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 There used to be a spiral at Rogers Pass at that was superseded when the Connaught Tunnel (British Columbia) was built.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 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 .