Two U.S. senators have proposed hiking the federal gasoline and diesel taxes by 12¢ per gallon over two years and indexing the levies to account for annual inflation after that.

The lawmakers—Sens. Chris Murphy (D-Conn.) and Bob Corker (R-Tenn.)—acknowledge that their plan, which they announced on June 18,  isn’t likely to be adopted in time to patch the Highway Trust Fund’s near-term financial hole. Instead, they say they are aiming to have their plan become part of a hoped-for, long-term surface transportation reauthorization late this year.

Corker said at a press conference: “I know that we’re not going to pass this in the next month. It’s unfortunate. Our goal is to build support for this over the course of the next six months.”

Under the plan, fuels taxes would rise by six cents per gal. in 2015 and by an additionaal six cents in 2016. Annual inflation boosts would kick in after that. The senators estimate that the increases would bring in $18 billion for the trust fund over one year and $164 billion over 10 years.

To counter opposition among many in Congress to tax increases, Murphy and Corker would offset their fuels-tax increase by reducing other taxes.

One option, they say, would be to extend various expired tax breaks, including the research and development credit and the Section 179 accelerated-depreciation incentive.

But Murphy said he and Corker would “listen to other ideas” for offsetting tax reductions.

The plan drew praise from construction and engineering groups, labor unions, the U.S. Chamber of Commerce, infrastructure-advocacy organization Building America’s Future and others.

Meanwhile, the trust fund’s situation continues to weaken. The Dept. of Transportation's latest update, released on June 17, says the trust fund's highway account is projected to drop into the red sometime in mid-to-late August.

Murphy said, “There is no white knight coming to rescue the transportation fund. We can spend the next three years searching for a new, magical funding solution, but it’s likely that the best option is staring us straight in the face.”

The federal gas tax now stands at 18.4¢ per gallon. It was raised to that level in 1993, reduced to 18.3¢ in 1996 and increased back to 18.4¢ in 1997.