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Traffic lights, also known as traffic signals, traffic lamps, traffic semaphore, signal lights, stop lights, and (in technical parlance) traffic control signals,〔(Sites.Tufts.edu ) The Origins and Globalization of Traffic Control Signals — Retrieved 08 December 2013〕 are signalling devices positioned at road intersections, pedestrian crossings, and other locations to control conflicting flows of traffic. The world's first, manually operated gas-lit traffic signal was short lived. Installed in London in December 1868, it exploded less than a month later, killing its policeman operator. The first safe, automatic electric traffic lights were installed in the United States in the late 1890s.〔(Anticiperende netwerkregelingen ). (PDF)〕 Traffic lights alternate the right of way accorded to road users by displaying lights of a standard color (red, yellow, and green) following a universal color code. In the typical sequence of color phases: * The green light allows traffic to proceed in the direction denoted, if it is safe to do so and there is room on the other side of the intersection. * The yellow (or amber) light warns that the signal is about to change to red. In a number of countries – among them the United Kingdom – a phase during which red and amber are displayed together indicates that the signal is about to change to green.〔(【引用サイトリンク】title=Traffic Lights Sequence )〕 Actions required by drivers on an amber light vary, with some jurisdictions requiring drivers to stop if it is safe to do so, and others allowing drivers to go through the intersection if safe to do so. * A flashing yellow indication is a warning signal. In the United Kingdom, a flashing amber light is used only at pelican crossings, in place of the combined red–amber signal, and indicates that drivers may pass if no pedestrians are on the crossing. * The red signal prohibits any traffic from proceeding. * A flashing red indication is treated as a stop sign. In some countries traffic signals will go into a flashing mode if the controller detects a problem, such as a program that tries to display green lights to conflicting traffic. The signal may display flashing yellow to the main road and flashing red to the side road, or flashing red in all directions. Flashing operation can also be used during times of day when traffic is light, such as late at night. == History == . On 9 December 1868,〔City of Westminster blue plaque on the site〕 the first, non-electric, gas-lit traffic lights were installed outside the Houses of Parliament in London to control the traffic in Bridge Street, Great George Street and Parliament Street. They were promoted by the railway engineer J. P. Knight and constructed by the railway signal engineers of Saxby & Farmer. The design combined three semaphore arms with red and green gas lamps for night-time use, on a pillar, operated by a police constable. The gas lantern was manually turned by a traffic police officer, with a lever at its base so that the appropriate light faced traffic. Although it was said to be successful at controlling traffic, its operational life was brief. It exploded on 2 January 1869, as a result of a leak in one of the gas lines underneath the sidewalk,〔"(Westminster Street Semaphore Signals.-Gas. )" ''Times'' (England ) 6 Jan. 1869: 10. The Times Digital Archive. Web. 5 Aug. 2015. Describes the explosion but does not mention the fate of the policeman.〕 injuring or killing the policeman who was operating it. With doubts about its safety, the concept was abandoned until electric signals became available. The first electric traffic light was developed in 1912 by Lester Wire, a policeman in Salt Lake City, Utah, who also used red-green 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. 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〔(【引用サイトリンク】title=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, Michigan in 1920. Ashville, Ohio claims to be the home of the oldest working traffic light in the United States, used at an intersection of public roads from 1932 to 1982 when it was moved to a local museum.〔(Neato Stuff At the Ashville Museum ). ''Ashville Area Heritage Society''. Retrieved 2008-04-16.〕〔(World's Oldest Traffic Light ). ''RoadsideAmerica.com''. Retrieved 2014-02-11.〕 Many pictures of historical traffic lights appear at a Traffic Signal Trivia page.〔("Traffic Signal Trivia" )〕 Los Angeles installed its first automated traffic signals in October 1920 at five locations on Broadway. These early signals, manufactured by the Acme Traffic Signal Co., paired “Stop” and “Go” semaphore arms with small red and green lights. Bells played the role of today's amber or yellow lights, ringing when the flags changed—a process that took five seconds. By 1923 the city had installed 31 Acme traffic control devices.〔(CityDig: Should I Stop or Should I Go? Early Traffic Signals in Los Angeles ). ''Los Angeles Magazine''. Retrieved 2015-01-01.〕 The Acme semaphore traffic lights were often used in Warner Bros. Looney Tunes and Merrie Melodies cartoons for comedic effect due to their loud bell. 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.〔Section 1.5: "System Evolution", ''(Traffic Control Systems Handbook )'', Federal Highway Administration Report FHWA-HOP-06-006, October 2005.〕 The first traffic lights in Britain were deployed in Piccadilly Circus in 1926. Outside of London, Wolverhampton was the first British town to introduce automated traffic lights in 1927 in Princes Square at the junction of Lichfield Street and Princess Street.〔(【引用サイトリンク】title=Traffic Control and Traffic Signals )〕 Melbourne was the first city in Australia to install traffic lights in 1928 on the intersection of Collins and Swanston Street. Toronto, Ontario was the first city to computerize its entire traffic signal system, which it accomplished in 1963. Countdown timers on traffic lights were introduced in the 1990s. Timers are useful for pedestrians, to plan whether there is enough time to cross the intersection before the end of the walk phase, and for drivers, to know the amount of time before the light turns green. In the United States, timers for vehicle traffic are prohibited, but pedestrian timers are now required on new or upgraded signals on wider roadways. == Types and placement of colors== (詳細はウィキペディア（Wikipedia）』 ■ウィキペディアで「traffic light」の詳細全文を読む スポンサード リンク
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