Operation
Although some railroads still rely on older, simpler electronic lighted displays and manual controls, in modern implementations, dispatchers rely on computerized systems similar to supervisory control and data acquisition (SCADA) systems to view the location of trains and the aspect, or display, of absolute signals. Typically, these control machines will prevent the dispatcher from giving two trains conflicting authority without needing to first have the command fail at the remote interlocking. Modern computer systems generally display a highly simplified mock-up of the track, displaying the locations of absolute signals and sidings. Track occupancy is displayed via bold or colored lines overlaying the track display, along with tags to identify the train (usually the number of the lead locomotive). Signals which the dispatcher can control are represented as either at Stop (typically red) or "displayed" (typically green). A displayed signal is one which is not displaying Stop and the exact aspect that the crew sees is not reported to the dispatcher.
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