This article needs additional citations for verification . (July 2014) (Learn how and when to remove this template message)
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. 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.
In trail building, an alternative to switchbacks is the stairway.
This section possibly contains original research . (April 2018) (Learn how and when to remove this template message)
Some roads with switchbacks (hairpin turns) include:
The eastern ramp of the Liniebrug, a bike and footbridge built over the Amsterdam-Rhine Canal near Nigtevecht in the Netherlands in 2018, consists of a pair of hairpin bends.
If a railway curves back on itself like a hairpin turn, it is called a horseshoe curve. The Pennsylvania Railroad built a famous one in Blair County, Pennsylvania ascending 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 Zlatoustor 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.
A horseshoe curve is a class of climbing curve in a roadbed which reverses turn direction (inflection) twice on either side of a single tight curve that varies through an angle of about 180 degrees or more.
The Raurimu Spiral is a single-track railway spiral, starting with a horseshoe curve, overcoming a 139-metre (456 ft) height difference, in the central North Island of New Zealand, on the North Island Main Trunk railway (NIMT) between Wellington and Auckland. It is a notable feat of civil engineering, having been called an "engineering masterpiece." The Institute of Professional Engineers of New Zealand has designated the spiral as a significant engineering heritage site.
Skyline Drive is a 105-mile (169 km) road that runs the entire length of the National Park Service's Shenandoah National Park in the Blue Ridge Mountains of Virginia, generally along the ridge of the mountains. The drive's northern terminus is at an intersection with U.S. Route 340 (US 340) near Front Royal, and the southern terminus is at an interchange with US 250 near Interstate 64 (I-64) in Rockfish Gap, where the road continues south as the Blue Ridge Parkway. The road has intermediate interchanges with US 211 in Thornton Gap and US 33 in Swift Run Gap. Skyline Drive is part of Virginia State Route 48, which also includes the Virginia portion of the Blue Ridge Parkway, but this designation is not signed.
Pennsylvania Route 61 is an 81.8-mile-long (131.6 km) state highway in the U.S. state of Pennsylvania. The route is signed on a north–south direction, running from U.S. Route 222 Business in Reading northwest to US 11/US 15 in Shamokin Dam. PA 61 heads north from Reading through Berks County to Hamburg, where it meets Interstate 78 (I-78)/US 22. The route continues into the Coal Region in Schuylkill County and heads through Schuylkill Haven, Pottsville, Frackville, and Ashland. PA 61 passes through the southern part of Columbia County, where it turns west in Centralia, before it heads into Northumberland County and runs west through Mount Carmel, Kulpmont, Shamokin, and Sunbury. The route crosses the Susquehanna River into Snyder County and soon reaches its northern terminus.
Pennsylvania Route 309 is a state highway which runs for 134 miles (216 km) through Pennsylvania in the United States. The route runs from the interchange between PA 611 and Cheltenham Avenue on the border of Philadelphia and Cheltenham Township north to an intersection with PA 29 in Bowman Creek, a village in Monroe Township in Wyoming County. It connects Philadelphia and its northern suburbs to Allentown, Hazleton, and Wilkes-Barre. PA 309 heads north from Philadelphia and becomes a freeway called the Fort Washington Expressway through suburban areas in Montgomery County, passing through Fort Washington, before becoming a surface road called Bethlehem Pike and running through Montgomeryville. In Bucks County, the route has a freeway section bypassing Sellersville before passing through Quakertown as a surface road. PA 309 heads into the Lehigh Valley and joins Interstate 78 (I-78) on a freeway bypassing Allentown before splitting to the north and running through rural areas as a surface road. The route continues north into the Coal Region and passes through Tamaqua before it reaches Hazleton. PA 309 heads into the Wyoming Valley and passes through the Wilkes-Barre area on a freeway alignment along I-81 and the North Cross Valley Expressway before turning into a surface road again and running through Dallas before reaching its northern terminus.
Pennsylvania Route 26 is a 125.5-mile (202.0 km) highway in the south-central area of Pennsylvania. Its northern terminus is at PA 150 northwest of Howard; its southern terminus is at the Maryland state line near Barnes Gap in Union Township. Two major destinations along this route are Raystown Lake near Huntingdon and the Pennsylvania State University at State College.
Pennsylvania Route 29 is a 118-mile-long (190 km) north–south state highway that runs through most of eastern Pennsylvania. The route currently exists in two segments, a southern segment and a northern segment. The southern segment runs from U.S. Route 30 near Malvern north to Interstate 78 (I-78)/PA 309 near Allentown. The northern segment runs from I-81 in Ashley north to the New York-Pennsylvania border near Brookdale, where the road becomes New York State Route 7.
In the U.S. state of Pennsylvania, U.S. Route 30 runs east–west across the southern part of the state, passing through Pittsburgh and Philadelphia on its way from the West Virginia state line east to the Benjamin Franklin Bridge over the Delaware River into New Jersey. In Pennsylvania, US 30 runs along or near the transcontinental Lincoln Highway, an auto trail which ran from San Francisco, California to New York City before the U.S. Routes were designated.
U.S. Route 6 (US 6) travels east–west near the north edge of the U.S. state of Pennsylvania from the Ohio state line near Pymatuning Reservoir east to the Mid-Delaware Bridge over the Delaware River into Port Jervis, New York. It is the longest highway segment in the Commonwealth. Most of it is a two-lane rural highway, with some freeway bypasses around larger towns. Except east of Dunmore, where it is paralleled by Interstate 84 (I-84), it is the main route in its corridor. What is now I-80—the Keystone Shortway—was once planned along the US 6 corridor as a western extension of I-84. The corridor was originally the Roosevelt Highway from Erie, Pennsylvania to Port Jervis, New York, designated Pennsylvania Route 7 (PA 7) in 1924. The PA 7 designation soon disappeared, but as US 6 was extended and relocated, the Roosevelt Highway followed it. The Pennsylvania section of US 6 was renamed the Grand Army of the Republic Highway in 1946; this name was applied to its full transcontinental length by 1953.
Pennsylvania Route 44 is a 149.24 mi (240.18 km)-long state highway in the U.S. state of Pennsylvania. The route is designated from Interstate 80 (I-80) and PA 42 in Buckhorn to the New York state line near New York State Route 417 in Ceres Township.
Pennsylvania Route 16 is a 43-mile-long (69 km) east–west state route located in southern Pennsylvania, United States. The western terminus of the route is at U.S. Route 522 in McConnellsburg. The eastern terminus is at the Mason–Dixon line in Liberty Township, where the road continues into Maryland as Maryland Route 140. PA 16 is a two-lane road that runs through rural areas in Fulton, Franklin, and Adams counties. The route heads east from McConnellsburg and crosses Tuscarora Mountain into Franklin County, where it continues east into the agricultural Cumberland Valley. Here, the passes through Mercersburg, Greencastle, and Waynesboro. PA 16 heads east through the South Mountain range, where it heads into Adams County and passes through Carroll Valley before coming to the Maryland border. PA 16 intersects several roads including PA 456 in Cove Gap, PA 75 and PA 416 in Mercersburg, PA 995 in Upton, US 11 and Interstate 81 (I-81) in Greencastle, PA 316 and PA 997 in Waynesboro, and PA 116 in Carroll Valley. The road's main name is Buchanan Trail in honor of 15th President James Buchanan, who was born near the road in Cove Gap.
Pennsylvania Route 74 is a 96.4-mile-long (155.1 km) north–south state highway located in central Pennsylvania. The southern terminus of the route is at the Mason–Dixon line southwest of Delta, where PA 74 continues into Maryland as Maryland Route 165. The northern terminus is at PA 75 south of Port Royal.
Pennsylvania Route 93 is a 41-mile-long (66 km) state route located in Carbon, Luzerne, and Columbia counties in northern Pennsylvania. The southern terminus is at U.S. Route 209 in Nesquehoning, about half-way from PA just north of the 1800s community of Lausanne Landing, the southern toll station of the Lausanne & Nescopeck Turnpike (1804)—along whose path the highway was built. The northern terminus of the route is at PA 487 in Orangeville, the part of the road west of the Susquehanna and Berwick once being part of the Susquehanna & Tioga Turnpike (1806).
Pennsylvania Route 147 is a north–south route that runs for 58.3 miles (93.8 km) along the east shore of the Susquehanna River in central Pennsylvania, United States. The southern terminus is at an interchange with U.S. Route 22 and US 322 in Reed Township. The northern terminus is at an interchange with Interstate 80 (I-80) and I-180 in Turbot Township.
Pennsylvania Route 641 is a state route located in Central Pennsylvania in the United States. The route is 57.9 miles (93.2 km) long and runs from U.S. Route 522 near Shade Gap east to US 11/US 15 in Camp Hill. PA 641 heads east from Shade Gap in Huntingdon County and immediately crosses PA 35 before it heads across Tuscarora Mountain into Franklin County. The route intersects PA 75 in Spring Run before it crosses Kittatinny and Blue mountains and reaches a junction with PA 997 in Roxbury. PA 641 heads into the agricultural Cumberland Valley and enters Cumberland County, where it intersects PA 696 in Newburg and PA 233 in Newville before reaching Carlisle. In Carlisle, the route runs concurrent with US 11 and PA 74 on High Street and crosses PA 34 in the center of town. East of here, PA 641 has an interchange with Interstate 81 (I-81) and heads to Mechanicsburg, where it intersects PA 114. The route continues through the western suburbs of Harrisburg and has an interchange with US 11/PA 581 before ending in Camp Hill. PA 641 has a truck route, PA 641 Truck, that bypasses the winding stretch across Kittatinny Mountain.
Pennsylvania Route 144 is a state highway located in the U.S. state of Pennsylvania, covering a distance of about 109 miles (175 km). The southern terminus is located at U.S. Route 322 (US 322) in Potter Township while the northern terminus is located at U.S. Route 6 in Galeton. Between Snow Shoe and Renovo, PA 144 is known as the High Plateau Scenic Byway, a Pennsylvania Scenic Byway.
Pennsylvania Route 225 is a 48.5-mile-long (78.1 km) state highway located in Dauphin and Northumberland Counties in Pennsylvania. The southern terminus is at an interchange with U.S. Route 22 /US 322 in Dauphin. The northern terminus is at PA 61 in Shamokin. PA 225 is mostly a two-lane undivided road running through mountain and valley areas in the central part of the state. The route serves the communities of Halifax, Elizabethville, Berrysburg, Pillow, and Trevorton. PA 225 intersects PA 325 north of Dauphin, PA 147 in Halifax, US 209 in Elizabethville, PA 25 in Berrysburg, and PA 890 in Trevorton.
Pennsylvania Route 274 is a 44-mile-long (71 km) state highway located in Franklin and Perry Counties in Pennsylvania. The western terminus is at PA 75 in the Fannett Township community of Doylesburg. The eastern terminus is at an interchange with U.S. Route 11 /US 15 in Duncannon. PA 274 is a two-lane undivided road that runs through rural areas in the Ridge-and-Valley Appalachians. The route heads northeast and crosses Conococheague Mountain, at which point it leaves Franklin County for Perry County. PA 274 continues through agricultural valleys and intersects PA 17 in Blain, PA 850 in Loysville and PA 233 and PA 74 in Green Park. In New Bloomfield, PA 274 intersects PA 34 and turns southeast for a concurrency with that route to Mecks Corner. From here, the route continues east to Duncannon.
Norwegian County Road 63 is a Norwegian county road in Møre og Romsdal county and a very small part in Innlandet county, Norway. It begins at Norwegian National Road 15 along the lake Langvatnet in Skjåk Municipality in Innlandet county and it heads north where it ends at the junction with the European route E136 highway near the town of Åndalsnes in Rauma Municipality, Møre og Romsdal county. The route runs for 103.6 kilometres (64.4 mi) including a single ferry crossing over the Norddalsfjorden. The vast majority of the road is in Møre og Romsdal county, only the southernmost 2.5 kilometres (1.6 mi) lie in the extreme western part of Innlandet county. Both the Langvatnet–Geiranger and Trollstigen sections of the road are closed during winter and spring due to the weather conditions. The road passes by a number of notable landmarks, which has led to the earmarking of the route as national tourist route.
State Route 91 is a state highway in the northeastern portion of the U.S. state of Tennessee, in the area known as the Tri-Cities region. The route connects Johnson City with Damascus, Virginia via Elizabethton, Hunter, and Mountain City.
Media related to Hairpin turns at Wikimedia Commons