Roads need only be a monopoly if you can’t think outside the box. What is a road really? It can be thought of as property used for travel. There is nothing about it that says it has to be above ground, or even on the ground.
Roads run by a monopoly government are unsafe and inefficient. They are bumpy, feature no car-to-ground interface, and have thugs with lights on the tops of their cars that will run you off the road if you do not follow their diktats.
Think of all the time wasted sitting in front of a steering wheel. How difficult would the construction of smart roads be, ones that communicated with cars to tell them the position of the lanes and other cars, and then automate the driving?