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. Such turns in ramps and trails may be called switchbacks in American English, by analogy with switchback railways.
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.
The road from Frangokastello to Kallikratis in Crete has 27 tight bends. Due to the mountainous profile of the country, many public streets in Greece have tight bends. The asphalt is also slippery in these areas, making it easy to lose traction (and thus control). The situation worsens with the first rains after the long dry summer, making the asphalt more slippery than usual.
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"
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 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 Chūzenji, 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 kana syllabary; 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). In Aomori Prefecture, the Tsugaru Iwaki Skyline is a toll road that allows drivers to ascend 2,644 feet (806 m) with an average gradient of 8.66% and sections up to 10%; to 8th station on the stratovolcano, Mount Iwaki. The road is considered to be one of the most dangerous mountain roads in the world due to the gradient and the constant 69 hairpin turns.
In Myanmar, 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.
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.
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.
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.
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.