They're hamstrung in Canada, and they were hamstrung in California (another private operator of toll lanes, and another case where nothing could be done to improve nearby roads). Unfortunately, the courts generally rule according to contract - that's why it's best to prevent this insanity in the first place.
Then you're right, it would be pretty bad news. It's a lot like the old railroad and oil trusts, governments unto themselves that would effectively jack-over and starve out entire towns until they gave up and played ball the way the trust told them to. But then, isn't that what the antitrust laws are supposed to stop?