An on-again, off-again move by the Obama administration to scrap the federal gas tax in favor of a pay-per-mile fee would boost the tab to Americans as high as 250 percent, raising their current tax of 18.4 cents a gallon to as high as 46 cents, according to a new government study.

But without a tax increase, said the Government Accountability Office study, the government’s highway fund is going to go dry. One reason the fund is going broke: President Obama’s push for fuel efficient cars has resulted in better mileage, and fewer stops at the pump.