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Road D2204 ascends to the Col de Braus using hairpin bends in the Alpes Maritimes in the French Alps ( 43°41′58″N, 7°22′50″E)

The kind of hair pin (bobby pin) from which a hairpin turn gets its name

Some of the 48 hairpin turns near the top of the northern ramp of the Stelvio Pass in Italy.

Hairpin turn on the Mont Ventoux in France

One of the most famous NASCAR tracks with hairpin turns was the old Riverside International Raceway in Riverside, California.

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: 21°10′52″S, 55°27′17″E).

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

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 Alpine Mountain passes
• 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 hardest challenge, 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

USA:

• Winters Street (Sacramento, CA)
• Lombard Street (San Francisco)
• Coronado Trail Scenic Byway (U.S. Route 191 in Arizona between Morenci and Alpine), has a few switchbacks and about 460 curves.^[1]
• Beartooth Highway in Montana and Wyoming
• U.S. Highway 93 on the Arizona side of Hoover Dam
• State Route 89A as it enters Oak Creek Canyon in Arizona
• State Route 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
• 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.
• Blue Ridge Parkway in North Carolina and Virginia
• Cherohala Skyway in Tennessee and North Carolina
• U.S. Highway 441 through Great Smoky Mountains National Park on the Tennessee/North Carolina border.
• Pali Highway, Hawaii, connecting Windward Oahu with Honolulu/Leeward Oahu
• Highway 7 in various places in Arkansas
• U.S. Highway 129 around the Tennessee/North Carolina border, 318 curves in 11 miles
• Massachusetts Route 2 in the Berkshire Mountains
• U.S. Route 44/NY 55/ in Ulster County, New York
• Washington State Route 410 between Cayuse Pass and Chinook Pass in Mount Rainier National Park, eastern Pierce County
• Washington State Route 20 just east of Washington Pass in Okanogan County

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 Tochigi Perfecture
• In Macau, a part of the Guia Circuit is a hairpin turn.

Australia:

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

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.

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.

1. ^ Coronado Trail, Arizona, Driving Tour @ National Geographic Traveler