According to Wikipaedia:

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.[citation needed] 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.

The modern electric traffic light is an American invention.[1] As early as 1912 in Salt Lake City, Utah, policeman Lester Wire invented 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 East 105th Street and Euclid Avenue in Cleveland, Ohio.[2][3] It had two colors, red and green, and a buzzer, based on the design of James Hoge, to provide a warning for color changes. The design by James Hoge[4] allowed police and fire stations to control the signals in case of emergency. The first four-way, three-colour traffic light was created by police officer William Potts in Detroit, Michigan in 1920.[5] In 1923, Garrett Morgan patented a traffic signal device. Ashville, Ohio claims to be the location of the oldest working traffic light in the United States, used at an intersection of public roads until 1982 when it was moved to a local museum.[6]

The first interconnected traffic signal system was installed in Salt Lake City in 1917, with six connected intersections controlled simultaneously from a manual switch. Automatic control of interconnected traffic lights was introduced March 1922 in Houston, Texas.[7] The first automatic experimental traffic lights in England were deployed in Wolverhampton in 1927.[8]