Hairpin turn

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D2204 road ascends to the Col de Brauss using hairpin bends in the French Alps.

Some of the 48 hairpin turns near the top of the northern ramp of the Stilfserjoch (Passo dello Stelvio)

Hairpin turn on the Mont Ventoux in France

A nearly 180-degree turn in a road, trail, or ramp is called a hairpin turn (also hairpin bend or, if in a trail, a switchback). It is named for its geometric resemblance to a hairpin. These 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. An alternative in trail-building is the stairway.

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.

Some highways with switchback (hairpin) turns include:

Europe:

• Stelvio Pass with its 48 Spitzkehren on the northern ramp alone is one of the most famous
• in rallying, the cars slide sideways around hairpins bends 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 featire 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

• Lombard Street (San Francisco)
• California State Highway 92 east of Half Moon Bay, California
• U.S. Highway 93 on the Arizona side of Hoover Dam
• Arizona State Highway 89A as it enters Oak Creek Canyon
• California State Highway 1 south of Bodega Bay; it is shown in Alfred Hitchcock's film The Birds, is still in use, and looks much as it did during the filming
• 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

• 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

Disadvantages

A disadvantage of a hairpin bend is that it is awkward for large vehicles to traverse. There is a risk that a large vehicle may get stuck, which blocks the road and delays other traffic. Sometimes the road authorities prohibits large vehicles or vehicles towing trailers from using a section or road containing hairpin bends.

Railways

• If the railway curves back on itself, it might be called
• * a Horseshoe curve as at
• ** Kittanning Gap
• ** Arnold
• ** Picton, Australia

• If the railway has to reverse direction it called
• * a switchback
• * or Zig Zag

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