Tech of the past: Traffic Light
The modern traffic light, with red, yellow, and green lights, was first used in Detroit. Originally, traffic lights only had red and green, but Detroit traffic officer William Potts added the amber light to warn drivers that the light was about to change red. This design, created in 1920, was standard across the country by the mid-1930s.
Photo by Wally Bahny for TechRepublic