DETROIT – The first tri-color, four-way traffic signal was installed at Woodward Avenue and Fort Street in Detroit in 1920.
William Potts, a traffic officer, invented the signal, adding the yellow light. Signals with red and green lights had been in use since the first traffic light was invented in London in 1868.
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The idea to add the yellow light came from railroads, which were already using three lights. It would become a standard for vehicle traffic by the next decade.
That first three-color, four-way traffic signal is on display at The Henry Ford Museum in Dearborn.