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NYC Subway Signals: A Complete Guide (2012)
cument également disponible en français All divisions of the New York City subway use what is now called "wayside color-light block signalling", that is, signals are physically located to the side of the track (as opposed to being overhead, or transmitted directly to the train), utilize the colors of lights (as opposed to semaphores or other devices, or positions or shapes of lights), and rely on dividing tracks into discrete blocks (or track sections or track circuits) to electrically detect the presence of trains. Nearly all of the routes of the current subway are signalled with classic wayside block signalling, whose principles have not changed markedly since the opening of the IRT in 1904.
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