Green highway signs are everywhere, but why are they green?
When you’re driving down the highway, you naturally pay attention to traffic signs. But do you ever think about why they look the way they do or why they’re a certain color? Take the green ones. Green highway signs, also called guide signs, are everywhere, and we pass them by without much thought. But their design has a big role in getting us where we need to go safely.
Why are highway signs green? Believe it or not, a lot of brainpower has gone into that decision. And there are logical reasons behind using green over, say, purple or hot pink. To get some historical perspective, including why we have green traffic signs and where you’ll find them, we spoke to Kevin Marshia, director of engineering at the American Association of State Highway and Transportation Officials in Washington, D.C.
Keep reading to learn all about this important feature of American highways.
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Why are highway signs green?
You know green means “go” on traffic lights, but what’s behind the decision to make highway signs that color? Here’s why, when it comes to highway signs, it’s easier being green:
They’re highly visible
You want a highway sign to be easy to see and read. “Hundreds of drivers participated in a survey in the late 1950s where several different colors of signs were used along a section of a highway,” Marshia says. “The results of that survey were that 58% of drivers indicated that a green sign with white lettering was most visible.”
One reason green is more visible? It’s the easiest color for the eye to process. That’s because the photoreceptors in our eyes, called rods and cones, detect light at different wavelengths. The color green falls in the middle wavelength (between blue and red), and this is the wavelength where our perception is at its best.
Size and design also play a role. “A green sign with white letters is highly visible to the traveling public because they tend to be bigger than other highway signs and designed so you can see it at a distance, even at night,” Marshia says. The Federal Highway Administration (FHWA) points out that many green highway signs have external lights or a special reflective coating. “The retroreflective sheeting reflects lights back to the driver, making it easier to see the sign’s lettering at night and during times of limited visibility, such as rain or fog,” explains Marshia.
They fade less
One reason why highway signs are green may be their ability to retain their color over time. “The color of a sign and/or the exposure to the sun can have an impact on how quickly the color fades,” Marshia says.
Research has shown that after years of being exposed to daylight, certain colored traffic signs fade faster than others. In fact, one study in the International Association of Traffic and Safety Sciences found that green signs had an estimated lifespan of 42 years, compared with 35 years for a yellow sign and 12 for a red sign. Blue and white signs were shown to last the longest, at 45 and 75 years, respectively.
“Historically, green signs do not tend to fade as quickly as red signs; however, new technologies in sign sheeting material have decreased the rate of fading,” he says.
They’re not distracting
According to the Arizona Department of Transportation (ADOT), green is considered a “cool color” and blends in enough to be part of the natural scenery, like trees and grass. In other words, it won’t take the driver by surprise upon seeing it. ADOT says green highway signs aren’t as distracting as yellow, orange or red, which stand out more.
Those brighter colors are used to catch a driver’s attention and to warn of what’s ahead on the road. “There are various standard colors of signs in the U.S., and this standardization helps set drivers’ expectations on all public highways,” says Marshia. “For instance, yellow indicates warning, such as an upcoming pedestrian crossing or curve in the roadway. Orange signals construction, and red is typically reserved for stop or yield conditions.”
Green traffic signs also tend to be easier on the eye than other colors. Research has shown that the color green has a calming and anxiety-reducing effect, and it can even significantly reduce your heart rate. And when you’re driving on the highway, you definitely want to be as relaxed as possible—not stressed out by highway signage.
What’s the history of green traffic signs?
Traffic and road signs have existed in the U.S. since the early 1900s. But back then, there was no uniform color or shape—states, cities, towns and automobile associations all designed and put up various traffic signs with different colors. The problem was, depending where you were driving, you had no idea which sign meant what. The FHWA found that on 40% to 50% of the more-traveled roads, it was common to encounter as many as 11 different signs for one single trail or route!
In 1927, with driving becoming more prevalent and roads expanding, it became apparent that there was a need to standardize traffic signs. This led the American Association of State Highway Officials to publish the first edition of the Manual on Uniform Traffic Control Devices (MUTCD). The 1935 document classified the shapes and colors of signs used to guide, regulate traffic or warn drivers, and it defined pavement markings.
But green signs weren’t specified right away. With the advent of the U.S. Interstate Highway System in the 1950s, the federal government realized that drivers needed a way to easily read directional signs from a distance, and the country needed a uniform, nationwide system. The fourth edition of the MUTCD, published in 1961, mandated green signs with white lettering for the highway guide signs—the same design we use today.
Are all highway signs green?
Guide signs are green, but highway signs also come in many other colors. As previously mentioned, you can find yellow, orange and red signs on highways and major roads, along with white signs with black lettering or symbols. You’ll also see other colored signs on highways, including blue and brown, which have their own meanings.
“While interstate route numbering signs are blue, generally blue signs with white lettering are service signs, letting the driver know about forthcoming rest stops, gas stations and lodging,” says Marshia. “Brown signs on highways are there to point out recreational or other places of interest, such as parks, campgrounds and historical sites.”
What color are highway signs in other countries?
Many places try to make it easier for all drivers—visitors and residents alike—to avoid deciphering a slew of different regional signs. That’s why guide signs are often blue or green in other countries. But as you would expect, the colors, language and symbols appearing on these signs can differ depending on the region.
If you’re traveling abroad, you can expect to see red stop signs and yellow, diamond-shaped warning signs to urge drivers to reduce speed because of a hazard ahead. White-on-blue signs indicate future exits for restaurants, restrooms and gasoline. Thanks to the Vienna Convention on Road Signs and Signals of 1968, created by the United Nations, there’s a standardized system of signs within the countries that have signed the agreement. Signatories include countries in the European Union, Middle East, Africa and Latin America.
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Sources:
- Kevin Marshia, director of engineering at the American Association of State Highway and Transportation Officials; phone and email interviews, October 2025
- Federal Highway Administration: “Sign Materials”
- CNN: “Why we all need green in our lives”
- Arizona Department of Transportation: “Ask ADOT: Why are Highway Signs Green?”
- IATSS Research: “Assessing the color status and daylight chromaticity of road signs through machine learning approaches”
- Federal Highway Administration: “Manual on Uniform Traffic Control Devices (MUTCD); The Evolution of MUTCD”
- National Archives and Records Administration: “National Interstate and Defense Highways Act (1956)”
- United Nations Treaty Collection: “Convention on Road Signs and Signals”
