Railway layout for steep climbs
Spiral viaduct of theBernina Express near Brusio, Switzerland. Aspiral (sometimes called aspiral loop or justloop ) is a technique employed byrailways to ascend steep hills.
A railway spiral rises on a steady curve until it has completed a loop, passing over itself as it gains height, allowing the railway to gain vertical elevation in a relatively short horizontal distance. It is an alternative to azig-zag , and avoids the need for the trains to stop and reverse direction while ascending. If the train is longer than the length of each loop it may be possible to view it looping above itself.[ 1] [ 2]
The term "loop" is also often used for a railway that curves sharply and goes back on itself: if the railway crosses itself, then it forms a spiral orhelix ; otherwise, it forms the much more commonhorseshoe curve or bend .[ 3] [ 4]
Guanjiao Spiral onQinghai–Tibet Railway at night. The route containing the spiral was replaced bya 32-km long tunnel (at the time of completion thelongest in China) in 2014. Replica of the Brusio Spiral Viaduct at10°28′44″N 84°49′25″W / 10.47900°N 84.82374°W /10.47900; -84.82374 Tren Turistico Arenal , 10 km east of Nuevo Arenal, Guanacaste.[ 38] [ 39]
Loop (Agony Point) on the DHR, India TheDarjeeling Himalayan Railway originally had five or six spirals but only five in operation at any one time. The line also has six reverses orzig-zags .[ 56] [ 57]
Okoba spiral andzig zag inHisatsu Line , Japan Spiral loop, west ofRainbow Bridge in Tokyo, Japan. There are three spirals on the1,000 mm (3 ft 3+ 3 ⁄8 in )gauge railway line fromKenya to Uganda . This railway has been superseded by theMombasa–Nairobi Standard Gauge Railway , which has removed the need for spirals by constructing tunnels and bridges.[ 73] [ 74] [ 75] [ 76]
Spiral inThazi –Taunggyi line,Myanmar Geumdae 2nd Tunnel inJungang Line ,South Korea Toua spiral tunnel on theRhB Albulabahn Triple spiral loop on theAlishan Forest Railway The bridge on the spiral loop atDduallt on theFfestiniog Railway , Wales. Tehachapi Loop , on theUnion Pacific Railroad , California, United States, viewed from the air.1903 view of Riflesight Notch loop, nearRollins Pass in Colorado Tehachapi Loop , atTehachapi, California at35°12′03″N 118°32′13″W / 35.200833°N 118.536944°W /35.200833; -118.536944 Southern Pacific Railroad, now part ofUnion Pacific Railroad .[ 117] [ 118] Williams Loop , east ofEast Quincy, California at39°54′36″N 120°48′29″W / 39.910131°N 120.807949°W /39.910131; -120.807949 Western Pacific Railroad now part ofUnion Pacific Railroad .[ 119] Hiwassee Loop, also known as the Hook and Eye; 2 miles NNE ofFarner, Tennessee at35°10′53″N 84°17′59″W / 35.181257°N 84.299707°W /35.181257; -84.299707 Atlanta, Knoxville and Northern Railway now operated as aheritage railroad by theTennessee Valley Railroad Museum , which operates excursion trains fromEtowah, Tennessee toCopperhill, Tennessee via the loop, as well as trains just to the loop and back from Etowah.[ 120] Georgetown Loop , atGeorgetown, Colorado at39°42′02″N 105°42′32″W / 39.7005794°N 105.7087871°W /39.7005794; -105.7087871 Colorado Central Railroad . The spiral was completed in 1884, abandoned and dismantled in 1939, rebuilt between 1972 and 1984 and is now owned byHistory Colorado and operated as theGeorgetown Loop Railroad .[ 121] TheMAX Red Line , alight rail line inPortland, Oregon , loops over itself at45°31′51″N 122°33′49″W / 45.5307°N 122.5636°W /45.5307; -122.5636 Gateway Transit Center .[ 122] In the Loop District of theAlaska Railroad at60°39′36″N 149°02′29″W / 60.660062°N 149.041251°W /60.660062; -149.041251 mileposts 48 and 51 northeast ofSeward, Alaska , there was a spiral and ahorseshoe curve both on an extensive range of timbertrestles up to 106 feet high. Track relocation in 1951 removed all of this but added a new horseshoe at milepost 48.[ 123] Abandoned spiral at Riflesight Notch Loop atRollinsville, Colorado at39°54′00″N 105°42′47″W / 39.9001°N 105.7130°W /39.9001; -105.7130 Denver and Salt Lake Railway route overRollins Pass . The spiral was bypassed by theMoffat Tunnel built in 1928, and was dismantled in 1935.[ 124] Abandoned spiral called Double Circle, or Double Loop, or The Golden Circle, at39°59′07″N 112°02′39″W / 39.985246°N 112.044138°W /39.985246; -112.044138 Eureka, Utah on the former Tintic branch of theDenver and Rio Grande Western Railroad . It was bypassed in 1940 and the branch removed in 1943.[ 125] [ 126] [ 127] Abandoned spiral on theRoaring Camp and Big Trees Railroad at37°02′33″N 122°03′54″W / 37.0426°N 122.0649°W /37.0426; -122.0649 switchbacks after a trestle fire in 1976.[ 128] ^ Christian Wolmar (1 May 2014).The Iron Road: The Illustrated History of Railways ISBN 978-0-241-18186-7 ^ S. M. Yameen Nachsch (1972).Railway Engineering ^ William W. 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