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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 about 180° 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 and usually lower speed limits, due to the sharpness of the turn. 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 at a different elevation (example on Reunion Island: ). When this routing geometry is used for a rail line, it is called a spiral, or spiral loop.
Some roads with switchbacks (hairpin turns) include:
- Alpe d'Huez in the French Alps, famous for its 21 hairpin bends
- Stelvio Pass (German: Stilfserjoch) with its 48 hairpin bends (Italian: tornanti; German Spitzkehren) on the northern ramp is one of the most famous Alpine Mountain passes
- Transfăgărăşan in the Romanian Carpathians (Fagaras Mountains), famous for its hairpin bends
- In rallying, the cars slide sideways around hairpins in spectacular style, such as at the Col de Turini of the Monte Carlo Rally
- Hillclimbing is a special kind of automobile racing mainly held of mountain 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 and the Loews Hairpin at the Circuit de Monaco
- The road between Lysefjord and the mountain plateau has 27 hairpin bends
- The Trollstigen road in Rauma, Norway, from Åndalsnes to Valldal has 11 characteristic bends. 
- The Geiranger road from Geirangerfjord to the mountain pass (now road 63) won the gold medal on the world exhibition, Paris 1900, the original design included a 270° spiral. 
- Norwegian National Road 7 through Måbødalen has a spiral partly within tunnels. 
- The road from Frangokastello to Kallikratis in Crete has 27 tight bends. Due to mountainous profile of the country are many public streets in Greece having tight bends, and the asphalt is little slippery, making the traction (and the control) easily loosen. The situation worsens with the first rains after the long dry summer, then asphalt slips more than usual
- The Veleta access road in Granada, Spain is the highest paved road in Europe
- City streets:
- US Highways:
- US 6 through Loveland Pass over the Continental Divide in Colorado (N39.65726, W105.87456)
- US 44/ NY 55 on the east face of the Shawangunk Ridge in Gardiner (N41.73803, W74.18433).
- US 93 used to be on both the Nevada and Arizona sides of Hoover Dam, though these sections were bypassed by a new highway alignment and bridge south of the dam that opened in 2010 (N36.01612, W114.73716)
- US 250 between the West Virginia border and West Augusta, Virginia (N38.44073, W79.63908)
- US 129 around the Tennessee/ North Carolina border, 318 curves in 11 miles (18 km) (N35.47612, W83.91830)
- US 191 (Coronado Trail Scenic Byway) in Arizona between Morenci and Alpine), has a few switchbacks and about 460 curves. (N33.16616, W109.36697)
- US 441 through Great Smoky Mountains National Park on the Tennessee/ North Carolina border. (N35.60273, W83.41527)
- US 40 over Berthoud Pass in Colorado. (N39.84474, W105.7578)
- US 550 in Colorado between Silverton and Ouray, nicknamed the "Million Dollar Highway" (N37.87297, W107.73610)
- US 34 in Colorado in Rocky Mountain National Park has 10 switchbacks on Trail Ridge Road
- 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 74/Seven-Level Hill south of Palm Desert, California, featured in the film It's a Mad, Mad, Mad, Mad World
- CA 92 southwest of the San Andreas Fault
- CA 120 west of Groveland, California is known as Priest Grade, a dangerous road on the way to Yosemite National Park.
- CA 130 Originally built as a wagon trail to aid in the construction of Lick Observatory, "Mt. Hamilton Road" travels east out of San Jose, CA and rises over the foothills, only to ascend again up the summit of Mt. Hamilton. It has a total of 365 curves and switchbacks: "...one for every day of the year"
- CA 152 east of Watsonville, California is known as Hwy 152 or Hecker Pass; from Casserly Rd to Whitehurst Rd it curves and makes a hairpin turn just past the "Mt. Madona Inn" Restaurant
- 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
- CO 5, the highest paved road in North America, has three switchbacks as it ascends from Echo Lake Park in Clear Creek County, Colorado, and an additional 12 switchbacks on its final approach to the summit of Mount Evans. It forms half of the Mount Evans Scenic Byway.
- CO 82 has one switchback on the western approach, and three on the east, at Independence Pass on the Lake– Pitkin county line, the highest paved crossing of the Continental Divide in the US
- MA 2, the Mohawk Trail in the Berkshire Mountains
- UT 261 includes steep switchbacks as it traverses the Moki Dugway in San Juan County
- 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
- NJ 495 just after leaving the Lincoln Tunnel toll plaza
- Other roads:
- Panoramic Highway in Marin County, California, includes dozens of hairpin turns as it traverses Mount Tamalpais, connecting the inland town of Mill Valley with the coastal community of Stinson Beach.
- Pikes Peak Highway in Colorado Springs includes numerous hairpins and switchbacks which are known as "W's". 
- Fairfax–Bolinas Road in Marin County, California, includes dozens of hairpin turns as it traverses the northern ridge of Mount Tamalpais, connecting the town of Fairfax in central Marin with the coastal community of Bolinas
- The Beartooth Highway in Montana and Wyoming has 19 switchbacks
- Blue Ridge Parkway in North Carolina and Virginia
- San Juan Grade Road in Salinas, California between Old Stage Rd and California Highway 156 in San Juan Bautista
- Cherohala Skyway in Tennessee and North Carolina
- W Road near Chattanooga, Tennessee, with 3 quick hairpin turns forming the letter "W"
- Pali Highway, Hawaii, connecting windward Oahu with Honolulu and leeward Oahu
- Taconic State Parkway in New York has a wide hairpin turn in Putnam County, which is signed as an S-curve
- Historic US 66 (Oatman Highway) between Kingman and Oatman, through Sitgreaves Pass in the Black Mountains, Arizona
- Palomar Mountain Road, also known as South Grade Road, in San Diego County has 21 switchbacks
- Greenwood Station Road ( US Bicycle Route 76) in Albemarle County, Virginia near Crozet with a signed "5 mph" hairpin turn. (N38.054588, W78.770537)
- Mexican Autopista 95D has a famous hairpin turn which is known as La Pera (The Pear), because it somewhat resembles the shape of that fruit.
- The Crowsnest Highway in British Columbia, Canada east of Osoyoos has several hairpin turns.
- A sharp hairpin turn on British Columbia Highway 97 alongside Vaseux Lake near Oliver, British Columbia has been the scene of many accidents and deaths.
- Nova Scotia Highway 105, part of the Trans-Canada Highway in Cape Breton has a hairpin turn after peaking Kelly's Mountain before descending to cross the Seal Island Bridge.
- The Duffy Lake Road (hwy 99) in British Columbia descending into Pemberton from Lillooet. 50°18'4.31"N, 122°35'4.50"W
- The Paso Internacional Los Libertadores has several switchbacks on the Chilean side of the pass. 26 below the tunnel entrance alone.
- 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 one-way switchback mountain road (there are 2 separate roads; up and down), located at Nikko, Tochigi. This road plays a significant role in Japanese history: The route was popular with Buddhist pilgrims on their way to Lake Chuzenji, which is at the top of the forested hill that this road climbs. There are 48 hairpin turns, each labeled with one of the 48 characters in the Japanese alphabet:   while the narrow road has been modernized over the years, care has been taken to keep the number of curves constant. Iroha-Zaka ascends more than 1,300 feet (396 m).[ citation needed]
- 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. And the Agumbe Ghat road from Udupi to Teerthahalli in Karnataka have 13 hairpin turns. In fact, most of the Ghats include at least one hairpin turn.
- In India, The Ghat road from Namakkal to Kolli Hills has 70 hair pin bends to reach the top of the hills.
- In China, Nujiang 72 turns/Baxoi 99 turns, part of China National Highway 318.
- In Iraq, the road going up the Sinjar mountains starting from Shangal town to Gune Ezidiya village of the Yazidi sect has between 90–100 hairpin turns over a distance of 20 km (12 mi) from starting point  to ending point. 
- In Philippines, Kennon Road on the way to/from Baguio has many hairpin turns. Also in Rizal, Cagayan, the road besides mountains and rivers have hairpin turns.
- In Nepal, B.P. Koirala Highway, that links Kathmandu Valley with the Eastern Terai region, and Tribhuvan Highway that links Kathmandu with the Indian border, have many hairpin bends.
- In West Sumatra, Indonesia, there are two sections of road particularly famous for its hairpins: Kelok Ampek-Puluh-Ampek near Lake Maninjau, and Kelok Sembilan near Payakumbuh.
- In Sri Lanka, on the 41 km long Kandy-Padiyathalawa road via Mahiyangana there are 18 hairpin bends, popularly known as Daha ata wanguwa. 
- The Mount Hotham Pass on the Great Alpine Road in Victoria has numerous hairpin bends, as do the other roads in the region.
- Galston Gorge in New South Wales. Vehicles like towed caravans are forbidden on this road, lest the caravan gets jammed and delays other traffic. Special penalties apply if overlength vehicles attempted to take this route.
- Macquarie Pass in New South Wales, which winds through Macquarie Pass National Park has numerous hairpin bends which used to be so tight that semi-trailers had to stop and reverse to get around.
- Kangaroo Valley Road in New South Wales, located near Berry.
- Ben Lomond Road in Tasmania has 6 hairpin bends known as "Jacobs Ladder", which is a popular descent for cyclists 
- Corkscrew Road in Montacute, South Australia starts at Gorge Road and winds, as its name suggests, up to Montacute Road. This 2.4-kilometre (1.5 mi) road has become famous through the Tour Down Under King of the Mountain climb for the difficulty of riding up the steep and sharp bends. 
- Western end of Cahill Expressway in Sydney.
- Fairmont Hotel Hairpin is the slowest turn in Formula One
- 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, to increase overtaking opportunities or simply increase the lap length without increasing the area occupied by the track.
- Martinsville Speedway is a paper clip shaped short track on the NASCAR Sprint Cup Series circuit, measuring around 0.5 miles (0.80 km) in length.
- The eleventh turn at Sonoma Raceway is a hairpin turn used in NASCAR.
If a railway curves back on itself like a hairpin turn, it is called a horseshoe curve. However, the radius of curvature is much larger than that of a typical road hairpin. See this example at Zlatoust  or Hillclimbing for other railway ascent methods.
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.)
HAIRPIN TURN INFORMATION
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