"On 10 December 1868, the first traffic lights were installed outside the British Houses of Parliament in London, by the railway engineer J.P. Knight. They resembled railway signals of the time, with semaphore arms and red and green gas lamps for night use. The gas lantern was turned with a lever at its base so that the appropriate light faced traffic. Unfortunately, it exploded on 2 January 1869, injuring the policeman who was operating it.
On Potsdamer Platz, Berlin Germany, it is widely claimed (though this is subject to some disagreement), that the world's first electric street lights were installed there in 1882. What is not refuted is that Europe's first traffic lights were erected there in 1924 in an attempt to control the sheer volume of traffic passing through. These lights were mounted on a five-sided 8.5 metre high tower, at the top of which a policeman sat in a small cabin and switched the lights manually, though they were automated after a few years (a replica of this tower was erected in the late 1990s close to its original location).
The modern electric traffic light is an American invention.<4> As early as 1912 in Salt Lake City, Utah, policeman Lester Wire set up the first red-green electric traffic lights. On 5 August 1914, the American Traffic Signal Company installed a traffic signal system on the corner of 105th Street and Euclid Avenue in Cleveland, Ohio. Based on the design of James Hoge, it had two colors, red and green, and a buzzer to provide a warning for color changes. The first four-way, three-color traffic light was created by police officer William Potts in Detroit in 1920.<1> In 1923, Garrett Morgan patented a traffic signal device, although it did not directly impact the evolution of the modern traffic light <5>."
http://en.wikipedia.org/wiki/Traffic_light
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