The Turntable

In rail terminology, a railway turntable is a device for turning railway rolling stock, usually locomotives, so that they can be moved back in the direction from which they came. As steam locomotives replaced horses as the preferred means of power, they became optimised to run in only one direction for operational ease and to provide some weather protection. Railways needed a way to turn the locomotives around for return trips as their controls were often not configured for extended periods of running in reverse and in many locomotives the top speed was lower in reverse motion.


Triple gauge turntable, Peterborough, SA

In the case of diesel locomotives, though most can be operated in either direction, they are treated as having "front ends" and "rear ends" (often determined by reference to the location of the crew cab). When operated as part of a multiple unit locomotive consist, the locomotives can be arranged so that the consist can be operated "front end first" no matter which direction the consist is pointed. Turntables were also used to turn observation cars so that their windowed lounge ends faced toward the rear of the train.

Most turntables consist of a circular pit in which a steel bridge is rotated. The bridge is typically supported and balanced by the central pivot, to reduce the total load on the pivot and to allow easy turning. This is most often achieved by a steel rail running around the floor of the pit that supports the ends of the bridge when a locomotive entered or exited. Turntables have a positive locking mechanism to prevent undesired rotation and to align the bridge rails with the exit track. Rotation of the bridge can be accomplished manually (either by brute force or with a windlass system), popularly called an "Armstrong" turntable, by an external power source, or by the braking system of the locomotive itself, though this requires a locomotive to be on the table for it to be rotated.


Turntable, Tyseley Locomotive Works, Birmingham, England

The turntable bridge (the part of the turntable that includes the tracks and that swivels to turn the equipment) can span up to 36.6 metres (120 ft), depending on the railway's needs. Larger turntables were installed in maintenance facilities for longer locomotives, while short line and narrow gauge railways typically used smaller turntables. 18.3 metres (60 ft) is the most common size found in Australia's smaller regional railway yards with turntables above 24.4 metres (80 ft) in railway yards of bigger towns. Turntables as small as 1.83 metres (6 ft) in diameter have been installed in some industrial facilities where pieces of equipment are small enough to be pushed one at a time by humans or horsepower.

In engine maintenance facilities, a turntable is usually surrounded, in part or in whole, by a roundhouse. It is more common for the roundhouse to only cover a portion of the land around a turntable, but fully circular roundhouses do exist.

Australian Towns and Their Railway Stations

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to how railways work