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Subway Signal Design Has Old-School Origin


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Q. I’ve noticed that on my subway line, the rail signal lights are arranged so that the red light is on the bottom and the green light is on the top, which is the opposite of street traffic lights. Any special reason for this difference?


A. The answer comes in a brief history lesson from Antonio Cabrera, assistant chief officer for track engineering at New York City Transit:


Long before electric lights, railroads used wooden semaphore arms, which were patented in the 1840s. Fastened to a pole, they signaled their message to the train engineer based on their angle to the pole. If the arm was straight up, it meant the track was clear; if it stuck out horizontally, it meant “stop.”


Railroads then began to add colored disks to the opposite ends of the semaphore arm, illuminated by kerosene and then by electric lights. The disks were arranged so that when the semaphore arm was in the vertical position (“Clear”), the green disk was lighted; when the arm was in the horizontal position ( “Stop” ), the red disk was lighted.


“When semaphore arms disappeared and were substituted by electric lights, the relative position of the colored disks was kept,” Mr. Cabrera said in an e-mail message.

Read more: http://www.nytimes.com/2010/05/16/nyregion/16fyi.html

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So does this explain the design of the slightly demonic-looking 'vintage' signals currently found on the (7) line?


Well original IRT signals were like this:




This is different from the set up of semaphore signals.

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