Explained: this is why traffic lights are green, red and yellow

traffic lights

Have you always wondered why traffic lights have these colors?

One day, someone had to pick colors for the traffic lights and they decided on green, yellow and red. Why is that? Maybe you have never really thought about this. Or maybe you have wondered this for years. Either way, you will get an answer to this question today! Find out more below.


To find out why these colors were chosen, it would be helpful to know where traffic lights (and their colors) come from. In 1910, the first traffic signals were installed in the country. Officers were using whistles and lights to maintain the flow of cars by letting drivers know when to stop or go. In 1920, William Potts created the first traffic light. At that time, there were no rules about the kind of lights or patterns that had to be used. And so, these lights would look different everywhere you went. In 1935, the Federal Highway Administration set up the “Manual on Uniform Traffic Control Devices” that held standards for all signs and signals. That manual also required the traffic lights to be red, yellow and green everywhere.


So, where did the specific colors come from? Before the traffic lights, trains already used light signals to help with the flow of train traffic. In these traffic lights red meant stop, white meant go and green meant ‘proceed with caution’. When the color white caused issues (it could be mistaken for something else by train drivers, causing accidents), they moved from white to green for the sign for ‘go’. And because yellow was more distinguishable, they made yellow the color for ‘proceed with caution’.


But then why red? The color red is the color with the longest wavelength. And that means that you can see it from further away. And that is very helpful when it comes to warning signs and traffic lights that want you to stop for safety.

Now you know why the traffic lights have the colors they’ve had for a hundred years. Definitely a fun fact to share at parties!

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Source: The Family Handyman | Image: Unsplash, Jonny Rogers