The first gas-lit traffic signals were installed outside London’s Houses of Parliament in 1868. They were introduced in Parliament Square to help control the growing flow of horse-drawn traffic and make it safer for pedestrians, including members of Parliament crossing nearby streets.
The system was designed by John Peake Knight, a railway engineer who adapted the idea of railway semaphore signals. During the day, movable arms indicated whether traffic should stop or proceed. At night, red and green gas lamps provided the visible instructions. A police constable operated the mechanism manually.
This early signal looked very different from a modern traffic light. It had no electricity, amber phase, or automatic timing, and it was intended mainly to support police control rather than replace it. The experiment was short-lived: on 2 January 1869, a gas leak caused the apparatus to explode, injuring the officer operating it, and the signal was removed.
Electric traffic lights appeared decades later. The first electric systems were developed in the United States during the early twentieth century, while the familiar three-colour arrangement became established later. London’s 1868 experiment nevertheless marked the beginning of traffic-signal history.