"The downside is that such a transportation system would give the government at least the capability to exert increasing control over when, where, if--or for how much additional taxation--people are allowed to go places in individually owned vehicles. It could also give government the ability to track where people go and when."
Heh. "Downside". Given the NSA revelations and our government's desire for wealth transfer, it's not too close to a tinfoil hat to say that the primary objectives are taxation and data logging.
Apropos of nothing, here are some videos we should all watch and think about:
Conclusion: people are smart. This program would be a colossal waste of money for the government to try and implement. Sure, harsh penalties for tampering with the installed device on the vehicle would be written into some law. Countermeasures such as those above will probably be outlawed.
But here's the thing-proving you tampered with a signal is very difficult to do. Just too much plausible deniability.
Doesn't mean the government won't try.