Hairpin turn

A hairpin turn (also hairpin bend, hairpin corner, etc.), named for its resemblance to a hairpin/bobby pin, is a bend in a road with a very acute inner angle, making it necessary for an oncoming vehicle to turn almost 180º to continue on the road. Such turns in ramps and trails may be called switchbacks in American English, by analogy with switchback railways. In British English 'switchback' is more likely to refer to a heavily undulating road—a use extended from the rollercoaster and the "other" type of switchback railway.

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 with repeating hairpin turns allow easier, safer ascents and descents of mountainous terrain than a direct, steep climb and descent, at the price of greater distances of travel. Highways of this style are also generally less costly to build and maintain than highways with tunnels.

On occasion, the road may loop completely, using a tunnel or bridge to cross itself (example on Reunion Island: coord|21|10|52|S|55|27|17|E).

In trail building, an alternative to switchbacks is the stairway.

Roads with hairpin turns

Some roads with switchbacks (hairpin turns) include:

Europe

* Alpe d'Huez in the French Alps, famous for its 21 hairpin bends
* Stelvio Pass with its 48 "Spitzkehren" on the northern ramp is one of the most famous
* In rallying, the cars slide sideways around hairpins in spectacular style, e.g. at the Col de Turini of the Rallye Automobile Monte Carlo
* Hillclimbing is a special kind of automobile racing mainly held of mountains roads with hairpins, which keeps average speeds lower than on tracks
* In bicycle racing, climbs up mountains roads with many U-turns are considered the most difficult, and often feature in Tour de France, Giro d'Italia, Tour de Suisse and also Vuelta a España
* The roads above Monaco, on the foothills of the Alps; also seen in Hitchcock's "To Catch a Thief"
* The road up from Lysefjord is famous for its 27 hairpin bends
* The Trollstigen road from Åndalsnes to Valldal is famous for its 11 characteristic bends
* The Geiranger road from the famous Geirangerfjord to the mountain pass won the gold on the world exhibition, Paris 1900

USA

* City streets:
** Lombard Street (San Francisco)
** Winters Street (Sacramento, California)
* U.S. Highways:
** US 6 through Loveland Pass over the Continental Divide in Colorado.
** US 44/NY 55 in Ulster County, New York.
** US 93 on both the Nevada and Arizona sides of Hoover Dam, though these sections will be bypassed by a new highway alignment and bridge south of the dam, scheduled to open in 2010.
** US 129 around the Tennessee/North Carolina border, 318 curves in 11 miles.
** US 191 (Coronado Trail Scenic Byway) in Arizona between Morenci and Alpine), has a few switchbacks and about 460 curves. [ [http://www.nationalgeographic.com/traveler/deals/coronado.html?fs=plasma.nationalgeographic.com Coronado Trail, Arizona, Driving Tour @ National Geographic Traveler] ]
** US 441 through Great Smoky Mountains National Park on the Tennessee/North Carolina border.
* State Highways:
** AZ 89A as it enters Oak Creek Canyon in Arizona.
** AR 7 in various places in Arkansas
** CA 1 south of Bodega Bay, California; it is shown in Alfred Hitchcock's film "The Birds", is still in use, and looks much as it did during the filming in the early 1960s
** CA 198 on the ascent from the Kaweah River canyon to the Giant Forest area of Sequoia National Park. This portion of CA 198 is known as Generals Highway.
** MA 2 in the Berkshire Mountains
** WA 20 just east of Washington Pass in Okanogan County.
** WA 410 between Cayuse Pass and Chinook Pass in Mount Rainier National Park, eastern Pierce County.
* Other roads:
** Beartooth Highway in Montana and Wyoming
** Blue Ridge Parkway in North Carolina and Virginia
** Cherohala Skyway in Tennessee and North Carolina
** Pali Highway, Hawaii, connecting Windward Oahu with Honolulu/Leeward Oahu
** Though not a particularly tight one, New York's Taconic State Parkway has a hairpin turn in Putnam County, and is signed as an S-curve.
** Historic US 66 (Oatman Highway) between Kingman and Oatman, through Sitgreaves Pass in the Black Mountains, Arizona.

Americas

* Mexican Autopista 95D has a famous hairpin turn known as "La Pera" (The Pear), due to its loose resemblance with that fruit's shape.

Asia

* The World War II-era Burma Road, constructed over the rugged terrain between the (then) British colony of Burma and China has many hairpin curves to accommodate traffic to supply China, then otherwise isolated by sea and land.
* In Japan, there is the known Nikkō Irohazaka, a 1-way switchback mountain road (of course there are 2 separate roads; up and down), located at Nikko, Tochigi.
* In Macau, a part of the Guia Circuit is a hairpin turn.
* In India, the Gata Loops, a part of the route from Manali to Leh.

Australia

* The Mount Hotham Pass on the Great Alpine Road in Victoria has numerous hairpin bends, as do the other roads in the region.

Motorsports

Many venues used for motor racing incorporate hairpin turns in the racecourse even if the terrain is relatively level. In this case the purpose is to provide a greater challenge to the drivers or simply increase the lap length without increasing the area occupied by the track.

Railways

If a railway curves back on itself like a hairpin turn, it is called a Horseshoe curve. See Hillclimbing (railway) for other railway ascent methods.

kiing

Sections known as hairpins are also found in the slalom discipline of 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.)

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