Debate on the highway bill usually centers on how much money should be doled out for road and infrastructure projects sought by Members.

But next year, the politically popular legislation might take on a new twist as House and Senate transportation committee leaders must also cover a multibillion-dollar shortfall in the Highway Trust Fund.

The previous highway bill, passed in 2005, is set to run out of money in 2009, just before authorization for that legislation expires.

A plan originally drafted by Senate Finance Chairman Max Baucus (D-Mont.), ranking member Chuck Grassley (R-Iowa) and Sen. Patty Murray (D-Wash.) would have made up the shortfall by transferring $8 billion from the General Fund to the Highway Trust Fund.

The proposal was set to be attached to a bill offering a temporary extension of the Federal Aviation Administration authorization, but in a late change, House Democrats dropped the language in the face of Republican opposition.

The House was set to pass a bill Wednesday to transfer $8 billion to shore up the fund. The White House vowed to veto that bill.

Still, the House Transportation and Infrastructure Committee and the Senate Environment and Public Works Committee, the two panels with jurisdiction over federal highway programs, have held preliminary hearings and are gathering testimony from stakeholders on how to revamp funding sources for transportation spending.

Senate Environment and Public Works Chairman Barbara Boxer (D-Calif.), is working with ranking member James Inhofe (R-Okla.), Baucus and Sen. Johnny Isakson (R-Ga.) to establish principles for legislation they are calling “MAP 21” for Moving Ahead for Progress in the 21st Century.

“We hope to be able to make an announcement before Congress adjourns on the rest of our principles,” Boxer said in a statement.

Declining to lay out specifics on the bill or a time frame for its introduction, Boxer did note that her goals for the bill would focus on moving goods, clean air and consolidation of the disparate highway programs.

At a hearing Boxer chaired last month, Inhofe suggested similar priorities.

“As we begin … reauthorization discussions, my hope is that we will be able to work together to redefine the core mission of the federal highway program,” Inhofe said at the hearing.

The National Surface Transportation Policy and Revenue Study Commission, the panel created by the 2005 surface transportation law, recommended replacing more than 100 current transportation programs with 10 nationally focused programs targeting infrastructure facilities, crippling congestion, unacceptable safety consequences, missing intercity passenger rail options, underutilized transit options, environment linkages and the synergy between transportation and energy policy.

The panel also recommended public- private partnerships to help raise money as well as an increase in the federal gas tax, between 5 cents and 8 cents per gallon over five years, to fund construction and maintenance projects.

In the House, Transportation and Infrastructure Chairman James Oberstar (D-Minn.) could outline a bill by late fall, but action likely won’t heat up until next year. Oberstar is working with ranking member Rep. John Mica (R-Fla.) on the six-year reauthorization bill.

Early Transportation and Infrastructure Committee estimates indicate the bill will hover around $500 billion. Specific funding mechanisms to meet that funding target have not been identified, but it’s an issue that will undoubtedly spawn heated debate. Committee aides predict that negotiations on the bill will be especially tough given tight transportation budgets and a push to limit earmarks.

Key business, labor and transportation groups have already kicked off a lobbying campaign to urge lawmakers to invest in a national transportation infrastructure plan.

Joining under the banner of the Americans for Transportation Mobility Coalition, groups — including the U.S. Chamber of Commerce, the Laborers International Union of North America, and the American Road and Transportation Builders Association — are pushing increased funding by increasing the gas tax and public-private partnerships.

Terence O’Sullivan, president of the laborers’ union, said those partnerships would be part of the solution but not the only option.

Although the political climate for calling for an increase in the federal gas tax seems unfavorable, O’Sullivan said they have to “look at any and every option and that certainly includes” the gas tax.