Readers naturally interpreted this post as a criticism of suburban development. I in fact believe that we over-subsidize suburban development through road construction, but I mainly wrote the post for two other reasons. First, it is rather obvious evidence that those who claim drivers pay the full cost of roads are wrong. And, second, there are a few central Austinites who claim that infill development actually imposes more costs on local governments than suburban development. The County's subsidy is some evidence they are wrong, and in the comments Shawn hits on some other reasons they are wrong.
The proposed bond package and its likely approval raise an interesting question: Why do central city voters -- and, for that matter, suburban voters who already have the roads they need -- vote to subsidize suburban roads? It's a puzzle if we assume voters are rational and vote according to their perceived self-interest. (I always start with that assumption rather than simply assume voters are dumb.)
It's not obvious. The bond package, because it is a true subsidy, is a wealth transfer from the average voter to a relatively small group of property owners. Subsidies like this also hurt central city property values because the improved roads make the suburbs relatively more attractive. Enticing more people to the suburbs hurts other suburbanites, too, because it puts more cars on the suburban arterials, increasing congestion.
Yet voters still vote for them.
I don't know the answer, but one possibility is that voters think population growth is good. Each new resident increases demand for doctors, dentists, restaurants, etc., which is good for doctors, dentists, restaurants, etc. Population growth is good for property owners. It is even good for downtown because it increases the pool of workers. I agree that the "Texas jobs miracle" is mostly population-driven. A larger population also sustains a greater variety of stores and restaurants.
Another possibility is the expectation of reciprocity. Perhaps there is an implied compact that I will support road subsidies for you if you support road subsidies (or bicycle lanes or parks) for me when it's my turn. I'm a bit more skeptical of this explanation but I throw it out there.
Maybe someone has a better explanation.
N.B. Note that voters don't have to believe that population growth is good per se. It might be enough if they believe that population decline relative to peer cities is bad. If that's true, then lots of road building by peers would spur more road building here.
See the comment by Jim below, however. He's got a much more sophisticated, empirical analysis.