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。