Spiral (railway)

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]

^ Christian Wolmar (1 May 2014). The Iron Road: The Illustrated History of Railways. Dorling Kindersley Limited. pp. 170–. ISBN 978-0-241-18186-7.
^ S. M. Yameen Nachsch (1972). Railway Engineering. Caravan Book House.
^ William W. Hay (16 June 1982). Railroad Engineering. John Wiley & Sons. pp. 231–. ISBN 978-0-471-36400-9.
^ Jim Harter (2005). World Railways of the Nineteenth Century: A Pictorial History in Victorian Engravings. JHU Press. ISBN 978-0-8018-8089-6.

[Wolmar2014-1] Christian Wolmar (1 May 2014). The Iron Road: The Illustrated History of Railways. Dorling Kindersley Limited. pp. 170–. ISBN 978-0-241-18186-7.

[Nachsch1972-2] S. M. Yameen Nachsch (1972). Railway Engineering. Caravan Book House.

[Hay1982-3] William W. Hay (16 June 1982). Railroad Engineering. John Wiley & Sons. pp. 231–. ISBN 978-0-471-36400-9.

[Harter2005-4] Jim Harter (2005). World Railways of the Nineteenth Century: A Pictorial History in Victorian Engravings. JHU Press. ISBN 978-0-8018-8089-6.

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