设计一个交通灯，在正常情况下指挥一个十字路口的交通，有红黄绿三种状态，每次绿（红）

灯为三十秒；拥有紧急情况按键，此时相应的道路将一直为绿灯，另一条路则为红灯。 -Design of a traffic light, to commanding a crossroads of traffic under normal circumstances, red yellow and green three states, each green (red) lights for thirty seconds　has emergencies keys, the road will remain for the green light the other way as compared to the red light.