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.:*Dartford Loop in south east London, England.:*Hounslow Loop in west London.:*Liverpool Loop, in Liverpool, England. :*City Loop, in Melbourne, Australia:*Ekka Loop in Brisbane, Australia.:*City Circle, the portion of Sydney, Australia's commuter railway system under the CBD. :*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.