William Potts (May 1883 – 1947) was an American police officer who is known for creating the modern, three-lens traffic light in Detroit in 1920. A two-lens, gas-powered red/green traffic signal was invented in London in 1868 by John Peake Knight. However, after a short test, traffic lights were not used in the United Kingdom again until 1929.

Biography

Potts was born in Bad Axe, Michigan. The 1900 census records Potts as 17 years old and working as a police officer. By 1910, he was married to Grace (Baker) Potts, and they had four children. Potts later became the "superintendent, signal person police" for the city of Detroit.

The old way of directing traffic with police officers had become less effective. Two-color traffic signals, using green and red lights, existed at the time, but they did not give drivers enough time to stop when driving fast. Some cities tried keeping the green light on for a few seconds after the red light turned on, to warn drivers that the right of way was about to change. In 1917, Potts created a new system by adding a "yellow" or "amber" light. This light would appear after the green light and before the red light, signaling that a change was coming.

In 1920, Potts designed the first four-way traffic signal with three colors. It was installed at the intersection of Woodward and Michigan Avenues in Detroit in October 1920.

In popular culture

In the SyFy series The Magicians, Potts got the idea to create the three-color traffic light after seeing the colors that the moon had.