Well .... that depends on what you are doing. I guess that your cars are driving round a grid, a bit like Sim City ?
One way might be to (say) set them off using a bullet - on collision with an intersection graphic you can look at where it can go, and pick a good direction , occasionally randomising it a bit otherwise it would go round in circles.
It really depends. If (as in Sim City) it is purely graphic fluff, something simple - if it is a core part of the game, say you have to build the layout so traffic moves without getting stuck, you might want to spend a lot more time on it
As I said, it depends on what you are actually doing.