<P> William Potts (May 1883--1947), a Detroit police officer, is credited with inventing the modern, three - lens traffic light in Detroit in 1920 (the two - lens, red / green traffic signal was invented in London in 1868). </P> <P> William Potts was born in Bad Axe, Michigan . The 1900 census lists Potts as 17 years old and a police officer . By 1910, he was married to Grace (Baker) Potts, and they subsequently had 4 children . By 1920, Potts had become the' superintendent, signal person police' for the city of Detroit . Charged with finding a way to control traffic and with the old system of police directing traffic increasing outmoded (there were some two - color signals, with green and red lights already), Potts invented a' yellow' or' amber' light which removed the need for police to switch the signal . </P> <P> The first four - way traffic signal tower in the world was located at the Woodward and Michigan Avenue intersection in October 1920 . The tower was manually operated and had 12 lamps, three in each direction . In December 1920, signals were added along Woodward Avenue at Grand River, State, Fort and Congress, but all were controlled from the manual tower at Woodward and Michigan . </P> <P> Then in 1921, Potts, who was a Superintendent of Signals for the Police Department, installed his first automatic signal light system in 15 towers . During the next 25 years the location and operation of traffic lights throughout the world changed considerably, but the original principle developed by Potts remained . The last traffic tower in Detroit was removed from East Jefferson and Grand Boulevard in 1930 . The traffic light system has been modernized with corner posts, hanging center lights and mast arm extensions . </P>

Who invented the 4 way automatic traffic light
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