交通灯信号控制器用于主干道与支道公路的交叉路口，要求是优先保证主干道的畅通。因此，平时处于“主干道绿灯，支道红灯”状态，只有在支道有车辆要穿行主干道时，才将交通灯切向“主干道红灯，支道绿灯”，一旦支道无车辆通过路口，交通灯又回到“主干道绿灯，支道红灯”的状态。-Traffic signal controller to the main road intersection with Bypass Road, requested a priority to ensure the smooth flow of trunk road. Therefore, usually in the "main road the green light, red light sticks Road" status, only the branch to walk through the trunk of vehicles Road Road, the only traffic lights will be cut to the "trunk road red light, green light sticks Road", once the branch is no other road vehicles through the intersection, traffic lights returned to the "main road the green light, red light sticks Road," the shape