This table shows Eno’s best efforts to probe how much Highway Trust Fund spending could be possible if the final surface transportation authorization bill uses the approximately $77 billion in “pay-fors” in the House-passed version of the bill and reduces the authorization period and HTF solvency window from six years to five years, as Senators are now proposing. The answer is premised on the assumption that the conferees will insist that highway spending and mass transit spending from the Trust Fund get annual spending increases at the exact same percentage rates. Under this scenario, highway and mass transit spending could get a 7.0 percent increase in FY 2016 and could then get 3.0 percent annual increases thereafter through the end of a five-year bill in September 2020. New spending obligation authority would be $27.3 billion above baseline levels over the five-year period ($20.7 billion for highways and $6.5 billion for mass transit).

All of this should be taken with a grain of salt, as annual outlays are notoriously difficult to calculate.