Lawmakers have long seen this day coming. Though a number of states have recently raised fuel levies for themselves, the federal gas tax hasn’t budged since 1993—pump-handlers have sent 18.4 cents per unleaded gallon to Washington, D.C., for more than 25 years. That’s left the highway trust fund increasingly strapped, for a few reasons. First, inflation has weakened the purchasing power of those tax dollars. Second, the cost of labor and materials to build and maintain roads and rails has spiked. And third, Americans have been driving relatively more fuel-efficient vehicles (though those climate benefits are being wiped out by the rising number of cars on the road). That translates to fewer tax dollars relative to the number of miles (and amount of wear) drivers are putting on the roads.