From “Just What is a Train Dispatcher?” Copyright © 1992 Thomas A. White

The traffic handled by air traffic control, except in runway and taxiway situations, consists only of the airplanes themselves. The train dispatcher’s traffic consists not only of the trains, but also all track maintenance. Unlike runways and taxiways, track maintenance is usually done under traffic and the same standards apply to track maintenance as apply to the movement of trains. The technical collision occurs at the moment that conflicting instructions are issued. Even if detected and corrected immediately, a conflict was created that is not allowed at all. Once the instructions are issued, there is even less chance of changing them to prevent a collision than there is when two trains are involved. In addition to the difficulties inherent to ground-to-ground radio communication, track maintenance work is noisy and may also involve working at considerable distance from all but a short-range portable radio. Unlike runway or taxiway maintenance which is done within sight of the controller, track maintenance is even more conceptual to the train dispatcher than is train traffic. The whereabouts of track maintenance workers is not regularly reported to the dispatcher as is train traffic and even in areas where train dispatchers handle traffic by the use of controlled signals and visual displays, the track maintenance work usually is not represented automatically as is train traffic, but must be added to the display manually by the dispatcher. Just an error in adding the representation of track maintenance to the display, be it placed in the wrong location or completely overlooked, is in itself a hazard of collision only one minute step from the actual issue of conflicting instructions which occurs when a signal is cleared for the movement of a train because it was not prevented by that manually-placed representation of track maintenance work.

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