For nearly half a century, taxes on gas and diesel fuel funded what Congress spent from the Highway Trust Fund on roads, bridges and, after a 1982 compromise, mass transit.
For the past decade, however, better mileage for cars and trucks and slower growth in the number of miles Americans traveled combined to produce less revenue than Congress voted to spend.
The current five-year transportation law, which expires in September 2020, covered that shortfall by transferring $70 billion from the general fund. To spend similar amounts from 2021 through 2025, Congress would have to find an extra $17 billion to $23 billion a year, or $94 billion over five years, according to the Congressional Research Service.
And that’s to maintain a spending level that is inadequate, according to business and transportation advocates, many lawmakers and, at times, President Donald Trump.