traffic light       
noun [ C usually plural ] uk/ˈtræf.ɪk ˌlaɪt/ us/ˈtræf.ɪk ˌlaɪt/ (US also stoplight)
A2 红绿灯,交通信号灯
one of a set of red, yellow, and green lights that control the movement of vehicles, usually at a point where two or more roads join
  The police pulled him over for failing to stop at a red traffic light. 他因为闯红灯被警察要求停靠路边。 
 Turn left at the traffic lights. 在红绿灯那儿向左转。 
 The traffic lights changed to/turned green as we approached the junction. 我们接近十字路口时,交通信号灯变成了绿色。