Why are traffic lights red, yellow and green?


Have you ever sat at a traffic light and wondered why the lights are the color they are? It’s not something we ever really consider, but when you’re waiting a good few years for the light to turn green again, the thought might cross your mind. Why red, yellow and green? Blue’s a perfectly good color, as is pink, or purple. Why aren’t they ever used? It turns out there’s an excellent reason for it.

Train signals

Cars haven’t always been around. While they might not be anything new in our lifetime, it wasn’t until the late 1800s that the concept of the automobile came to fruition. Since then, our roads have been filling up with more and more cars, leading to all the traffic delays we so hate dealing with. While cars might only be a century or so old, traffic lights aren’t. In fact, they’re older.

Before we had automobiles, there were trains. Although they function differently to cars, there’s still a system in place to keep them from crashing into one another. This is where the traffic lights originated from. Back in the 1830s, there were three colors used to represent different things. Red meant to stop, green meant caution and white meant to go. It’s not quite the pattern that we’re used to nowadays, and it wasn’t without its problems. It turned out that white wasn’t a useful color to use, because there were multiple incidents of people mistaking a light elsewhere for a sign they could go. When the red lens fell out of a signal in 1914, it led to a horrendous crash because the driver saw the red light as a white one.

So, out with the white and in with the green. Yellow was brought in as a replacement for the caution color, and the traffic lights we’re familiar with were put in place.

Why those colors?

There are various reasons why these colors were used for their respective signals. Red has always been used to signify for a vehicle to stop, and that’s because the color is most commonly associated with danger. It’s been that way for centuries, so why stop now? Red is a very intense color, and is also scattered less by air molecules. This means that a red light can reach a great distance, even if affected by weather conditions like rain or fog.

As for green, not much is known about why it was used in the first place. However, the color is a stark contrast to red, which may explain why it was initially chosen. The same was the case with yellow when it was picked as the new color for caution. It was shown to stand out differently from the other two and wouldn’t be confused by train drivers on the railway.

Funnily enough, yellow is another color that was once used to signify danger. Unlike red, it’s clearer to see in darker conditions. This made it a useful color for signs which would be needed at night. These decreased in popularity when more reflective materials were designed, and red became commonplace as a sign to stop on the roads.

The arrival of the traffic light

It wasn’t until 1935, some 100 years after the signals were first established on railway lines, that the traffic system we know today was put in place. When cars started to appear, people up and down the country attempted different ways to control the flow of traffic. Some used police officers, others honking systems, but none of them were hugely effective. Several of them started to incorporate the color signals from the railway, which is how they eventually became commonplace on the roads.

You learn something new every day. If you always wondered how traffic lights came to be, now you know that they got their origins on the railroads. Unfortunately, this newfound knowledge won’t help you in any way the next time you get stuck in traffic.