Traffic light simulation for a crossroad

Question

Hi, after some time learning the basics of C#, I want to start a new real project. My idea is about a traffic simulation in which I have got a net of streets with traffic lights and some cars which react to the allowed velocity and on the lights. I do not want to start this project without anything planning otherwise it would get unflexible and eventually too slow. My question concerning this project is: which class structure do you would use? How to realise the relationships between the cars and the streets?