In which country was the first electric traffic signal installed?

The first electric traffic signal was installed in the United States, at Cleveland, Ohio, in August 1914.

The American Traffic Signal Company placed the device at East 105th Street and Euclid Avenue. It used electrically illuminated red and green signals and a buzzer to warn drivers when the indication changed. The system was manually operated, but it replaced the need for an officer to direct every movement by hand.

An earlier electric design had been developed in 1912 by Lester Wire, a police officer in Salt Lake City, Utah. That makes Utah important to the invention story, but Cleveland is generally credited with the first installation. The United Kingdom had an earlier gas-lit signal in London, installed in 1868, but it was not an electric traffic light.

Cleveland’s signal was also not the modern three-color arrangement. Detroit engineer William Potts created the first four-way, three-color traffic signal in 1920, adding yellow between stop and go.