程序实现的功能：

1.东西方向车辆放行30秒钟。即东西方向的绿灯和南北方向的红灯同时点亮30秒钟； 2.30秒钟后，东西南北四个方向的黄灯闪烁3次，闪烁频率为0.5秒，以警示车辆将切换红绿灯；

3.四个方向的黄灯闪烁3次后，转为南北方向放行30秒钟。即东西方向的红灯和南北方向的绿灯同时点亮30秒钟；

4.南北方向放行30秒钟后，转为东西南北四个方向的黄灯闪烁3次，以警示将切换红绿灯；

5.四个方向的黄灯闪烁3次后，再转为东西方向车辆放行30秒钟。如此循环重复。-Program implementation functions:

1. East-west traffic release 30 seconds. What direction is north-south direction of the green and red lights lit for 30 seconds at the same time　2.30 seconds, four directions of East and West 3 flashing yellow light, blinking frequency is 0.5 seconds, to alert vehicles to switch traffic lights　

3. The yellow light flashes four directions 3 times, 30 seconds to release North-South direction. What direction is north-south direction of the red and green light at the same time 30 seconds　

4. North-south direction of release after 30 seconds, the four north-south direction to what the yellow light flashes 3 times to alert the traffic light switch　

5. The yellow light flashes four directions 3 times, then released into east-west traffic for 30 seconds. So the cycle repeated.