The New York City, NY, USA, Traffic Signal System - A Standards-Based Approach

HISTORY

The City of New York, NY, USA, has approximately 11,000 signalized intersections. Most of these intersections use single dial, electromechanical controllers, in which a simple timing dial controlled by a synchronous motor advances a load switching camshaft that provides one circuit for each signal and/or pedestrian display for each phase. The contacts ride on "cams" that are broken off to enable the power to the signal display.

The camshaft is ratcheted, or advanced, based on the position of "keys" located around the dial to provide the interval timing. The dial typically makes one revolution per cycle (gears select the cycle length). Interlocks ensure that the dial and cam remain in sync. A single offset key is used to set the relationship between intersections.