Traffic light
signalling device to control competing flows of traffic
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.
History
In December 1868, the first traffic signals showing a red or green light at night were installed outside the Houses of Parliament in London. They were invented by John Peake Knight.
The public source identifies “Traffic light” as signalling device to control competing flows of traffic. This brief keeps that definition visible, then builds a research path around Traffic, light and signalling.
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The citation trail is more important than the brevity of the summary: it shows where individual claims can be examined in context. The source revision retrieved here is dated Sep 1, 2026. The linked authority identifier is Q8004. The Library of Congress control number is sh85042377. 1 of 2 selected statements include explicit references; 1 carry qualifiers and 0 use preferred rank. The first chronological checks are 1868.
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This entry incorporates text from “Traffic light” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.