Spiral viaduct of the Bernina Express 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 or helix; otherwise, it forms the much more common horseshoe curve or bend.[3][4]
^ abcdBrendan Fox; et al. (2011). The Thomas Cook Rail Map of Europe (Map) (18th ed.). 1:4000000. Cartography by Mary Spence. Thomas Cook Publishing. ISBN978-1-84848-356-9.
^ abcdBall, Mike (20 March 2017). European Railway Atlas Regional Series, Romania, Bulgaria and Moldova.
^ abcdefgBall, Mike (1 May 2016). European Railway Atlas.
^ abcПодробна карта на България (A detailed Map of Bulgaria) (Map). 1:380000. ДатаМап-Европа ООД (DataMap Europe). 2014. ISBN978-954-519-036-0.
^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). Archived from the original on August 22, 2016. Retrieved 2016-07-04.
^"Long Tunnels". European Tribune. 12 June 2016. Retrieved 18 November 2020.
^Devereux, Nigel (September 2017). "Costa Rican rail variety". The Railway Magazine. Mortons Media Group Ltd.: 104.
^ abBall, Mike (3 September 2017). European Railway Atlas Regional Series, The Balkans.
^ abBenjaminse Uitgeverij BV (2013). A Travellers' Railway map of Europe (Map) (3rd ed.). 1:3800000. Cartography by Carto Studio BV. Benjaminse Uitgeverij BV. ISBN978-90-77899-09-0.
^ abcdeBall, Mike (15 July 2016). European Railway Atlas Regional Series, Italy.
^ abBraun, Michel (April 2017). "The Col de Tende Line: A tortuous route and history". Today's Railways Europe. Sheffield, England: Platform 5 Publishing.
^Ellison, Paul (December 1968). "Guinness Brewery Tramways". The Industrial Railway Record. The Industrial Railway Society. pp. 337–347. Retrieved 8 December 2017.
^Peaty, Ian P. (1985). Brewery Railways. Newton Abbot: David and Charles. pp. 42–43. ISBN0-7153-8605-0.
^ abcdefAtlante Stradale Italia (Road Atlas). Instituto Geografico DeAgostini. 2009. ISBN9788851114398.
^"On Burma Corporation Ltd". Australasian Institute of Mining and Metallurgy. Australasian Institute of Mining Engineers: 91. 1922. Retrieved 23 December 2017.
^Owen, Roy (1996). Norwegian railways : from Stephenson to high speed. Hitchin: Balholm Press. p. 159. ISBN0-9528069-0-8. OCLC43127416.
^Sigurd H. Unneberg, Sem og Slagen, en bygdebok Bind 2, Kulturhistorie, del 2 . Tønsberg: Høgskolen i Vestfold, 2001. Relevant chapter is online hereArchived 2016-03-03 at the Wayback Machine(in Norwegian)