Why does green mean go？
Have you ever noticed how certain colors are associated with particular objects or emotions? For example, the color purple is often associated with royalty. If you want to express feelings of love with color, you'll probably reach for a red crayon.
What about the color green? Green is the color of the grass and the leaves on the trees. It often symbolizes life. Today, it's also the color closely associated with environmentalism. If you are environmentally conscious, then you might be part of the green movement. Instead of using fossil fuels, you might encourage others to "go green" and use renewable energy sources instead.
Speaking of "going green," it's no accident that the color green gets paired frequently with the word "go." All you have to do is stop at any intersection with a stoplight to see that "go" and green go hand in hand. But why is that?
To trace the history of the color green's connection with go, we have to travel back in time to the earliest railroad signals developed in the 1830s. Those first railroad signals were the precursors of our modern stoplights. Like modern traffic controls, they contained three lights: one for stop, one for caution, and one for go.
The original color scheme was different from our modern system, though. Red meant stop, green meant caution, and clear (or white) meant go. The choice of red for stop was fairly obvious, since red — the color of blood — has been associated with danger for thousands of years.
Why green and white were chosen for the other signals, though, remains a bit of a mystery. It's possible that these colors were chosen because of how they contrasted with red. This system of color-coded signals remained in place for several decades until it became clear (pun totally intended!) that using white or clear for caution could cause serious problems.
Around 1914, a train signal's red lens fell out, causing it to appear clear or white. As a train approached the signal, it was supposed to stop, but the driver believed the white or clear light meant go. The result was a horrendous train crash. This terrible accident revealed the dangerous flaw in the white/green/red signaling system.
As a result of the accident, the color for go was eventually changed to green. To provide the most contrast between red and green and because it's the most visible color, yellow was then chosen as the new color for caution.
After the automobile was invented and went into mass production, it soon became clear that a similar signaling system would be needed for roads to control the flow of traffic. It was only natural that the system used for years in the railroad industry would be transferred to our modern system of traffic signals for automobiles.