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 to control the flow of traffic. Traffic lights usually consist of three signals, conveying meaningful information to road users through colors and symbols, including arrows and bicycle symbols. The usual traffic light colors are red to stop traffic, amber to signal a change, and green to allow traffic to proceed. These are arranged vertically or horizontally in that order. Although this is internationally standardized, 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 computerized 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.