Loop (rail)

In rail terminology, a loop can mean one of two configurations:

a stretch of rail track that provides a place for a train to halt temporarily while other trains pass on an adjacent main line . This configuration allows the sequence of trains along a track to change. The feature is common on single-track and busy double track railways throughout Britain and Ireland. In the US this sort of track is called a passing siding: in Britain, a passing loop or crossing loop, the former (passing loop) is used in Australia.
a railway line which describes a loop, or part thereof, sometimes allowing trains to return to the start point by a different route. Examples in England are the Dartford Loop in south east London and the Hounslow Loop in west London. The same term is used in Australia: examples there being the City Loop in Melbourne or the Ekka Loop in Brisbane. Sydney's underground system is known as the City Circle. Similarly, in US terminology, a loop is a section of track which curves back onto itself to allow trains to change direction, but often much smaller in extent. This is less common than a wye track. This kind of loop may be called a balloon loop or (at least in US model railroading parlance) a "reversing loop".

A spiral loop is a 360° turn used to gain height in a relative small space, used in railway construction in mountainous areas.

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