Why are traffic lights red, yellow and green?
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Why are traffic lights red, yellow and green?

Oct 06, 2023

Confusing Traffic Lights At A Busy Intersection (Storyblocks)

by: James Wesser

Posted: Nov 11, 2022 / 10:40 AM EST

Updated: Nov 11, 2022 / 11:37 AM EST

(WHTM) — We see traffic lights all the time. Sometimes we get green lights, and sometimes we hit all the red lights on our commute to work.

But, while sitting at a red light, have you ever wondered why traffic lights are red, yellow, and green?

The first traffic light came into existence in the United States back in the early 1900s. These were called semaphore traffic lights. They would have retractable arms with the words "stop" and go" on them, similar to railroad crossing arms. They would also only have red and green lights. These types of traffic lights were popular in cities like Chicago where traffic was on the rise.

The yellow light would not come into play until the 1920s. William Potts, who was a police officer in Detroit, is credited for designing the first three and four-way colored traffic lights. The amber light was introduced during this time.

In 1923, African American inventor Garret Morgan designed an affordable and modern solution for the traffic light and patented a t-pole design that meant it was visible and safe. Morgan also patented it in Canada as well as the United Kingdom

There are a few reasons why the colors red, yellow, and green were chosen for traffic lights.

Red is an obvious choice. The color red means danger or to be alert for something occurring. It is the same reason why stop signs are red. The human eye is more apt to be attracted to something that is red, according to the National Library of Medicine.

Yellow lights were chosen to alert drivers that the light will change to red in a few seconds. An interesting fact about this light, according to idriveafely.com is that a yellow light should last longer if the speed limit is higher.

For example, if the speed limit is 45 miles per hour that yellow light will be on for a shorter time than if the speed limit was 55 miles per hour.

Green was picked because of how the color is pleasant to the eye. Green has a shorter wavelength which makes it easier to see. Before the color green was chosen, white was used. But, this color was easily confused, as street lamps used white lights. Since then the universal color for "go" has been green.

The Vienna Convention on Road Signs and Signals Treaty is the main reason why red, yellow, and green lights are used internationally. Ironically, the U.S and Japan have not signed the treaty, so deviations from these standards are found in those countries.

For the most part, traffic lights mean the same thing in every state throughout the U.S. And no, yellow lights do not mean to speed through so you don't hit a red light!

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