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.
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.