Automotive Wiki: Why Are Traffic Lights Red, Yellow and Green?

A traffic light is a common thing nowadays and you, just like all the other drivers, must obey the rules: if it's green, you pass, if it's red, you stop, and if it's yellow, you act with caution.

There's no doubt that traffic lights are a must in the crowded cities we're living in and no matter how hard we try, they represent the only way to control traffic when a police man is not around.

Of course, we, as everyday drivers, can't imagine a typical home-to-office trip without at least a traffic light, but there was a time when all roads were traffic lights-free. Sure, at about the same time, roads were more or less car-free as well, but let's just pretend we didn't say that...

Getting back to the first phrase of this article, there are some obvious rules to obey every time you jump behind the steering wheel of your car. Traffic lights are the same all over the world and comprise three different colors, all having the same purpose in every single country on planet Earth: green – go, red – stop, yellow (or amber) – be cautious.

But how come all traffic lights are red, yellow and green? Why aren't they purple, fuchsia and jonquil? Well, there are multiple speculations on these topic, but before jumping straight into the main subject, let's take a few minutes for a short history lesson.

It's a well-known fact that the automotive industry has been the pioneer of many important things used nowadays all around the globe, but in its turn, the automotive world also borrowed some vital elements from the rest of the industries as well. Among them, traffic lights.

The first traffic light in the world, if it could be really named so, saw daylight in 1868 in London and was exclusively used to control railroad traffic at the intersection of George and Bridge Streets. The design was pretty basic, but it still helped the “innovative” technology serve its purpose pretty well: it was made of two vertical arms that could move in a horizontal position to inform incoming trains that they need to stop. At a 45-degree angle, the system had the same role as the yellow color these days: caution for all incoming traffic.

And now the fun part: because at night the signaling device was obviously invisible, railroad engineers mounted simple lights to signal the stop and caution positions. Their color choice? Red for stop and... green for caution.

You're probably wondering how come green was the color they picked for caution... Well, nobody knows for sure, but things changed a few years later, especially once the traffic lights made way in the automotive industry.

This extremely important moment took place in 1912 in the United States (where else?) thanks to Lester Farnsworth Wire, in charge of the traffic division of the Salt Lake City Police Department. Operated manually, the first automotive traffic light had just two colors, red and green, and was installed in Salt Lake City at the intersection of Main Street and Second South. Although only a few cars were on the road at that time and traffic regulations were almost non-existent, drivers were simply amazed by the new invention, so a policeman was absolutely necessary to force them obey the new rules.

Getting back to the choice of the three magic colors, it is believed that the first time traffic lights have been used in the railroad system they relied on a different trio, red for stop, green for caution and white or clear for go. While the two might have a more or less obvious meaning, the white light was the one giving headaches to authorities. The surrounding white lights, be they stars or simply lights on the street, made train engineers believe they can pass freely, which led to multiple fatal collisions.

California Department of Motor Vehicles campaign to teach drivers the meaning of traffic light colors

Red is mostly associated with blood and thus the color was selected for signaling “stop” to all incoming vehicles, be they cars or trains. Since it symbolizes a dangerous situation that could have serious consequences if ignored, red has always been the main choice for all traffic lights across the world in order to force approaching vehicles stop and thus avoid potential collisions.

As for green, it's the same color symbolism that stands as the reason for using it in traffic lights. Just like red, it is the source of different human emotions, in this case showing a relaxing thing, such as nature or any other healthy element that wouldn't have such a powerful impact on drivers seeing it. Plus, green can be easily noticed during the night and, there are basically no other surrounding lights that could mislead drivers into believing they have a go.

Yellow is the color pick that raised most eyebrows every since it was used in the traffic light system. It signals caution and it replaced green, which was the first color pick for railroad traffic light systems. Still, most people think that yellow symbolizes the sun, which is again one of the things that could relax drivers and less an element to trigger caution. Nevertheless, it's a good choice for the night because a yellow light can be easily seen from distance but, as compared to red and green, the surrounded lights can easily confuse incoming drivers.

Traffic lights evolved a lot over the year, especially to address color blindness and thus become much more effective. It's a well known fact that authorities all over the world designed new traffic lights to address this issue, be they double-red lights or differently-shaped lights, but the classic design has been lightly altered to increase its efficiency.

Since red-green blindness is one of the most common forms of visual impairment, these days' red light comes with a limited amount of orange, which allows color blinded people to notice the stop signal. Additionally, the green light contains blue for the same purpose. Obviously, more revolutionary designs have already been presented, and you can read more about such a technology here.
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About the author: Bogdan Popa
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Bogdan keeps an eye on how technology is taking over the car world. His long-term goals are buying an 18-wheeler because he needs more space for his kid’s toys, and convincing Google and Apple that Android Auto and CarPlay deserve at least as much attention as their phones.
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