Traffic light

Traffic lights, traffic signals, or stoplights – also known as robots in <a href="/facts/South_Africa/vvXQpLgq">South Africa</a>, <a href="/facts/Zambia/lCnlx5a1">Zambia</a>, and <a href="/facts/Namibia/ahXuaypy">Namibia</a> – are signaling devices positioned at <a href="/facts/Intersection_(road)/b51M4MQx">road intersections</a>, <a href="/facts/Pedestrian_crossing/PHEJkAgH">pedestrian crossings</a>, 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, <a href="/facts/Amber_(color)/gGn5PFcK">amber</a> 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 <a href="/facts/Parliament_Square/SR7jAy0D">Parliament Square</a> in <a href="/facts/London/KozCCsy9">London</a> 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 <a href="/facts/Reversible_lane/uxDWDINk">tidal flow</a> systems or <a href="/facts/Smart_motorway/fxG54Cq2">smart motorways</a>), and railway <a href="/facts/Level_crossing/mUGbbLGF">level crossings</a>.

Traffic light open-in-new

Traffic light