 |
This article needs additional citations for verification. Please help improve this articlebyadding citations to reliable sources. Unsourced material may be challenged and removed.
Find sources: "Hairpin turn" – news · newspapers · books · scholar · JSTOR (July 2014) (Learn how and when to remove this message) |
Ahairpin turn (also hairpin bendorhairpin 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 switchbacksinAmerican 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.
On occasion, the road may loop completely, using a tunnel or bridge to cross itself at a different elevation (example on Reunion Island: 21°10′52″S 55°27′17″E / 21.18111°S 55.45472°E / -21.18111; 55.45472; example near Ashland, Oregon 42°05′31″N 122°35′21″W / 42.09194°N 122.58917°W / 42.09194; -122.58917). When this routing geometry is used for a rail line, it is called a spiral, or spiral loop.
Intrail building, an alternative to switchbacks is the stairway.
If a railway curves back on itself like a hairpin turn, it is called a horseshoe curve. The Pennsylvania Railroad built oneinBlair County, Pennsylvania, which ascends the Eastern Continental Divide from the east. However, the radius of curvature is much larger than that of a typical road hairpin. See this example at Zlatoust[1]orHillclimbing 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.[2]
Media related to Hairpin turns at Wikimedia Commons
