/Slalom_skiing).<ref>{{cite magazine |url=https://books.google.com/books?id=M3N0Tsph6FwC&pg=PA35 |magazine=[Ski](/source/Ski_(magazine)) |title=Rating Gates, Coping With Injury |year=1985 |page=28}}</ref>

== See also ==
* [Dead Man's Curve](/source/Dead_Man's_Curve)
* [Spiral bridge](/source/Spiral_bridge)
* [Zig zag (railway)](/source/Zig_zag_(railway))
* [U-turn](/source/U-turn)

== References ==
{{reflist|30em}}

== External links ==
{{commons-inline|Category:Hairpin turns|Hairpin turns}}

{{Road types}}

Category:Motorsport terminology
Category:Road transport
Category:Road hazards

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Adapted from the Wikipedia article [Hairpin turn](https://en.wikipedia.org/wiki/Hairpin_turn) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Hairpin_turn?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.