Spiral (railway)

For the engineering term applying to railway track geometry, see Track transition curve.
Spiral viaduct near Brusio, Switzerland.

A spiral (sometimes called a spiral loop or just loop) is a technique employed by railways 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 a zig-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; otherwise, it forms the much more common horseshoe curve or bend.[3][4]

A spiral loop is not the same as the transition spiral or spiral easement used to provide a transition from a tangent into a horizontal circular curve. Spiral easement is used to avoid abrupt changes in the sideward acceleration experienced by a railway vehicle and the passengers in the vehicle approaching the horizontal circular curve and to prevent abrupt forces and discomfort.[5][6][7]

List of spirals

This list is incomplete; you can help by expanding it.





People's Republic of China





Loop (Agony Point) on the DHR, India

The Darjeeling Himalayan Railway originally had five or six spirals but only five in operation at any one time. The line also has six reverses or zig-zags.[30]





Okoba spiral and zig zag in Hisatsu Line, Japan


South Korea

Geumdae 2nd Tunnel in Jungang Line, South Korea



Spiral in Thazi Taunggyi line, Myanmar

New Zealand




South Africa


Sri Lanka


Toua spiral tunnel on the RhB Albulabahn


Triple spiral loop on the Alishan Forest Railway


United Kingdom

The bridge on the spiral loop at Dduallt on the Ffestiniog Railway, Wales.

United States

Tehachapi Loop, on the Union Pacific Railroad, California, United States, viewed from the air.
1903 view of Riflesight Notch loop, near Rollins Pass in Colorado

See also


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  2. S. M. Yameen Nachsch (1972). Railway Engineering. Caravan Book House.
  3. William W. Hay (16 June 1982). Railroad Engineering. John Wiley & Sons. pp. 231–. ISBN 978-0-471-36400-9.
  4. Jim Harter (2005). World Railways of the Nineteenth Century: A Pictorial History in Victorian Engravings. JHU Press. ISBN 978-0-8018-8089-6.
  5. Rankine, William (1883). A Manual of Civil Engineering (17th ed.). Charles Griffin. pp. 651–653.
  6. International Correspondence Schools (1908). The Transition Spiral, Earthwork, Railroad Location, Trestles, Trackwork, Railroad Buildings and Miscellaneous Structures, Highways, Pavements, City Surveying, City Streets, Construction Drawing. International Textbook Company.
  7. Coleman O'Flaherty (1997). Transport Planning and Traffic Engineering. Elsevier. pp. 331–. ISBN 978-0-340-66279-3.
  8. Axel Borsdorf; Christoph Stadel (12 March 2015). The Andes: A Geographical Portrait. Springer. pp. 273–. ISBN 978-3-319-03530-7.
  9. The Australian encyclopaedia. Michigan State University Press. 1958.
  10. William Alan Bayley (1973). Standard Gauge Railway Across Australia. Austrail Publications. ISBN 978-0-909597-09-2.
  11. 1 2 John Brian Hollingsworth (1982). Atlas of the world's railways. Bison.
  12. 1 2 3 4 Brendan Fox; et al. (2011). The Thomas Cook Rail Map of Europe (Map) (18th ed.). 1:4000000. Cartography by Mary Spence. Thomas Cook Publishing. ISBN 978-1-84848-356-9.
  13. 1 2 3 4 5 6 7 Ball, Mike (1 May 2016). European Railway Atlas.
  14. Jane's World Railways. Sampson Low, Marston ; New York: Rand McNally. 1960.
  15. Graeme Pole (1 January 1995). The Spiral Tunnels and the Big Hill: A Canadian Railway Adventure. Altitude Publishing Canada Limited. ISBN 978-1-55153-907-2.
  16. Barry D. Stewart (2004). Across the Land --a Canadian Journey of Discovery. Trafford Publishing. pp. 224–. ISBN 978-1-4120-2276-7.
  17. L.D. Cross (21 July 2014). High Peaks Engineering: Rocky Mountain Marvels. Heritage House Publishing Co. pp. 93–. ISBN 978-1-927527-80-1.
  18. Les Harding (5 February 2008). The Newfoundland Railway, 1898-1969: A History. McFarland. pp. 86–. ISBN 978-1-4766-0839-6.
  19. Trinity Loop
  20. Art Downs (1 May 1985). Incredible Rogers Pass. Heritage House Publishing Co. pp. 27–. ISBN 978-0-919214-08-8.
  21. 1 2 Quail Map Company (1 January 1993). China Railway Atlas (first ed.). Quail Map Company. ISBN 978-0-900609-94-7.
  22. Yuan Lei (2014-12-29). "袁蕾, 吐库二线正式开通运营 南疆铁路进入电气化时代 新疆日报" [Yuan Lei, spit library second-tier official opening and operation of the Southern Xinjiang Railway electrification into the Xinjiang Daily Times (Machine generated)] (in Chinese). Retrieved 2016-07-04.
  23. 1 2 Benjaminse Uitgeverij BV (2013). A Travellers' Railway map of Europe (Map) (3rd ed.). 1:3800000. Cartography by Carto Studio BV. Benjaminse Uitgeverij BV. ISBN 978-90-77899-09-0.
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  26. fr:Ligne transcévenole
  27. C. Harald Harlinghausen; Hartmuth Merleker (1986). Germany Federal Republic. Nagel. ISBN 978-2-8263-0761-7.
  28. Great Britain. Naval Intelligence Division (1945). Germany: Ports and communications. Naval Intelligence Division.
  29. 1 2 3 Terry Martin (2006). The Iron Sherpa: The Story of the Darjeeling Himalayan Railway, 1879-2006. The Iron Sherpa by T. Martin. ISBN 978-1-900622-10-3.
  30. Going Loopy. Darjeeling Himalayan Railway Society. 2005. ISBN 0-9541602-2-3.
  31. The Great Indian Railway Atlas. Samit Roychoudhury. 2005. ISBN 81-901457-0-3.
  32. irfca.org
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  39. 1 2 National Defense Transportation Journal. National Defense Transportation Association. 1953.
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  44. 1 2 Collins Road Atlas: Spain and Portugal (Road Atlas). Collins. 2002. ISBN 0007140738.
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