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.
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.
List of spirals
Argentina Two spirals between Tacuara and Meseta at and on the heritage Tren a las Nubes section of the Salta–Antofagasta railway part of the General Manuel Belgrano Railway.
Australia Spiral on the uphill track at Bethungra on the Main Southern railway line in New South Wales. The downhill track remains on the original steep plain 1 in 40 gradient. Spiral on the single track at Cougal on the North Coast railway line, New South Wales.
Bulgaria Four Spirals on the Rhodope Mountain Line between Septemvri to Dobrinishte railway between Velingrad and Cherna Mesta at , , and . Spiral just outside Klisura at on the Sofia to Tulovo railway. Spiral just outside Radevtsi at on the Ruse to Dimitrovgrad railway. Spiral and horseshoe bends just outside Raduntsi at on the Ruse to Dimitrovgrad railway.
Canada Double spiral at Big Hill at on the approach to Kicking Horse Pass on the Canadian Pacific Railway route. There used to be a spiral at at Trinity, Newfoundland on the former Newfoundland Railway. There used to be a spiral at Rogers Pass at that was superseded when the Connaught Tunnel (British Columbia) was built.
China
There used to be a spiral at Guanjiao at on the Qinghai–Tibet Railway; it was replaced by a tunnel in 2014. (see photo). Spiral between Qingshiya and Guanyinshan at on the Baoji–Chengdu Railway. Six spirals on the Chengdu–Kunming Railway at: South of Baishiyan at . Lewu at . Wazu at . Tiekou at . Ananzhuang at . Longgudian at . Spiral at Shangshali at on the Harbin–Manzhouli Railway. Spiral at Daheba at on the Sichuan–Guizhou railway. Three spirals on the Liupanshui–Hongguo Railway at: Maocaoping at . Duchuanzhai at . Sanjiazhai at . There are four spirals on the Southern Xinjiang Railway at , , and on a by-passed section between Yu'ergou and Hejing that is now freight only. This line was rebuilt on a shorter route in 2014.
Costa Rica Replica of the Brusio Spiral Viaduct at on the Tren Turistico Arenal, 10 km east of Nuevo Arenal, Guanacaste.
Croatia Spiral between Rijeka-Brajdica and Sušak-Pećine at on the Rijeka–Karlovac railway, part of International corridor V. The spiral is mainly in a tunnel.
Eritrea Spiral between Asmara and Arbaroba at on Eritrean Railways. This spiral pushes the definition of a spiral as the line crosses itself but then immediately crosses back, and it does this in a tunnel.
France Three spirals on the Col de Tende line between Ventimiglia to Cuneo as it passes through France, a further spiral on this line is in Italy. Just north of Fontan at . Saint Dalmas-de-Tende at . Tende at . Spiral at Moûtiers at between Albertville and Bourg-Saint-Maurice used by TGV. Spiral partly in a tunnel at Claveisolles at on the Paray-le-Monial to Lozanne line (between Saint-Nizier-d'Azergues and Poule-les-Écharmeaux). Spiral north of L'Hospitalet près l'Andorre at on the line between Latour-de-Carol and Ax-les-Thermes. There used to be a spiral in the Sayerce tunnel at on the former Pau–Canfranc railway line between Pau and Zaragoza (Spain) in the Pyrenees. This spiral is now a footpath. The proposed spirals between The Gravenne and Montpezat at on the partly completed Transcevenole line between Le Puy-en-Velay and Lalevade-d'Ardèche in the Cévennes were never constructed.
Germany Spiral, known as the Rendsburg Loop, on the northern approach to the Rendsburg High Bridge, a railway viaduct and transporter bridge crossing the Kiel Canal in Rendsburg, Schleswig-Holstein at . Spiral on the Wutach Valley Railway at . The line was built partly for strategic reasons and had to be built to a reasonable gradient in order to haul heavy military trains over it. The alternative, shorter Singen–Waldshut route was not available for this traffic, since it crossed Swiss territory. The line is now a heritage railway.
India
There are currently three spirals on the Darjeeling Himalayan Railway: Chunbati Loop at . Agony Point at . Batasia Loop at . 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. There used to be a spiral at Dhulghat at between Khandwa and Hingoli on the metre gauge railway, the spiral was apparently removed when the track was upgraded to broad gauge.
Iran Spirals near Dowgal station at and extensive horseshoe curves in the Alborz Mountains on the Trans-Iranian Railway.
Ireland The St. James's Gate Brewery, Dublin, Ireland formerly had an internal gauge railway with a loop in a tunnel to gain height between buildings.
Italy Spiral at Bortigiadas on the Sassari-Palau railway on Sardinia. Spiral near Lanusei on the Mandas–Gairo–Arbatax railway on Sardinia. Varzo Spiral Tunnel near Iselle di Trasquera on the Swiss Federal Railways just south of the Southern Portal of the Simplon Tunnel. Spiral near Vernante on the Col de Tende railway from Ventimiglia to Cuneo. There are a further three spirals on this line in French territory. Spiral close to Savona at on the Savona–Altare line. Spiral just north of Salerno at on the Salerno–Mercato San Severino railway. Spiral at Ragusa at on the approach to Ragusa from Modica on Sicily. Spiral between Medaglie d'Oro and Salvator Rosa at on Line 1 of Naples Metro. Vanvitelli and Quattro Giornale stations are on the loop itself. Spiral at Casole Bruzio on the Cosenza to San Giovanni in Fiore line (line exists but is not in service). There were three spirals at Caprareccia and and near San Martino on the former Spoleto–Norcia line.
Japan
Spiral South of Echigo-Nakazato at on the Tokyo bound Jōetsu Line. Spiral at Shimizu Tunnel at on the Tokyo-bound Jōetsu Line. Spiral South of Tsuruga Station at on the Hokuriku Main Line to Shin-Hikida Station. Spiral at Okoba Station at on the Hisatsu Line. Okoba Station is situated on a zig zag part way around the loop. Spiral on the Nakamura Line just after its junction with the Yodo Line at . Spiral on the western approach to the Rainbow Bridge at on New Transit Yurikamome automated transit service in Tokyo.
Kenya
There are three spirals on the gauge railway line from Kenya to Uganda. This railway has been superseded by the Mombasa–Nairobi Standard Gauge Railway, which has removed the need for spirals by constructing tunnels and bridges.
Spiral South of Mazeras at near Mombasa. Spiral near Makutano station at : . Spiral near Equator station at . Madagascar Spiral at Anjiro at on the main line from Antananarivo to Toamasina.
Mexico Spiral between Creel and San Rafael at on the Ferrocarril Chihuahua al Pacífico.
Myanmar
One spiral on the Burma Mines Railway at . One spiral close to Shwenyaung at on the Thazi-Taunggyi line.
New Zealand Raurimu Spiral at on the North Island Main Trunk. The line is single track and involves two short tunnels around a suitable hill. Spiral on the Driving Creek Railway at . This railway also has several reverses or zig-zags. There used to be a spiral at on the Ellis and Burnand Tramway, Ongarue, which closed in 1958 and is now part of the Timber Trail.
Norway Spiral on the Flåm Line between Myrdal and Flåm at . Spiral on the Vestfold Line around the town of Tønsberg at .Sigurd H. Unneberg, Sem og Slagen, en bygdebok Bind 2, Kulturhistorie, del 2 . Tønsberg: Høgskolen i Vestfold, 2001. Relevant chapter is online here
Peru Spiral between San Bartolome and Matucana at on the Central Railway.
Russia Spiral just north of Indyuk at on the North Caucasus Railway route from Tuapse (Tуапсе) through Gornyy to Belorechensk (Белореченск). There used to be a spiral at "Devil's Bridge", on the now abandoned line from Kholmsk to Yushno-Sakhalinsk on Sakhalin Island.
Serbia Spiral at Jatare at on the Šargan Eight Heritage Railway in Western Serbia between from Mokra Gora and Šargan Vitasi.
Slovakia Spiral at Telgártska slučka at on the Brezno to Gelnica Line. The spiral is constructed of two viaducts and a tunnel.
South Africa Spiral near Komga at on the branch line to Mthatha as it descends to the Great Kei River. Spiral at Van Reenen's Pass at on the line from Harrismith to Ladysmith.
South Korea
Spiral at Hambaek 1st Tunnel at between Hambaek station and Jodong station on the Hambaek Line;– one loop, single track. Spiral at Solan Tunnel at between East Baeksan station and Dogye station on the Yeongdong Line. There is one loop on a single track railway but double track is installed in the middle of the tunnel to enable trains from opposing directions to pass each other. There used to be a spiral at Daegang Tunnel at between Danseong station and Jungnyeong station on the Jungang Line;– one loop, single track. A new double track tunnel has opened which by-passes the line with the spiral, which has since closed. There used to be a spiral at Ddwari Tunnel at between Geumgyo station and Chiak station on Jungang Line. A new double track tunnel has opened which by-passes the line with the spiral, which has since closed.
Spain Spiral near Toses at on the Ripoll to Latour-de-Carol, France line. Spiral at La Granja de San Vicente at on the Palencia to A Coruña line.
Sri Lanka Spiral at Demodara railway station at on the line from Bandarawela to Badulla. Demodara railway station is located above the spiral tunnel.
Switzerland
The Gotthard railway has spirals and horseshoe curves or bends mostly in tunnels on its standard gauge, double track line. The spirals are: North of Wassen at Pfaffensprung on the Northern approach at , this loop is followed by two horseshoe bends around Wassen. Piottino spirals on the Southern approach at and at . Biaschina double spiral near Anzonico at . RhB Albulabahn has four spirals, mainly in tunnels, on its metre gauge single track. The spirals are at: Filisur at . South of Bergün at . Double spiral North of Preda at . It could also be argued that the horseshoe curves immediately South of Bergün at also form a spiral as it appears that one curve overlaps the other. Brusio spiral viaduct at on RhB Berninabahn. This is a fine example of an open spiral mainly on the Brusio spiral viaduct on a metre gauge single track railway. Spiral South of Gletsch at on the former Furka Oberalp Bahn, now Dampfbahn Furka-Bergstrecke Heritage Railway. This is a single track partial rack railway with the catenary equipment removed. Spiral East of Grengiols at on the former Furka Oberalp Bahn, now Matterhorn Gotthard Bahn, between Grengiols and Lax.
Taiwan
Triple spiral (with long sections in tunnels) at Dulishan at on the Alishan Forest Railway. Track length is 5 kilometers, while the endpoints of the spiral are only 570 meters apart horizontally and 233 meters vertically.
Uganda There used to be a spiral at Circle Hill on the Western Uganda Extension of the Kenya to Uganda Railway Line to Kasese.
United Kingdom
Spiral around Dduallt railway station at on the Ffestiniog Railway in Wales. The line at 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