The world’s first traffic light was installed in London in 1868.
The signal stood outside the Houses of Parliament at the intersection of Bridge Street and Parliament Street. It was designed by railway engineer J. P. Knight and operated with gas lamps displaying red and green signals. A police officer manually controlled the mechanism.
This early installation predated the electric traffic lights used today. In January 1869, the gas-powered apparatus exploded, injuring the officer operating it, and the experiment was abandoned. Traffic signals did not become common again until technological improvements made electric systems practical.
Modern traffic lights use red, yellow or amber, and green lamps, but their exact sequences and flashing rules vary by country. The London installation is nevertheless widely recognized as the first traffic signal intended to control road traffic.