Turning loop

A balloon loop, turning loop or reversing loop (North American) allows a rail vehicle or train to reverse direction without having to shunt or even stop. Balloon loops can be useful for passenger trains and unit freight trains such as coal trains.

Balloon loops are common on tram or streetcar systems. Many streetcar and tram systems use single-ended vehicles that have doors on only one side and must be turned at each end of the route, or else haul trailer cars with no driver's cabin in the rear car.

Balloon loops were first introduced on metro and tram lines. They did not appear on freight railways in large numbers until the 1960s when the modernising British Rail introduced merry-go-round (MGR) coal trains that operated from mines to power stations and back again without shunting.

Balloon loops enable higher line capacity (faster turnaround of a larger number of trams) and also allow the use of single-ended trams which have several advantages, including lower cost and more seating when doors are on one side only. However, double-ended trams also benefit from the capacity advantage of balloon loops, for example on the former Sydney tram system where loops were used from 1881 until the system's closure in 1961. Initially the Sydney system was operated by single-ended steam trams and then, from the 1890s, by double-ended electric trams. Lines were looped in the Sydney CBD and the other busiest areas of operation, such as the La Perouse, New South Wales and other eastern suburbs lines, as they provided greater turn-around capacity on this very busy system. The Sydney system was possibly the first major example of a looped tramway system. European systems were extensively converted to looped operation in the early twentieth century and most of them changed to single-ended trams. Looped operation with single-ended trams was also used on many North American streetcar systems.

On a balloon loop: the station is on the balloon loop, and the platform may be curved or straight.

Multiple stations on a balloon loop:

With balloon loop: The balloon loop is past the station.

Balloon loops are used extensively on tramway systems with single-ended trams. Usually located at termini, the loop may be a single one-way track round a block. Single-ended trams have a cab at only one end and doors on one side, making them cheaper and having more space for passengers. On tram systems with double-ended trams balloon loops are not required but may still be used as they can provide greater turn-around capacity than a stub terminus; the Birmingham Corporation Tramways terminus at Rednal had a balloon loop in addition to the conventional stub tracks, providing extra capacity to handle weekend and bank holiday crowds visiting the nearby Lickey Hills. The Milan interurban tramway network, although using double-ended trams, had balloon loops at termini within the city limits so that they could be used as backup termini by the single directional trams used on urban service. In Milan, tramway depots are built as balloon loops, just as urban termini. Another example is in Potsdam, Germany.

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Wikipedia