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A right-hand railroad switch with point indicator pointing to right Animated diagram of a right-hand railroad switch. Rail track A divides into two: track B (the straight track) and track C (the diverging track); note that the green line represents direction of travel only, the black lines represent fixed portions of track, and the red lines depict the moving components.
Signal types. North American signals are commonly of three types. Absolute – Absolute signals are usually connected to an interlocking controlled by a block operator or train dispatcher. Their most restrictive aspect is "stop" and trains cannot pass them at stop unless they obtain special authority.
On a rail transport system, signalling control is the process by which control is exercised over train movements by way of railway signals and block systems to ensure that trains operate safely, over the correct route and to the proper timetable. Signalling control was originally exercised via a decentralised network of control points that were ...
An interlocking system is designed so that it is impossible to display a signal to proceed unless the route to be used is proven safe. Interlocking is a safety measure designed to prevent signals and points/switches from being changed in an improper sequence. For example, interlocking would prevent a signal from being changed to indicate a ...
Union Switch & Signal (commonly referred to as US&S) was an American company based in Pittsburgh, Pennsylvania, which focused on railway signaling equipment, systems and services. The company was acquired by Ansaldo STS (from 2015, Hitachi Rail STS ) in 1988, [ 1 ] operating as a wholly-owned company until January 2009, when US&S was renamed ...
North American railroad signaling. Standards for North American railroad signaling in the United States are issued by the Association of American Railroads (AAR), which is a trade association of the railroads of Canada, the US, and Mexico. Their system is loosely based on practices developed in the United Kingdom during the early years of ...
Railway signalling. A Class 66 locomotive (right) is waiting at a red signal while a First Great Western (now Great Western Railway) passenger train (left) crosses its path at a junction. Railway signalling (BE), or railroad signaling (AE), is a system used to control the movement of railway traffic. Trains move on fixed rails, making them ...
Automatic block signaling. Automatic block signaling (ABS), spelled automatic block signalling or called track circuit block (TCB[1]) in the UK, is a railroad communications system that consists of a series of signals that divide a railway line into a series of sections, called blocks. The system controls the movement of trains between the ...