The House just approved its short-term fix for the nation’s highway trust fund by a vote of 363-68 … but something happened on the way to the floor: What began as a $5 billion rescue became a $7 billion one.

As CQ reported this afternoon, the extra money was added at the behest of the Senate, where negotiators insisted on giving the trust fund the amount that U.S. DOT officials say will keep it solvent until October.

The trust fund runs largely on revenue from the federal gas tax, which has dwindled in recent years as Americans buy more fuel-efficient cars and drive less. The White House continues to push for an 18-month extension of existing transportation law, requiring a trust fund rescue in the neighborhood of $20 billion to keep road programs going until 2011.

But House transportation committee chairman Jim Oberstar (D-MN) continues to resist the Obama administration on the issue. Oberstar voted for this afternoon’s revised legislation while characterizing it on the House floor as "an infusion, not an extension," suggesting that he has not given up on his fight for a new long-term bill this year.