First, a disclaimer: this is yet another one of my experimental borderline-minarchist (no pun intended) idea threads along the same lines as many other thought experiments I've started in the past (ex.
Parents Tax). It might seem like a copout to the "who will build the roads" nonsense, but it's more of a contingency plan / safety valve just in case we are wrong, so please don't call me a statist just for contemplating this. This is also more of a 19th century idea than a 21st century one, because flying cars would solve the vast majority of transportation access issues, but it nonetheless may be an idea worth considering.
Now, this idea, in its entirely, is that there are natural limits to ownership of land imposed by other people's Right to travel. Every piece of property of sufficient size must be surrounded by an "unownable" perimeter area about as wide as a modern highway. Continuous pieces of property larger than X acres must also be separated into pieces of property X acres or less by allowing such "unownable" transport corridors. Let's call those perimeter areas "open roads".
The rules of the "open road" would be analogous to other environments where property ownership is presently impossible, including air flyover rights above several hundred yards. No one can homestead this property except perhaps by buying up the surrounding property and providing a different "open road" that fits the geographic criteria of other people's Right to travel. NAP still applies, obviously, but any action that impedes other people's Right to travel constitutes an act of aggression. People may leave pieces of their property on the "open road" only when it doesn't interfere with other people's Right to travel, which means nearby residential and business interests would be interested in leaving things like pavement, electrical / communications wiring, light poles, cameras with "open source" video feeds to ensure law and order, and so on. Damaging those privately-added road infrastructure components would constitute an act of aggression against the person who left them there, or against the Rights of a subsequent traveler. A lot of the ideas of how automotive road rules can be facilitated without a centralized authority have been discussed elsewhere
(ex).