See also - mega rail projects that start from nothing (cough HS2).

Politicians think doing engineering projects is like buying something off the shelf. Every engineer will tell you the only way to do stuff is iteration - starting small, learning from your mistakes and growing things. If you start a megaproject without a team of people experienced in doing more or less the same thing recently, it will cost vast amounts. Particularly if you push too fast and commit large amounts of money before you've had a few iteration cycles.