Traffic light  

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"Even the walker’s freedom is now greatly restricted. In the city he continually has to stop to wait for traffic lights that are designed mainly to serve auto traffic."--"Unabomber Manifesto" (1995) by Ted Kaczynski

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Traffic lights, traffic signals, stoplights or robots (as they are known in South Africa) are signalling devices positioned at road intersections, pedestrian crossings, and other locations to control flows of traffic.


The first system of traffic signals was installed as a way to replace police officer control of vehicular traffic outside the Houses of Parliament in London on 9 December 1868. In the first two decades of the 20th century, semaphore traffic signals like the one in London were in use all over the United States with each state having its own design of the device. In many cases, it was controlled by a traffic officer who would blow a whistle before changing the commands on this signal to help alert travellers of the change.

In 1912, the first electric traffic light was developed by Lester Wire, a policeman in Salt Lake City, Utah. It was installed by the American Traffic Signal Company on the corner of East 105th Street and Euclid Avenue in Cleveland, Ohio. The first four-way, three-colour traffic light was created by William Potts in Detroit, Michigan in 1920. Potts was Superintendent of Signals for the Police Department of Detroit. He installed automatic four-way, three-colour traffic lights in 15 towers across Detroit in 1921. By 1922 traffic towers were beginning to be controlled by automatic timers more widely. The main advantage of the use of the timer was that it saved cities money by replacing traffic officers. The city of New York was able to reassign all but 500 of its 6,000 officers working on the traffic squad; this saved the city $12,500,000.

Garrett Morgan received a patent for the design of another type of three-way traffic light in 1923.

The control of traffic lights made a big turn with the rise of computers in America in the 1950s. One of the best historical examples of computerized control of lights was in Denver in 1952. In 1967, the city of Toronto was the first to use more advanced computers that were better at vehicle detection. The computers maintained control over 159 signals in the cities through telephone lines.

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Unless indicated otherwise, the text in this article is either based on Wikipedia article "Traffic light" or another language Wikipedia page thereof used under the terms of the GNU Free Documentation License; or on research by Jahsonic. See Art and Popular Culture's copyright notice.

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