>No, my point is that presumably the cars arrived on your self-sufficient private roads via public roads. Is this correct or not?

Sometimes yes sometimes no.

>If everyone lived in density like yours, first of all we wouldn't have nearly anything good about modern life, but secondly yes we could obviously have the system you describe. I'll take public roads and modern life any day.

I'd say high density public roads are causing a big problems for cities. Cars are subsidized in a way that distorts the market to overrepresent car travel over private mass transit or other more efficient alternatives. I believe our cities would be much safer and more enjoyable, without losing access to needed goods, if the roads were all privatized.