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(last edited July 20, 2005) Front Page | Recent Changes | Title Index | User Preferences | Random Page | HelpMeans by which the passage of trains is detected and the information used to control signals provided for train safety and control. The simple track circuit consists of a relay energised by a low voltage circuit fed through the running rails of a section of track. Each section is electrically isolated from others. The energised relay detects no train present and can be used to switch power to a green signal light. If a train enters the section, its wheelsets will short out the circuit, causing the relay to de-energise and switch off the green signal. The relay will now switch on the red signal light. The light remains red until the last wheelset of the train clears the section, allowing the track circuit to be restored and the signal to return to green.
