William Potts (May 1883 – 1947) was a Detroit police officer who is credited with inventing the modern, three-lens traffic light in Detroit in 1920. (A gas-powered, two-lens, red/green traffic signal was invented in London in 1868 by John Peake Knight, though after a short test installation, traffic lights were not seen again in the U.K. until 1929.)[1]