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

Australia

Bulgaria

Canada

China

Costa Rica

Replica of the Brusio Spiral Viaduct at 10.479°N, -84.82374°W on the Tren Turistico Arenal, 10 km east of Nuevo Arenal, Guanacaste.

Croatia

Eritrea

France

Germany

India

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.

Iran

Ireland

Italy

Japan

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 This railway has been superseded by the Mombasa–Nairobi Standard Gauge Railway, which has removed the need for spirals by constructing tunnels and bridges.

Madagascar

Mexico

Myanmar

New Zealand

Norway

Peru

Russia

Serbia

Slovakia

South Africa

South Korea

Spain

Sri Lanka

Switzerland

Taiwan

Uganda

United Kingdom

United States