LOOP (RAIL)

In rail terminology, a 'loop' can mean the following:

★ Passing loop/crossing loop (Commonwealth) or passing siding (US), a place for a train to wait while other trains pass on an adjacent main line.

★ Loop line (rail) or simply "loop" (UK), a railway line which describes a loop, or part thereof, allowing trains to return to the start point by a different route.
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★ Dartford Loop in south east London, England
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★ Hounslow Loop in west London.
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★ City Loop, in Melbourne, Australia
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★ Ekka Loop in Brisbane, Australia
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★ City Circle, the portion of Sydney, Australia's commuter railway system under the CBD
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★ The Loop—the hub of Chicago's 'L' rapid transit system

★ Balloon loop or simply "loop" (US), a section of track which curves back onto itself to allow trains to change direction, less common than a wye (Commonwealth: triangle) track. Also known in US model railroading parlance as a "reversing loop".

★ Spiral loop, a 360° turn used to gain height in a relative small space, used in railway construction in mountainous areas.