Ezra Klein via Kevin Drum asks, fairly reasonably, why with very low US borrowing rates does it not make sense to take infrastructure projects we know we have to do in the next 5-7 years and pull them forward. If we know we have to rebuild bridge X in 2016, lets do it now when there is so much construction capacity sitting around.
In an idealized Platonic technocratic world that many Lefists still insist on believing we actually live in, trustworthy and knowledgeable agents of the state would work up such a list and we could fund it, happy we have made a good financial decision. But we don't live in that world, as I wrote in the comments
The reason this does not fly has to do with politician's incentives and trust. In short, Democrats had their chance to do exactly this. Two years ago, nearly a trillion dollars of such stimulus was approved and sold to the American people as just this sort of infrastructure spending.
But it was no such thing. Most of the money went to state and local governments as transfer and stabilization payments to keep unionized government workers, who are reliable Democratic voters, employed. Congress and the Administration knew that the majority of the public would have been leery about spending it this way, so it was sold as "infrastructure" despite the fact that less than 10%, by my count, could reasonably be called this.
Having sold a trillion dollars of pork, waste and political payoffs as "infrastructure," you should not be surprised that the American public is reluctant to believe that an infrastructure project that just pulls future necessary spending forward is really any such thing. You have in short blown your trust, which is amazing given just how much of a mandate Obama entered office with. Note that this is not narrowly a criticism of Democrats, they just happen to be in charge. No one would trust Republicans either.
And by the way, it takes years to really get infrastructure projects up and running - the environmental reviews and red tape that most of the readers for this site have advocated in favor of for years causes these things to take forever. Not to mention the engineering and procurement. Even Obama has admitted that he did not understand that shovel-ready was no such thing, even though many of us warned of exactly this problem the first time around
The money is only "free" in a relative sense if we know we have to spend it anyway in future years. It is not at all free if we have to take it from some productive private use and redeploy it for some politician's whim that gives him or her a nice bullet point on their re-election web site. Unfortunately, in the real world we live in, rather than in the technocratic paradise Klein imagines, any such bill will be larded with just such flights of fancy from powerful representatives of both parties.
Update: Talk about history repreating itself, here is what I wrote in January of 2009.
The infrastructure piece, despite being less than 10% of the bill, allows politicians to call this “investment” and “green energy” and “infrastructure” which sell better with sections of the public than “welfare” and “transfer payments.” The minority infrastructure pieces allow Congress and Obama to call the bill new and forward looking, rather than the imitation of 1970s legislation that it really is.