Designing a microprocessor system to control traffic lights is discussed in this post. The traffic light arrangement is as shown in the figure. The trffic should be controlled in the following manner.
Allow traffic from W to E and E to W transition for 20 seconds.
Give transition period of 5 seconds (yellow bulbs ON)
Allow traffic from N to S and S to N for 20 seconds.
Give Transition period of 5 seconds (yellow bulbs ON)
Repeat the process.