Traffic lights (or traffic signals) are lights used to control the movement of traffic. They are placed on roads at intersections and crossings. The different colors of lights tell drivers what to do.
Traffic lights change their colors in the same order every time. In most English-speaking countries, traffic lights usually change in this order:
- Red light on: This tells drivers to stop.
- Green light on: This means the driver can start driving or keep driving.
- Yellow light on: This tells drivers to stop when it is safe to, because the light is about to turn red.
William Potts, a police officer, invented the first traffic light with three colors.