And 83% of the infrastructure spending will achieve only 17% of the net benefits

Marginal Revolution:

Peter Orzag, President-Elect Obama's choice for OMB estimated - when Director of the CBO - that an additional $20 billion in spending, mostly to maintain current transportation infrastructure, would achieve 83% of the net benefits to be had from more transportation infrastructure spending.  Moreover, in many cases, congestion pricing would be both greener and more efficient than greater spending.