It turns out that Boston’s “Big Dig” construction project cost taxpayers much more than expected — and enormous bills for interest payments and mass transit are still rolling in.Hailed at its inception as an example of “smart government” and proof that “government can still get things done,” the project was originally estimated to cost $2.8 billion. Thanks to corruption, construction mishaps and the usual friction on projects of this kind, the project took a decade longer than planned to complete, and was said at the time (December 2007) to have cost a total of $14.6 billion.There was much shock and finger-pointing when these numbers came out, but as Boston.com reports, those cost estimates were still much too low. By the time the whole mess is finished and accounted for, this beautiful proof of governmental competence and efficiency, this magnificent testimony to the ability of big infrastructure projects to turn the US around will end up costing about twice that much: at about $21 billion, the final cost will be about seven times the original estimate — an original estimate, by the way, so large that it blew peoples’ minds at the start.Why the additional costs? Three big reasons.First, so many entities borrowed so much money for the project through so many bond issues and other measures that the cost of the interest on the various loans connected to the project was both high and hard to calculate.Second, the project went on so long that the ongoing depreciation of America’s currency inflated the cost. That’s a common problem in a country with an inflating currency. The lawsuits and regulatory blockages that drag out major construction projects in the United States today combined with the steady decline in the value of the dollar to turn what initially look like reasonable proposals into mind-boggling boondoggles.And finally, the complicated political bargaining that went into the program, balancing city transit needs with the wishes of suburban legislators and placating the greens and other lobbies tacked on all kinds of extraneous project costs. Literally billions of dollars in mass transit spending was required in order to get the core highway project approved. Those projects, too, involved lots more borrowing and therefore lots of interest costs. And those projects, too, suffered from the incompetence, corruption, NIMBY lawsuits, regulatory roadblocks and general inefficiency of government construction projects.Put it all together, and an expensive $2.8 billion dollar highway project morphs into a $21 billion regional disaster. Only there is still more to come. That $21 billion still doesn’t include up to about $5 billion of mass transit construction and interest costs, some from projects that are legally required but haven’t yet gotten underway. Some of these costs will likely go higher as well; figure about $26 billion as a likely figure.America needs infrastructure work; having driven in Boston before and after the Big Dig, I have no doubt that something of this kind was badly needed. But it’s also clear that America’s creaking “infostructure” of institutions and procedures is not up to the job of managing projects like this one.The Big Dig didn’t show that government can work; it showed just how broken our government systems are. There is a normal and irreducible friction to government work of any kind, but the mess in Massachusetts shows a system that simply can no longer execute complex projects in a timely way at a manageable expense.If California’s high speed rail project runs into the same kinds of problems — and it will, dear readers, it will — heaven only knows how much it will cost by the time the last Wall Street bank clips the last coupon on the last construction bond.The governments progressives have built can’t do the jobs progressives want government to do: that remains one of the hard core problems that is driving the blue social model to the wall.