Why are stoplights Red, Yellow and Green?

为什么交通信号灯采用红、黄、绿色？

Stoplights are red, yellow, and green, because traffic officials, early on copied the code system railroad engineers devised for track systems controlling the trains.
　　

交通信号灯采用红、黄、绿三种颜色，是因为早期的交通指挥官模仿铁路工程师所设计的用于铁道系统控制火车的编码系统。

The goal of the railroad engineers in crafting this code was to prevent often fatal train collisions, by giving the trains advance warning. Therefore they did not take their task lightly in selecting the symbolic colors for the signals.
　　

铁路工程师设计这一编码系统的目的是为了通过给火车发出预光警告防止经常发生的致命火车相撞事故。因此，他们在选择信号的象征性颜色时决不能掉以轻心。

Red, the color of blood, proved a logical choice for the stop signal, as for thousands of years, this color forbade danger. The color alone, railroad engineers reasoned, should give people cause to pause, to abide by the signal, and to stop or suffer the consequences of death and destruction.
　　

红色，血的颜色，作为停止信号，是一种合乎逻辑的选择。几千年来，红色预示着危险。铁路工程师们推断，红色本身就提醒人们暂停，或呆在该信号旁边，或停止前进，否则将会遭受死亡或损毁的后果。 　　

Engineers used the trial and error method in selecting the other colors. The first trial in the 1830s, that of choosing green for the caution signal, and clear for the go signal, failed miserably. Clear as a choice for the go signal, varied slightly from the light cast from typical street lamps, or from the glare of the sunlight, and, thus could quite easily be mistaken for the go signal...after the fact.
　　

工程师们在选用其他颜色是采用了反复试验、不断摸索的方法。第一次试验是在十九世纪的三十年代。起初他们选择绿色作为“注意”信号，明亮作为通行的信号，结果遭到惨败。用亮灯作为通行信号，其明亮的灯光跟一般街头的路灯差别不大，跟太阳光的闪烁差别也不大，路灯及太阳光都可能被误认为是通行信号。

This failure prompted the railroad engineers to alter their color selections to red for stop, green for go, and yellow for caution. Traffic engineers, either lacking in ingenuity or a work ethic, scurried off with this system of color coding, and instituted the very first electric stoplight in Cleveland, Ohio in 1914. The first signal did not include the color yellow for caution, but that was later added within a few years. Railroad engineers, not traffic engineers, should be credited for the lives saved in the interim, by their system of coding warning signals red, yellow, and green.
　　

这一失误提醒铁路工程师们将信号灯颜色的选择改为红灯停，绿灯行，黄灯“请注意”。而交通管理工程技术人员有些由于缺乏机灵，有些缺少职业道德而匆匆离开这一岗位。这种交通信号灯编码系统于1914年在俄亥俄州的克利夫兰市首次实行。第一次信号中不包括用于“注意”的黄色，黄色是以后几年内后加的。因为铁路工程技术人员，而非城市交通工程技术人员发明的红、黄、绿三色编码预警系统挽救了在瞬间可能发生事故的许多人的生命，他们的功劳是不可磨灭的。

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