NYC Subway Signals: A Complete Guide

Summary

Ce document 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. (In-cab signalling and recent position- and radio-based technologies are slowly being deployed on some lines; the first to be cut over is the "L", chosen because it shares no trackage with other routes, and has a relatively simple service pattern, i.e. no express service.) Tracks are divided into track circuits (or sections, or blocks), normally hundreds of feet long, by insulated joints in the rails. Trains' wheels and axles short-circuit the two rails to indicate their presence in a block. While every signal occurs at an insulated joint (a block boundary), not every joint has a signal at it. Each block can either be occupied (any portion of a train in any part of it) or vacant (no train anywhere) at any time. Every signal has a control length, defined as the distance, a number of whole blocks beyond the signal (i.e., in the direction of traffic governed by it), whose occupancy forces the signal to red ("stop") - the control length of a signal enforces that separation between trains. A signal being clear (green or yellow) attests that there are no trains, or parts of trains, or other obstructions anywhere in its control length, that is, that its control length is clear of dangers. The New York City subway relies on automatic train stops to "trip" noncompliant trains, tha...