Book 3, Question 90
Why Do Traffic Lights Change?
A traffic light is a turn-taking machine. It gives each direction a safe slice of time, so cars and walkers do not all move at once. A controller box runs a timer, and sensors in the road or cameras can skip a turn if no car is waiting.
From the book
Page from A Million Whys Book 3
More fun facts
- The first traffic lights were invented to handle chaotic traffic from horse-drawn carriages.
- Today there are about two million traffic lights in the United States.
- In 1919, a teacher in Cleveland invented a game to teach children traffic signals. Kids still play a version of it called Red Light, Green Light.
- Traffic engineers can give more green time to busy roads than to quieter ones.
- Smarter traffic light timing tested by researchers cut rush-hour travel times by 22 percent.
Sources: Smithsonian Magazine, Smithsonian Magazine, Smithsonian Magazine
Questions kids ask
Where did Red Light, Green Light come from?
A Cleveland teacher invented a game in 1919 to teach children traffic signals, and kids still play a version of it.