I have to be careful about using the word "subsidy" -- as in crony capitalism. There may be explicit cash transfers or there may be political favors (or both). In the process of land development and the ever more complex "approvals process", the latter can be signficant. This is typically the case for "transit oriented development".
But the most interesting U.S. case to study in the TOD field has to be New York city. And if researchers have time series data for many small local geographic areas, that is as good as it gets.
David King pointed me to his recent paper which addresses all these points. He is interested in the chicken-and-egg question involving land development and the opening of subway stations. Here is the abstract. I learned a lot reading his paper. The author notes that, "the [NY] subway system was substantially completed in the absence of substantial competition from autombiles" (p. 30). Planners take note.