The roads only have so much capacity which is not going to change much whether the cars are self driven or not.

In London they have deliberately reduced road capacity to reduce traffic by blocking off lanes, side streets and the like. I could see a future where the normal way to get around is a self driving cab to the station at each end with a train for the main journey. I know you can do that now but the human cabs driven are kind of expensive.

Maybe something a bit like Zermatt where there is a train station and then it's pedestrianized apart from electric golf cart like taxis. It all works quite well really apart from being expensive. But property being like £1m+ is kind of a symptom of people wanting to be there.