My thoughts:
Virtual Reality and other information technologies will render physical transportation useless in about 20 - 30 years, so don’t get your hopes up about improvements to automobile engines, etc. We’ll sooner see desktop factories that can manufacture all the objects you need to get in the full-immersion VR world. I suggest checking out Kurzweil’s Singularity is Near or Drexler’s Engines of Creation. In fact, once you can define your “soul” in pure information, there would be relatively little need to physically transport it.
Anyway, in Canada there’s a private toll road that simply takes a picture of your license plate as you drive over it, and it sends you a bill. Private tollways don’t need to rely on license plates. They could use RFID, etc, to toll traffic without causing congestion.
Homesteading and private roads go hand in hand. If you have not already, read about the Least Technologic Unit, which is the homesteading concept Rothbard suggests. This would ensure roads are not unreasonably large (like they are now - guess they are contracted by lb of concrete!), so that competition has available resources. It also ensures that roads cannot extend upwards forever, which would for no good reason prevent competitors from crossing whatever 2 dimensional geometry existing roads were placed. This would allow competing roadways to be built above existing ones (although naming the grounded road the “scenic” route might prevent this - very difficult circumstances do arise).
New technology would definitely come quick. Types of vision systems that could direct traffic based upon need rather than timings (like cops often do during busy events) would become commonplace (rather than cameras designed to fine you for barely running a red light). An improvement I would expect to see would be a surveillance system, so that fault for accidents could be easily demonstrated through video.
Legally, private roads present interesting scenarios. The risk management that the state does would be now legitimate (I consider violations of liberty for risk management on public grounds immoral - licenses and traffic fines have no place unless you actually cause harm to some other driver). Private roads can be licensed differently, carry different speed limits, have these regulations enforced differently…this would allow diversity in driving conditions aligned to market demand…and could reform our ridiculous drunk driving laws - yes, there may be an option to get a drunk license.
The best reason to suggest private roads is that roads would be focused on the two objectives they should have (besides the obvious one of getting from point a to point b): lack of congestion and safety. The fastest and safest roads would be the most rewarded by the market (provided they connect at least two useful destinations).
And yes, zoning laws and other property regulation are a large means of preventing competition. Consider Disney, which has a monorail running through resort buildings. Why couldn’t there be elevated roadways extending between buildings in urban areas? There’s plenty of sky to make use of, even if the ground is already congested.