Given the level of efficiency and accident prevention that an automated network would bring? I don't see the government ignoring something that valuable. They're stupid, but they're not that stupid.
That would cost a ton of money. They're cheap, and they are that cheap.
I don't think it would ultimately cost that much at all. It's reliant upon computers, which are cheap and getting cheaper all the time. That's probably the only reason we don't have one already.
I think you'd see a lot of resistance because it's surrendering control. A lot of people are not going to be comfortable with the notion of climbing into a car that a computer is driving. Even though the computer is almost certainly a better driver than they are. Probably would be best received in large cities, where people are already plenty used to transit systems where they're not driving (subway, bus, taxi, etc.) Outside of the mega-metros, it's a tough sell.
I *do* remember a proposal one time (or maybe a Popular Science article or something) of creating these high-powered car carriers for the interstate system. So, say you're starting in Raleigh, NC. You drive your car up onto the carrier, and when it's loaded, it screams off down I-40 at 100mph or more in a dedicated lane, then stops at each major city between here and California. So when you get to the closest stop to your final destination, your car is unloaded and off you go. You'd pay based on how far you rode on it, kind of like a toll highway. And the cost would ideally be less than you would have spent in gas by driving it yourself. Plus, instead of a grueling 8-hour drive to Memphis, you can kick back and sleep or read or even grab a bite to eat. It's kind of a "road train". I think it never happened because the carrier would need to be huge to achieve the necessary economy of scale to make it viable, the kind of engine you'd need wouldn't be fuel efficient, and the roads simply aren't built to handle a behemoth like that.