What are more diffuse - the benefits or the costs of roads?

It seems to me the benefits, right? Depending on the financing perhaps they might be equal, but probably the benefits.

Another thought - it seems to me we should think a lot about the relative impact on a politician's prospects of tax cuts, spending increases, and debt. Does anyone do this sort of analysis? It seems to me everywhere I turn I see discussions about how politicians like the opportunity to spend money, and that to me sounds like a really sloppy way of doing public choice theory considering the government's budget constraint.

And yet another thought - the government's budget constraint is as hard as anyone else's because like anyone else's a budget constraint is an accounting identity. When people say that governments face "soft budget constraints" what they mean is that they can rely on debt (although that's nothing unique to government budget constraints) and money creation (and it's not even clear how that should be in there since that isn't principally done by the fiscal authority). This gives a false impression, I think, because it provides a misleading view of what politicians are actually doing. They have a hard budget constraint, they have a political constraint, and the objective is a little fuzzy. Most expositions of public choice theory seem to treat the budget constraint as a wild card, only a treat a portion of the political constraint, and are probably more realistic than most people on the objective function (although "realistic" can turn into "jaded" sometimes, and some of the naïve macroeconomists' objective function might be more useful).

If none of this is ringing any bells or doesn't mean anything to you don't worry about it.