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Traffic light
Traffic lights, traffic signals, or stoplights – also known as robots in South Africa, Zambia, and Namibia – are signalling devices positioned at road intersections, pedestrian crossings, and other locations in order to control the flow of traffic.
Traffic lights usually consist of three signals, transmitting meaningful information to road users through colours and symbols, including arrows and bicycles. The usual traffic light colours are red to stop traffic, amber for traffic change, and green to allow traffic to proceed. These are arranged vertically or horizontally in that order. Although this is internationally standardised, variations in traffic light sequences and laws exist on national and local scales.
Traffic lights were first introduced in December 1868 on Parliament Square in London to reduce the need for police officers to control traffic. Since then, electricity and computerised control have advanced traffic light technology and increased intersection capacity. The system is also used for other purposes, including the control of pedestrian movements, variable lane control (such as tidal flow systems or smart motorways), and railway level crossings.
In December 1868, the first system of traffic signals, which was a semaphore traffic signal, was installed as a way to replace police officer control of vehicular traffic outside the Houses of Parliament in London, England. This system exploded on 2 January 1869 and was taken down. This early traffic signal led to other parts of the world implementing similar traffic signal systems. 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. These traffic signals were controlled by a traffic officer who changed the commands on the signal to direct traffic.
In 1912, the first electric traffic light was developed by Lester Wire, a policeman in Salt Lake City, Utah. In August 1914, it was installed by the American Traffic Signal Company on the corner of East 105th Street and Euclid Avenue in Cleveland, Ohio. In 1920, the first four-way, three-colour traffic light was created by William Potts in Detroit, Michigan. His design was the first to include an amber 'caution' light along with red and green lights. Potts was Superintendent of Signals for the Police Department of Detroit. In 1921, he installed automatic four-way, three-colour traffic lights in 15 towers across Detroit.
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. New York City was able to reassign all but 500 of its 6,000 officers working on the traffic squad, saving the city $12,500,000. In 1923, Garrett Morgan patented a design of a manually operated three-way traffic light with moving arms.
The control of traffic lights changed with the rise of computers in America in the 1950s. One of the best historical examples of computerised control of lights was in Denver, Colorado in 1952. In 1967, Toronto, Canada was the first to use more advanced computers that were better at vehicle detection. The computers maintained control over 159 signals in Toronto through telephone lines.
A set of lights, known as a signal head, may have one, two, three, or more aspects. The most common signal type has three aspects facing the oncoming traffic: red on top, amber (yellow) below, and green below that. Additional aspects may be fitted to the signal, usually to indicate specific restrictions or filter movements.
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Traffic light
Traffic lights, traffic signals, or stoplights – also known as robots in South Africa, Zambia, and Namibia – are signalling devices positioned at road intersections, pedestrian crossings, and other locations in order to control the flow of traffic.
Traffic lights usually consist of three signals, transmitting meaningful information to road users through colours and symbols, including arrows and bicycles. The usual traffic light colours are red to stop traffic, amber for traffic change, and green to allow traffic to proceed. These are arranged vertically or horizontally in that order. Although this is internationally standardised, variations in traffic light sequences and laws exist on national and local scales.
Traffic lights were first introduced in December 1868 on Parliament Square in London to reduce the need for police officers to control traffic. Since then, electricity and computerised control have advanced traffic light technology and increased intersection capacity. The system is also used for other purposes, including the control of pedestrian movements, variable lane control (such as tidal flow systems or smart motorways), and railway level crossings.
In December 1868, the first system of traffic signals, which was a semaphore traffic signal, was installed as a way to replace police officer control of vehicular traffic outside the Houses of Parliament in London, England. This system exploded on 2 January 1869 and was taken down. This early traffic signal led to other parts of the world implementing similar traffic signal systems. 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. These traffic signals were controlled by a traffic officer who changed the commands on the signal to direct traffic.
In 1912, the first electric traffic light was developed by Lester Wire, a policeman in Salt Lake City, Utah. In August 1914, it was installed by the American Traffic Signal Company on the corner of East 105th Street and Euclid Avenue in Cleveland, Ohio. In 1920, the first four-way, three-colour traffic light was created by William Potts in Detroit, Michigan. His design was the first to include an amber 'caution' light along with red and green lights. Potts was Superintendent of Signals for the Police Department of Detroit. In 1921, he installed automatic four-way, three-colour traffic lights in 15 towers across Detroit.
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. New York City was able to reassign all but 500 of its 6,000 officers working on the traffic squad, saving the city $12,500,000. In 1923, Garrett Morgan patented a design of a manually operated three-way traffic light with moving arms.
The control of traffic lights changed with the rise of computers in America in the 1950s. One of the best historical examples of computerised control of lights was in Denver, Colorado in 1952. In 1967, Toronto, Canada was the first to use more advanced computers that were better at vehicle detection. The computers maintained control over 159 signals in Toronto through telephone lines.
A set of lights, known as a signal head, may have one, two, three, or more aspects. The most common signal type has three aspects facing the oncoming traffic: red on top, amber (yellow) below, and green below that. Additional aspects may be fitted to the signal, usually to indicate specific restrictions or filter movements.