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We have been taught from a young age that red means stop and green means go. So why were these colors chosen for traffic lights? And what’s the history behind the colors?

To trace the connection between the colors and traffic lights,we have to travel back in time to the earliest railroad signals (信号灯) developed in the 1830s. Those first railroad signals were the forerunner of our modern stoplights. Like modern traffic controls,they contained three lights:one for stop,one for caution (警告),and one for go. The original color system was different from our modern system,though. Red meant stop,green meant caution,and 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, long before cars were even around. Scientifically speaking,red is the color with the longest wavelength which means that as it travels,it gets spread less in different directions than other colors,so it can be seen from a greater distance.

Why green and white were chosen for the other signals remains a bit of a mystery. It’s possible that the two colors were chosen because how they contrasted (反差) with red. This system of color-coded signals remained in place (仍然有效) for several decades until it became clear that using white for go could cause serious problems. Around 1914,a train signal’s red lights broke down,causing it to appear white. As a train approached the signal,it was supposed to stop,but the driver believed the white meant go. The result was a terrible train crash. After that,the color for go was eventually changed to green.

To provide the most contrast between red and green,yellow was then chosen as the new color for caution,because it can be seen well at all times of the day. After cars were invented and went into mass production,a similar signaling system was needed to control the flow of traffic. When traffic lights were put up,it became standard for them as well.