Spiral (railway)
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A spiral is a technique employed by railways to ascend steep hills.
Spiral viaduct of the Bernina Express near Brusio, Switzerland.
Guanjiao Spiral on Qinghai–Tibet Railway at night. The route containing the spiral was replaced by a 32-km long tunnel (at the time of completion the longest in China) in 2014.
Loop (Agony Point) on the DHR, India
Okoba spiral and zig zag in Hisatsu Line, Japan
Zig zag (railway)
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A railway zig zag or switchback is a railway operation in which a train is required to switch its direction of travel in order to continue its journey. While this may be required purely from an operations standpoint, it is also ideal for climbing steep gradients with minimal need for tunnels and heavy earthworks. For a short distance, the direction of travel is reversed, before the original direction is resumed. Some switchbacks do not come in pairs, and the train may then need to travel backwards for a considerable distance.
Australia: the Lithgow Zig Zag
Germany: zig zag required to cross the outer dyke on the railway serving the island of Nordstrandischmoor
Italy: zig zag on the Cecina-Volterra railway
Japan: Obasute Station platform sign displaying the switchback