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 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 centripetal acceleration experienced by a railroad vehicle and the passengers in the vehicle approaching the horizontal circular curve and to prevent abrupt forces and discomfort. These curves are also used in highway engineering.
A similar feature to railway spirals in road design is the pigtail bridge.
Calculations
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
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Africa
Argentina
Australia
- 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
Bulgaria
- Avramovo 760 mm (2 ft 57⁄8 in) gauge
- Klisura - 3rd main railway line, the spiral is built around the town
- Plachkovtsi - 4th main railway line
Canada
- Spiral tunnels between Field, BC, and the summit of Kicking Horse Pass, Canadian Pacific Railway. 51°26′10″N 116°24′13″W / 51.435976°N 116.403653°W
- Yoho spirals [1]
China
Croatia
- Tunnel 1838 m long (0+525 - 2+363) between Rijeka-Brajdica and Sušak-Pećine stations on the southern approach to the Rijeka-Karlovac railway, part of International corridor V.
France
- Sayerce tunnel between Pau and Zaragossa (Spain) in the Pyrenees [1]
- Nice-Cuneo (Italy), three spirals.
- Moûtiers, between Albertville and Bourg-Saint-Maurice (Savoie), (45°29′08″N 6°32′26″E / 45.485628°N 6.540444°E) used by TGV.
Germany
- Rendsburg Viaduct, southern approach. Unique oblong single loop onto the transporter bridge crossing the Kiel Canal
- The Wutach Valley Railway had to be built less steep than possible to haul heavy military trains over it, since it bypassed for the shorter Singen–Waldshut route crossing Swiss territory.
India
- Darjeeling Himalayan Railway (DHR) has three (originally five) loops, of which one is a double spiral. 2 ft (610 mm) gauge
Iran
- Numerous spirals through very mountainous regions, mostly entirely in tunnel and single track, eg the Three Golden Lines.
Ireland
- 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 [2]
Italy
- At Iselle di Trasquera on the SBB.
Japan
- Jōetsu 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
Madagascar
- One loop at Anjiro on the main line from Antananarivo to Toamasina.
Myanmar
- Two spirals on the Burmah Mines Railway [3]
New Zealand
- Raurimu Spiral on the North Island Main Trunk, single track, suitable hill, two short tunnels. See Map and Photo.
- Driving Creek Railway
Norway
Russia
- Loop (Petlevoy) Tunnels - 3 tunnels in Caucasus Mountains.
Slovakia
- Telgart Loop (Telgártska slučka - Slovak language)
South Korea
- Geumgyo 1st Tunnel - between Geumgyo station and Chiak station on Jungang Line - one loop, single track. New double track tunnel is under construction to replace loop tunnel.
- Daegang Tunnel - between Danseong station and Jungnyeong station on the Jungang Line - one loop, single track.
- Hambaek 1st Tunnel - between Hambaek station and Jodong station on the Hambaek Line - one loop, single track.
- Solan Tunnel - between East Baeksan station and Dogye station on the Yeongdong Line - one loop, single track but double track is installed on the middle of the tunnel; for both trains crossing each other. It will be opened in 2009.
Spain
- Cargol Tunnel on the Ripoll - La Tour de Carol (France) line
Sri Lanka
Switzerland
- 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
Taiwan
- 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, 1 ft 111⁄2 in (597 mm) 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 - 3 ft (914 mm) gauge (abandoned after fire, trestles still partly standing)
- Tenessee, Hiwassee Loop, in which the track wraps around a hill twice and crosses over itself on an 80-foot tall trestle.
- Colorado, Georgetown Loop
- Ophir Loop - Rio Grande Southern Railroad - 3 ft (914 mm) gauge (abandoned)
Spirals are not generally needed on tramways (street running or reserved track) or light rail lines because trams traditionally have all wheels powered, giving the ability to climb much steeper direct gradients than railways.
Roads
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, Spain39°49′55″N 2°48′57″E / 39.831968°N 2.81574°E
- New Clear Water Bay Road, New Kowloon, Hong Kong (22°19′54″N 114°13′29″E / 22.331717°N 114.224617°E
- N8 Bypass Brienzwiler, Switzerland (46°45′02″N 8°06′32″E / 46.750521°N 8.108833°E)
- Isenfluh, Switzerland.
- A6 Highway, Italy (44°19′13″N 8°22′38″E / 44.320409°N 8.377118°E)
Many Multi-storey car parks feature such a design as this.
References
External links
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