Discover how the colors red, green, and yellow became the universal signals for stop, go, and caution as we trace the origins back to 19th-century railroads and the science of light. |
I t's common knowledge that green means "go," red means "stop," and blue means you'd better pull over and hope for a warning this time. But before motor vehicles existed and the rules of the road were established, the relationship between "green" and "go" didn't exist. This connection was established in the 1840s, when British railroads adopted a new color-coded warning system to alert train conductors. Over the next century, it evolved into the green, yellow, and red traffic-light system still used today.
If we look to nature, we can find answers as to why the color red was originally selected by railroad operators to convey a message of dire warning. According to a physicist, red shades are seen most clearly through fog and smoke and the eye's receptors for red are located in the center, which will produce the sharpest image, making it a natural choice for the warning. Red also has the longest wavelength of any of the colors found in the rainbow, meaning that the human eye can see it from a far greater distance than other colors. Because of these scientific factors, red was the obvious choice for "stop," as it allowed for plenty of time for a train to slow down.
Green, however, was initially chosen for a different purpose than "go." If a train conductor saw a green light, it meant "proceed with caution," whereas a plain white light meant "full steam ahead." But various accidents made it clear that plain white wasn't the best choice. There are stories of conductors who mistook the white stars in the sky and other lights unconnected to the train line as a sign to proceed, causing many possibly avoidable mishaps. In time, plain white lights were eliminated from the warning system entirely and green was reassigned to mean "go."
In terms of visible light, green falls roughly halfway on the spectrum between red and violet. That means it's still visible from afar, though not quite as far away as red. This makes green the ideal color for "go," as a driver can still see it from down the road, but there's no need for extra time to stop or react quickly. Yellow and orange fall between red and green in terms of visible wavelength, making those colors the perfect choice for alerting people to proceed with caution.
In 1935, the Federal Highway Administration standardized the three-color system for traffic lights across the country to lessen intersection confusion. That act helped hammer home the idea that green means "go" and red means "stop," which remains a widely accepted truth today. |
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