Traffic lights were first invented in 1868, when a gas-powered signal was installed outside the Houses of Parliament in London to control horse-drawn traffic and pedestrians. The first modern-style electric traffic signals appeared later in the early 1900s, with a notable electric system installed in Cleveland, Ohio, in 1914.

Early invention (1868)

  • The earliest known traffic light went into service on December 9–10, 1868, at Bridge Street and Great George Street in Westminster, London.
  • Designed by railway engineer John Peake Knight, it used semaphore-style arms by day and gas lamps (red and green) at night, operated manually by a police officer.

Why it didn’t last

  • The gas-lit installation suffered a serious explosion a few weeks later, badly injuring the officer operating it.
  • Because of the safety risk, the experiment was abandoned and traffic control reverted to human officers for several decades.

Rise of electric traffic lights

  • In 1912, Lester Wire in Salt Lake City created an early electric red–green signal mounted on a pole, manually controlled but much safer than gas.
  • A widely credited “first electric traffic signal” following a patented system by James Hoge was installed on August 5, 1914, in Cleveland, using illuminated “STOP” and “MOVE” signs at an intersection.

Three-color system arrives

  • In 1920, Detroit police officer William Potts added the yellow/amber phase, creating the first three-color traffic light to better manage busy intersections.
  • This three-color red–yellow–green system spread through U.S. cities and later worldwide, forming the basis of the traffic lights used today.

Quick recap

  • First traffic light (gas, semaphore): London, 1868.
  • First practical electric systems: early 1910s, notably Cleveland, 1914.
  • First three-color light (red–yellow–green): Detroit, 1920.
    These milestones mark the evolution from experimental signals to the modern traffic lights that organize today’s road traffic worldwide.