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Why Traffic Lights Are Red, Yellow, and Green

The red, yellow, and green lights of a traffic light are lit up.
ako photography/Shutterstock.com

Have you ever wondered why traffic lights are red, yellow, and green? Sure, we all know that red means stop and green means go. We learn that when we’re children still riding in car seats. But what’s the story behind traffic light colors?

Believe it or not, the first traffic lights weren’t for directing car traffic. They were designed for trains and they were red, green, and white.

Since red is a color often used to warn of danger, a red light meant “stop” even back then. Green was the sign meaning “caution,” while white meant “all clear.”

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Interestingly, red is the easiest color to see from a distance (thanks to its long wavelengths). This makes it perfectly suited to warn of danger. Green is also easy to see, but some legends suggest that white became confusing, especially in the dark when stars were bright and distracting.

Supposedly, this presented a need for a different color, especially as cars became more popular and traffic control was increasingly necessary.

The color yellow entered the chat for a lot of traffic signs. Yellow was commonly used for Yield and Stop signs since red was harder to see in low-light areas (remember, this was before headlights were as powerful or reflective, non-fading signs were invented).

As technology developed in both sign design and headlight strength, red became the sign for “stop,” yellow shifted into “caution,” and green took its place as “go!”

Now, the next time you’re stopped at a red light or trying to high-tail it under a yellow, you’ll know how those colors came to be.

Abbey Ryan Abbey Ryan
Abbey Ryan is a storyteller, preferably of stories in written form. Across the 5 years of her professional writing career, her work has been featured in The Chicago Tribune, Amazon, The Medical News Today, and more. When she's not writing (which is rare), she's likely traveling, painting, or on the hunt for a good snack. Read Full Bio »
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