answer in English
- oscarchchungLv 41 decade agoFavorite Answer
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.
The modern electric traffic light is an American invention. 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 105th Street and Euclid Avenue in Cleveland, Ohio.  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 (USPTO # 1251666 Sept. 22, 1913) allowed Police and Fire stations to control the signals in case of emergency. The first four-way, three-color traffic light was created by police officer William Potts in Detroit in 1920. In 1923, Garrett Morgan patented a traffic signal device, although it was not a precursor of the modern traffic light .
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. The first automatic experimental traffic lights in England were deployed in Wolverhampton in 1927.
Ampelmännchen pedestrian traffic signals have come to be seen as a nostalgic sign for the former German Democratic Republic.
Traffic lights for vehicles or pedestrians normally have two main lights—a red light that means 'stop' and a green (or sometimes white for pedestrians) light that means 'go' (or, more correctly, 'proceed with caution'); the use of these colors are thought to originate from nautical right-of-way. Usually, the red light contains some orange in its hue, and the green light contains some blue, to provide some support for people with red-green color blindness. In most countries there is also a yellow (colloquial term) or amber(official term) light, which when on by itself and not flashing means stop if able to do so safely. In some systems, a flashing amber means that a motorist may go ahead with care if the road is clear, giving way to pedestrians and to other road vehicles that may have priority. A flashing red is treated as a regular stop sign.
There may be additional lights (usually a green arrow or "filter") to authorize turns. In the U.S., a turn permitted by such a light is called a protected left or protected right. A left turn light preceding the opposing through movement is called a leading left turn because it leads the opposing through green light (likewise, a left turn arrow that follows the opposing through movement is known as a lagging left turn). In Canada, a turn that is authorized before the opposing traffic is called an advanced green and a green arrow at the end of the phase is called a delayed green. A leading left turn, advanced green, lagging left, or delayed green can apply either to only one direction, allowing both turning and through traffic while opposing traffic is stopped, or to both directions, allowing left turns from opposing directions while all through traffic is stopped.Source(s): Wkipedia
- Anonymous1 decade ago