The world's first electric traffic signal is put into place on the corner of Euclid Avenue and East 105th Street in Cleveland, Ohio, on August 5, 1914.

What did they use before traffic lights?

Up until the 1900s in the United States, police officers primarily manually directed traffic through a combination of using hand signals from towers which allowed them to get a good view of traffic. However, in some areas red and green gas powered lights were used.

When did traffic lights become common in the UK?

The first traffic signals in Britain (and indeed the world) were installed outside the Houses of Parliament on 10 December 1868. They used contemporary railway signalling technology – semaphore arms for day-time use and green or red gas lamps at night.