Support for massive investments in transportation infrastructure, possibly with a change in the share of spending on transit, seems widespread. Such proposals are often motivated by the belief that our infrastructure is crumbling, that infrastructure causes economic growth, that current funding regimes disadvantage rural drivers at the expense of urban public transit, or that capacity expansions will reduce congestion. In fact, most US transportation infrastructure is not deteriorating and the existing scientific literature and does not show that infrastructure creates growth or reduces congestion. However, current annual expenditure on public transit buses exceeds that on interstate construction and maintenance. The evidence suggests the importance of an examination of how funding is allocated across modes but not of massive new expenditures.
That is from a new NBER working paper by Matthew Turner, Gilles Duranton, and Geetika Nagpal.