Green transportation advocates are pressing Congress to refuse any new spending that’s not tied to reform of the existing system — a call that influential senators in both parties ruled out today.

Senate Environment and Public Works Committee Chairman Barbara Boxer (D-CA) joined Sen. Jim Inhofe (OK), the panel’s ranking GOPer, in endorsing another 18 months of the 2005 transportation bill.

The extension, Boxer said, should be "clean as it can be, clean as a whistle … not with these policy changes, because it will in fact jeopardize a quick passage of this extension."

Boxer’s agreement to an extension free of policy reforms appears to be an acknowledgment that Inhofe and most other GOP senators would slow down approval of the short-term transportation measure. But she faced a lone critic today in Sen. George Voinovich (R-OH), who challenged Boxer to back down from her opposition to raising the federal gas tax during an economic recession.

"I will tell you that if you go out to the people of America
and say [a gas tax hike] is the solution, they’re not going to buy it,"
Boxer said.

Voinovich reminded the Californian that she "is always talking about the environment; [drafting a new transportation bill] is going to have a huge impact on greenhouse gas emissions." He suggested that senators "look at" the House transportation bill offered by Rep. Jim Oberstar (D-MN) and pitch the American public on an increase in the gas tax, which has remained static since 1993.

In fact, recent polling supports Voinovich’s argument, not Boxer’s. A survey released earlier this year by the advocacy group Building America’s Future found that 81 percent of Americans would pay more in federal taxes to support infrastructure investments.

But the alignment of Boxer and Inhofe, as well as Sen. Max Baucus (D-MT) — whose Finance Committee must agree on a revenue source for the next transportation bill — in favor of a clean 18-month extension is enough to doom the House effort to pass a bill this year.

Boxer described the process as a "two-track effort," promising to work on a "transformational" long-term transportation bill during the 18-month extension period of the existing law.

Given Congress’ full plate and Boxer’s focus on climate change legislation, however, the chances of passing a broader six-year transportation bill before 2011 look slim right now.

Late Update: Boxer closed the hearing by asserting that the lack of a revenue source for a new transportation bill, not the crowded congressional calendar, is driving her support for a "clean" 18-month extension.

"For those who want to focus on transformation, I urge them to work with me on my global warming bill," which will have a transportation portion, she said.