Well there are two types of AI road network possible. One is where the vehicles are completely self contained and autonomous in every way, and the other is one in which road sensors and other equipment creates an electronic network that keeps overall control of the vehicles (or at least one that the vehicles must report to and probably obey)
Even the "BART" trains and other so called autonomous transportation systems currently in place have to submit to human over-watch from a high-tech control room of some sort, with final override authority coming from humans in an emergency.
Since I don't see any compelling reasons that long-standing human distrust of fully automated transportation systems is going to abruptly wane, I think its safe to surmise that at least at first, such a road system will be subject to heavy human monitoring, intervention and control.
If only because some politician will demand it.
That being said, its also true that once a bureaucracy is created, it tends to self perpetuate, especially if tasty taxes can be extracted to support it.
As to unlikely scenarios....... have you met the human race?