Before the 1920s, the world of traffic signage was a veritable Wild West. The invention of the first electric traffic light in 1912 was a turning point that improved the speed and efficiency of traffic flow. But that faster flow of traffic highlighted the need for something else: road signs.
Like traffic lights, road signs evolved over time to become what we know today. Each road sign has its own story, and one of the most interesting stories is that of the stop sign. Here’s a look at why stop signs are red today — and why they were yellow first!
The Birth of the Stop Sign
Getting stuck at an intersection like the one above is never an enjoyable experience. But could you imagine how much worse it would be if there were no road signs?
The first electric traffic light was invented in 1912 and installed in 1914. It didn’t take long for people to realize that roads needed more than just lights. The first stop sign was installed soon after — it was put up in 1915 in Detroit, MI.
However, that stop sign bore little resemblance to the iconic red octagon we see in many countries today. It was a white square that measured two feet long on each side, and it had black lettering.
This design was straightforward enough. And since there weren’t nearly as many road signs in 1915 as there are now, drivers could spot this type of sign fairly easily.
Here’s the problem: cities and towns all over the world were installing stop signs. But because there was no type of standardization whatsoever, stop signs could look like just about anything. That made them difficult to pick out, and drivers can’t follow road signs if they can’t even see them!
Why Red Was the Initial Choice
When it comes to standardizing road signs, color is one of the most important elements. So when the National Conference on Street and Highway Safety (NCSHS) convened in 1924, selecting a color for the stop sign was of prime importance.
The NCSHS’s initial choice was red. After all, electric traffic lights had been in use for several years at that point, so drivers already had a connection between the color red and stopping.
Similarly, the science behind red traffic lights also applied to stop signs: of all colors, red is the one we can see from the furthest away. Or perhaps more accurately, the longer red wavelengths of visible light are able to travel further than shorter blue wavelengths:
You can see this phenomenon in action when you look at the sky at sunset or when there’s more air pollution than normal. As you might know already, the sky normally looks blue as a result of a phenomenon called Rayleigh scattering. In Rayleigh scattering, water droplets and other particles in the atmosphere absorb certain wavelengths of light and then radiate (“scatter”) those wavelengths in different directions.
Shorter wavelengths (like those of blue light) scatter more easily. That means that as sunlight shines into the atmosphere, blue light scatters early, making the sky look blue.
As the sun’s light travels further through the atmosphere, the next-longest wavelengths progressively scatter. Light with longer wavelengths (light closer to the red end of the spectrum) is harder to scatter, so that happens last.
When the sun is setting, the fact that it’s low on the horizon means that its light needs to travel through more of the atmosphere than it does during daylight. The more atmospheric particles sunlight runs into, the more it scatters. So as the sun sets, you see more red, orange, and yellow — the shorter wavelengths have been scattered off.
You see a similar effect during dust storms or other times when there’s a huge amount of air pollution. The extra particles from the pollution scatter more light, so sometimes, it’s primarily red or orange light that reaches our eyes.
Additionally, red really stands out against the natural landscape. There’s a lot of green in nature, and red is green’s complementary color!
Why Were Stop Signs Standardized to Yellow?
Unfortunately, there were a few logistical issues when it came to making stop signs red. One was that the color red was very difficult to see at night. When the light was low enough, a red sign just looked black. (At this point in time, there was no such thing as reflective paint or reflective coatings.)
Another factor was that at the time, every available form of red paint faded very quickly. If red became the standard color, stop signs wouldn’t just be hard to see in the dark — they also would require frequent repainting.
The NCSHS ultimately chose to set the standard stop sign color as yellow with a black border and black lettering. That standard stayed in place until 1954.
When (and Why) Did They Become Red?
By the time 1954 rolled around, there were far more options for finishes on road signs than there were 30 years prior. And it was thanks to two new innovations that traffic officials could finally have a stop sign in their initial color of choice: red. There was now fade-resistant coating to preserve that bright, noticeable red finish.
But perhaps even more critically, it was now possible to make the white border and white lettering reflective. More specifically, the material had a retroreflective finish. That means that when it’s illuminated (usually by headlights), it reflects light back in the same direction it came from. Retroreflective finishes are what make road signs appear to “glow,” as they do in the picture above.
In 1954, the Manual on Uniform Traffic Control Devices (MUTCD), a United States standard for traffic lights, road signs, etc., was amended to state that all stop signs were to be octagon-shaped and red, and stop signs have been red ever since.
Are Stop Signs Red Everywhere?
Many countries have stop signs that look identical (or almost identical) to the red octagon mentioned earlier. Part of that might be because the Vienna Convention on Road Signs and Signals includes this design as one of the two acceptable stop sign designs — the other is shown in the picture above.
The Vienna Convention on Road Signs and Signals isn’t a law governing international road signs. Rather, it’s a treaty that countries can opt to ratify — meaning they choose to adopt the Convention’s traffic signs and signals.
The purpose of this agreement is to establish at least some consistency in driving laws across nations. This is especially helpful in Europe, as the continent has many geographically small countries right next to one another.
Notably, even countries that haven’t ratified the treaty — like the United States and Japan — tend to have signs and signals very similar to the ones laid out in it.
While some countries used to have stop signs that were blue and/or yellow, every country now has a stop sign that has a significant amount of red. But while colors stay consistent, there’s some variation in design. Many countries have the familiar octagon with “Stop” in either English or the country’s local language.
A few countries, including Israel, have red octagonal signs featuring a hand instead of the word “Stop”:
Countries that follow the Vienna Convention can sometimes use light yellow instead of white on their stop signs. But when it comes to color, the common denominator is red.
This makes sense. When it comes to color symbolism, colors can have different meanings in different cultures. But when you look at traffic lights all over the world, it becomes clear that the attention-grabbing red has become a universal color for “stop.”
Bonus: Why Are Stop Signs Octagonal?
Now you know how the humble stop sign came to be bright red. Its shape was decided before its color was, but relatively few people are familiar with it.
The story starts in 1922 with three traffic professionals: A.H. Hinkle (Indiana Superintendent of Maintenance), Walter F. Rosenwald (a Minnesota maintenance engineer), and John T. Donaghey (a Wisconsin highway engineer). Tired of the lack of consistency across America’s road signs, the three set out on a road trip throughout their home states. The goal? To develop a plan for universal sign designs.
The plan ended up being accepted by the Mississippi Valley Association of State Highway Departments in 1923. The crux of that plan was assigning road signs different shapes based on danger. With that system, drivers would likely be able to understand the sign’s shape and act accordingly, even if they couldn’t read it at night. Remember, reflective paint hadn’t been invented yet.
At the time, railroad crossings were probably the most dangerous part of the road. The designers chose to use circular signage for these and other dangerous situations. For ordinary signs displaying regulations, they used rectangles.
The designers decided that stop signs fell somewhere in between. They weren’t strictly regulatory, but they also did more than just warn drivers of danger. In designing the stop sign, the team chose an octagon — a shape that they believed fell roughly between a circle and a rectangle.
The octagonal shape had another advantage, and if you drive regularly, you might have benefited from it without realizing it. Thanks to its distinctive shape, a stop sign can be easily recognized by cars coming from the opposite direction.
This can be very useful at intersections — some stop signs include a smaller sign below clarifying that the driver is at a four-way stop, but many don’t. If you can see which other drivers have stop signs and which don’t, getting through the intersection will be a lot less stressful!
The Stop Sign: An Ordinary Piece of History
Drivers and non-drivers alike are familiar with stop signs. And even though these distinctive signs are seemingly everywhere, many of us haven’t stopped to wonder why they’re the bright color and memorable shape that they are. Now that you know a little bit about the stop sign, you know more than just an interesting tidbit — you’ve learned a piece of national and international history.