Traffic light

Signaling device to control competing flows of traffic / From Wikipedia, the free encyclopedia

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Traffic lights, traffic signals, or stoplights – also known as robots in South Africa[1][2] – are signalling devices positioned at road intersections, pedestrian crossings, and other locations in order to control the flow of traffic.[3]

An LED 50 watt traffic light in Portsmouth, UK
A traffic light in Jakarta, Indonesia with its count-down timer. A pedestrian crossing is also shown.

Traffic lights consist normally of three signals, transmitting meaningful information to drivers and riders through colours and symbols including arrows and bicycles. The regular traffic light colours are red, yellow (also known as amber), and green arranged vertically or horizontally in that order. Although this is internationally standardised,[4] variations exist on national and local scales as to traffic light sequences and laws.[5]

The method was first introduced in December 1868 on Parliament Square in London to reduce the need for police officers to control traffic.[6] Since then, electricity and computerised control has advanced traffic light technology and increased intersection capacity.[7] The system is also used for other purposes, for example, to control pedestrian movements, variable lane control (such as tidal flow systems or smart motorways), and railway level crossings.