The first traffic light was set up at the junction of Bridge Street and Palace Yard in London, England on December 10, 1868. It was a gas-light mounted at the top of a 23-footsteel pole. One side was red and the other green, and a lever system made it rotate. Red meant "Stop", and green meant "Be careful." The light proved dangerous - a policeman was badly injured when it exploded as he was turning it.
The first electric traffic light was set up at Alfred A. Benesch's insistence at the junction of 105th Street and Euclid Avenue in Cleveland, Ohio on August 5, 1914. The manufacturer, the Traffic Signal Co. of Cleveland, had fitted the light with a bell that rang when the color changed. The first three-color traffic light was installed in New York City in 1918. (Inventions and Discoveries)