Spiral (railway)

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 360-degree 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 of sufficient length, it is possible to view the train looping onto itself.

A spiral loop should not be confused with the civil engineering spiral curve used to provide a transition from a tangent into a horizontal circular curve. The civil engineering spiral curve is a curve of uniformly decreasing radius (beginning at infinite and ending at the radius of the circular curve) used to minimize rolling stock sway, and also in highway curves for aesthetic reasons.


On a railway climbing at a gradient of 1 in 40 (2.5%, or 25 m per km) a 360-degree spiral at 350 m radius will add 1100 m to the forward journey and 27 m to the vertical climb. Unless the topography has a suitably shaped hill, the spiral is likely to be in tunnel, increasing construction costs and creating problems if steam locomotives are employed. If a convenient side valley is available, then a horseshoe curve may be possible.

The spiral needs to climb about 6 m in order to bridge itself. With steam locomotives and to a lesser extent with diesel locomotives, the gradient in the tunnel should be less than the ruling grade to avoid problems with fumes and dampness causing the driving wheels to slip.

List of spirals


* Kenya-Uganda four spirals on the Kenya to Uganda line.


* Bethungra Spiral two very short tunnels, uphill track in spiral at 1 in 66 gradient, downhill track plain at 1 in 40 gradient
* Cougal Spiral one short and one long tunnel, single track


* Avramovo gauge

* between Khandwa and Hingoli, metre gauge,


* Numerous spirals through very mountainous regions, mostly entirely in tunnel and single track


* The St. James's Gate Brewery, Dublin, Ireland had an internal 1 ft 10 in gauge railway with a loop in a tunnel to gain height between buildings [http://www.talyllyn.co.uk/ngrm/guinness.html?printable=true]


* At Iselle di Trasquera on the SBB.


* Jetsu Line has two spirals, track towards Tokyo only
* Hokuriku Main Line from Tsuruga Station to Shin-Hikita Station, track for Maibara Station only
* Hisatsu line between Yatake Station and Okoba Station, with a zig zag in the loop
* Tosa Kuroshio Railway Nakamura Line between Kawaoku S.B. and Kaina Station
* Yurikamome, western approach to the Rainbow Bridge


* One loop at Anjiro on the main line from Antananarivo to Toamasina.


* Two spirals on the Burmah Mines Railway [http://www.internationalsteam.co.uk/trains/bmines.htm]

New Zealand

* Raurimu Spiral on the North Island Main Trunk, single track, suitable hill, two short tunnels. See [http://www.nzetc.org/tm/scholarly/Gov10_01Rail-fig-Gov10_01Rail035a.html Map] and [http://www.nzetc.org/tm/scholarly/Gov11_06Rail-fig-Gov11_06Rail035a.html Photo] .
* Driving Creek Railway


* Flåmsbana: between Myrdal and Flåm - tunnels that spiral in and out of the mountainside.


*Telgart Loop ( [http://rail.sk/skhist/tunely/173/01.htm Telgártska sľučka ] - Slovak language)

outh Korea

* between Bangok station and Chiak station on Jungang Line - one loop, single track. New double track tunnel is under construction to replace loop tunnel.
* between Jungnyeong station (죽령역) and Huibangsa station (희방사역) on the Jungang Line - one loop, single track.


* Cargol Tunnel on the Ripoll - La Tour de Carol (France) line

Sri Lanka

* Demodera


* Gotthardbahn has five spirals and two turns, entirely in tunnel, double track, standard gauge
* Bern-Lötschberg-Simplon railway, standard gauge
* RhB Albulabahn has several spiral tunnels, single track, metre gauge
* RhB has an open spiral mainly on a bridge (Berninabahn, near Brusio), single track, metre gauge
* Former Furka-Oberalp-Bahn, now Dampfbahn Furka-Bergstrecke heritage railway, has one spiral tunnel, single track, cog rail, metre gauge, catenary removed
* Former Furka-Oberalp-Bahn, now Matterhorn-Gotthard-Bahn, between Grengiols and Laax, single track, metre gauge, cog rail, entirely in tunnel


* Dulishan loop is a triple spiral (two clockwise and one counter-clockwise), Alishan (阿里山) Forest Railway, narrow gauge, single track

United Kingdom

* Dduallt Loop, Ffestiniog Railway in Wales, RailGauge|23.5 gauge
* The line from Moorswater cement terminal, through Coombe Junction and Liskeard on the Looe Valley Line and on over Moorswater Viaduct forms a complete spiral, climbing up to join the main line at Liskeard. Not all parts are used by passenger trains.

United States

* California, Williams Loop
* California, Tehachapi Loop
* California, Roaring Camp Loop - RailGauge|3ft gauge (abandoned after fire, trestles still partly standing)
* Colorado, Georgetown Loop
* Ophir Loop - Rio Grande Southern Railroad - RailGauge|3ft gauge (abandoned)

Spirals are not generally used on tramways (street running or reserved track) or light rail lines because trams traditionally have all wheels powered, so can climb much steeper direct gradients than railways.


Roads sometimes use a spiral to gain height in a confined space:
* Cahill Expressway, Sydney, New South Wales, Australia.
* Lincoln Tunnel, approach road to west portal, Weehawken, New Jersey, USA.
* Iron Mountain Road, Custer State Park, South Dakota, USA.
* Sa Calobra, Majorca, Spain({ [coord|39.831968|2.81574|type:landmark_region:ES_scale:5000
* New Clear Water Bay Road, New Kowloon, Hong Kong (coord|22.331717|114.224617|region:HK_type:landmark_scale:1000
* N8 Bypass Brienzwiler, Switzerland (coord|46.750521|8.108833|type:landmark_scale:5000)
* A6 Highway, Italy (coord|44.320409|8.377118|type:landmark_region:IT_source:Google)

Many Multi-storey car parks feature such a design as this.

External links

* [http://www.steamlocomotive.com/model/trackage.shtml Helixes, Tunnels, Spirals, and Other Unique Trackage]

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