This Is Why Traffic Lights Are Red, Yellow, and Green

Ever wondered why blue doesn't mean go and brown mean stop? Turns out, there's a perfectly good explanation for it.

The idea that red means stop and green means go has impacted our lives in more ways than just traffic signals. We have been taught from a young age that the color red means danger and the color green means it’s OK to move forward. But why were those particular colors chosen for traffic lights in the first place? For something we have to look at every day, why couldn’t they have been prettier colors like magenta and turquoise? While you’re in the mood to learn, here are explanations for other little things you’ve always wondered about.

The first stoplights

The first traffic lights in the United States were installed because of an increase in travelers on the road. Worried about accidents, towns and cities would install traffic towers to help the flow of cars. Officers manned the towers and used whistles and red, green, and yellow lights to indicate to drivers when they should stop and go.

Then, in 1920, William Potts created the first tri-color, four-direction traffic signal. It helped drivers stay safe at intersections. The very first four-direction traffic light was installed at Woodward Avenue and Fort Street in Detroit, Michigan. Throughout the country, there were still a lot of systems for traffic lights and patterns in place. Since this could end up causing more problems for drivers, the Federal Highway Administration created “The Manual on Uniform Traffic Control Devices” in 1935 that set uniform standards for all road signs, pavement markings, and traffic signals requiring them to all use red, yellow, and green light indicators.

The history of the colors

Well, it’s important to know that before there were traffic lights for cars, there were traffic signals for trains. At first, railroad companies used red to mean stop, white to mean go, and green to mean caution. As you could imagine, train conductors ran into a few problems with the color white meaning go—bright white could easily be mistaken for stars at night, with train conductors thinking they were all clear when they really weren’t. Railway companies eventually moved to the color green to mean go, and the color yellow to mean proceed with caution since it’s easily distinguishable from the other colors, and it’s been that way ever since and when traffic lights were put up it became standard for them as well—except in Japan, where you’ll find an entirely different color that signals “go.”

As far as red goes, that’s always been a color that indicated danger, long before cars were even around. Red is the color with the longest wavelength, so it can be seen from a greater distance than other colors. The color yellow was used to caution drivers because it has a slightly shorter wavelength than red, but not as short as green.

But, believe it or not, yellow was once used to mean stop, at least as far as signage goes. Back in the 1900s, some stop signs were yellow because it was too hard to see a red sign in a poorly lit area. Eventually, materials were developed that were highly reflective and red stop signs were born. Since yellow can be seen well at all times of the day, school zones, some traffic signs, and school buses continue to be painted yellow. Keep these safe driving tips in the back of your mind whenever you see a yellow light.

So next time you’re impatiently waiting at a traffic light, don’t get so mad; employ these driving etiquette rules first and know that traffic lights have certainly come a long way.

Popular Videos

Morgan Cutolo
Morgan is the Assistant Digital Managing Editor at Reader’s Digest. She graduated from the University of New Hampshire in 2016 where she received her Bachelor of Arts in Journalism. When she’s not writing for rd.com or keeping the 650+ pieces of content our team produces every month organized, she likes watching HGTV, going on Target runs, and searching through Instagram to find new corgi accounts to follow.