Railroad switch

A railroad switch (known in British and Australian English as (a set of) points or, in technical usage, a turnout) is a mechanical installation provided at a point where rail track 'A' (see illustration, right) divides into two tracks, 'B' and 'C'. Each switch contains a pair of linked tapering rails (point blades) that can be moved laterally into one of two positions, determining whether a train coming from 'A' will be led towards 'B' or towards 'C'. A train coming from 'B' or 'C' will be led to 'A' anyway if the moving parts of the switch are not locked (passage in this direction through a switch is known as a "trailing movement"). Given, however, the potential for derailment at all but the slowest speeds in thus "forcing" a switch, and the fact that the switch blades on all main running-lines are mechanically or electrically locked into position, it is normal to set switches in the appropriate position for trailing movements too. End 'A' is referred to as the facing-point end.

Related Topics:
British - Australian English - Rail track - Train - Derailment

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The position of the switch is usually changed electrically on main lines and controlled from a remote control center or signal box, from where staff also alter semaphores or light signals correspondingly. In rarely used sidings, low-traffic branch lines, self-contained marshalling yards or on heritage railways a switch might be manually operated with a points lever. The switch points of tram lines are often operated remotely by the driver. Prior to the widespread availability of electricity, switches at heavily traveled junctions were operated from a tower constructed near the tracks through an elaborate system of rods and levers.

Related Topics:
Signal box - Signals - Heritage railway - Tram - Driver - Electricity - Junctions - Tower - Levers

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With a right switch A and B form a straight track and C is to the right of B, with a left switch C is to the left. A switch may also be symmetric, or tracks AB and AC may be curved at different radii in the same or different directions.

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The correct setting of points is fundamental to the safe running of a railway. A fatal train accident at Potters Bar, Hertfordshire, UK occurred in May 2002, when a switch sprang to a different position as a coach crossed it. The front coach wheels therefore progressed from A to B whereas the rear wheels slewed towards C, causing the whole coach to detach from the train and slew sideways across the platform ahead. Thankfully the movement of the switch occurred beneath the final coach, so that although seven people were killed, the front coaches were spared. Poor maintenance of the points was held to be the primary cause of the crash. (Perhaps the greatest security challenge in railway operation is preventing the tampering of manually-operable switches: a similar wreck in Stewiacke, Nova Scotia, April 12, 2001 — luckily nonlethal — was caused by a switch being unlocked by "bored" teenagers.)

Related Topics:
Fatal train accident - Potters Bar - Hertfordshire - Platform - Stewiacke, Nova Scotia - April 12 - 2001

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Monorail systems have special switches, see the external link, a page which includes animations.

Related Topics:
Monorail - Animation

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