I have made a tour around San Francisco driving the famous Citroen 2CV and using mostly roads and any available tracks on FlightGear. I started from San Francisco airport and drove until I reached the famous Golden Gate Bridge. Here are some picture...

So, it is possible to have some kind of tour and it is very funny ! Somehow, you must avoid driving on some kind of terrains which will completly block you. Try to stay on roads and on city textures. The slope of the terrain may also slow you down so you have to pay attention to your navigation !