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History of traffic lights

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History of traffic lights

Traffic lights are signalling devices positioned at road intersections, pedestrian crossings, and other locations to control flows of traffic. The history of traffic lights is associated with the historic growth of the automobile.

Traffic lights were first introduced in December 1868 in London to reduce the need for police officers to control traffic. Since then, electricity and computerised control has advanced traffic light technology and increased intersection capacity.

Before traffic lights, traffic police controlled the flow of traffic. A well-documented example is that on London Bridge in 1722. Three men were given the task of directing traffic coming in and out of either London or Southwark. Each officer directed traffic coming out of Southwark into London, making sure all traffic stayed on the west side of the bridge. A second officer directed traffic on the east side of the bridge to control the flow of people leaving London and going into Southwark.

On 9 December 1868, 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 proposed by the railway engineer J. P. Knight of Nottingham who had adapted this idea from his design of railway signaling systems and constructed by the railway signal engineers of Saxby & Farmer. The main reason for the traffic light was that there was an overflow of horse-drawn traffic over Westminster Bridge which forced thousands of pedestrians to walk next to the Houses of Parliament.

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. The signal was 22 feet (6.7 m) high. The light was called the semaphore and had arms that would extend horizontally that commanded drivers to "Stop" and then the arms would lower to a 45 degrees angle to tell drivers to proceed with "Caution".

At night a red light would command "Stop" and a green light would mean use "Caution". 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 pavement and injured the policeman who was operating it.

Despite the failure of the world's first traffic light in London in 1869, countries all around the world still made traffic lights. By 1880, traffic lights spread all over the world. The early traffic lights in the late 19th century were very different from the ones that exist now. 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.

One example was from Toledo, Ohio, in 1908. The words "Stop" and "Go" were in white on a green background and the lights had red and green lenses illuminated by kerosene lamps for night travellers and the arms were 8 feet (2.4 m) above ground. 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. The design was also used in Philadelphia and Detroit. The example in Ohio was the first time America tried to use a more visible form of traffic control that involved the use of semaphores. The device that was used in Ohio was designed based on the use of railroad signals.

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