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 colour red means danger and green means it’s OK to move forward. But why were those particular colours chosen for traffic lights in the first place? For something we have to look at every day, why couldn’t they have been prettier colours like magenta and turquoise?
Well, it’s important to know that before traffic lights for cars even became a thing, 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 white meaning go. For instance, one train conductor mistook a bright star for a white light and thought he was all clear. Because of incidents like that, railway companies eventually moved to green meaning go, and it’s been that way ever since.
As far as red goes, that’s always been a colour that indicated danger, long before cars were even around. This most likely started because it’s the colour with the longest wavelength so it can be seen from a greater distance than other colours. As far as yellow goes, it 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.
So next time you’re impatiently waiting at a traffic light, don’t get so mad at them; they’ve certainly come a long way.