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






Guanjiao Spiral on Qinghai–Tibet Railway at night, it was replaced by a 32-km long tunnel in 2014





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.[40][41]





Okoba spiral and zig zag in Hisatsu Line, Japan


Three spirals on the Kenya to Uganda 1,000 mm (3 ft 3 38 in) gauge Railway Line, originally known as the Uganda Railway despite being wholly in Kenya, then as the Kenya and Uganda Railways and Harbours followed by a time as the East African Railways and Harbours Corporation before being split into the Kenya Railways Corporation and Uganda Railways Corporation.[57][58] The spirals are at:

This railway has ceased operations and has been superseded by the Mombasa–Nairobi Standard Gauge Railway which has removed the need for spirals by constructing tunnels and bridges.[59][60][61][62]

South Korea

Geumdae 2nd Tunnel in Jungang Line, South Korea




Spiral in Thazi – Taunggyi line, Myanmar

New Zealand



(Tуапсе) through Gornyy to Belorechensk (Белореченск).[citation needed]



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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External links