Traffic light

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This diagram shows a traditional traffic signal in the U.S. Picture 1: A red light means stop.
Picture 2: A green light means go.
Picture 3: A yellow light means slow down or stop.
A traditional traffic signal in the United Kingdom. 1: Red means stop. 2: Light is about to switch to green. 3: Green means go. 4: Light is about to switch to red; stop if possible.

Traffic signals are instruments that use changing lights to control traffic. The different lights tell drivers what to do.

Light cycles[change | change source]

Traffic signals change their colored lights in the same order every time. In the United Kingdom and the United States, most traffic signals change in this order:

  1. Red light on: This tells drivers to stop.
  2. Red and amber/yellow lights both on: In the United Kingdom, this signals that the light is about to turn green. In some parts of the United States, it signals that pedestrians can cross the road. In other parts of the United States, traffic signals do not use the red and yellow lights together, and traffic lights go straight from red to green.
  3. Green light on: This means "go."
  4. Amber/yellow light on: This tells drivers to stop if they can safely, because the light is about to turn red.

History[change | change source]

Garrett A. Morgan, an African-American inventor, invented one of the first traffic lights. He was one of the first people to get a patent for a traffic light.

William Potts, a police officer, invented the first traffic light with three colors.