Good article on that
That Winning Bid for California’s High-Speed Rail: Is It Suspiciously Low?
http://www.theatlantic.com/politics/archive/2014/12/that-winning-bid-for-californias-high-speed-rail-is-it-too-low/383737/
and I love the last paragraph
“[And, yes, I have asked Richard whether the exact winning bid (look at it again, 1,234,567,890) is serendipitous, engineered to come out that way, a bit of whimsy, etc.]”
That is how it’s done. You underestimate the costs and the ridership for political reasons, and then you apply the Law of Moses when it all comes crashing down, and you look for that financial white knight.