By Keith Laing - 06/21/12 03:43 PM EDT
The Senate proposed a package of tax loopholes and fee increases it said would generate most of the difference, but the group of lawmakers lobbying to protect the land and water conservation funds said the upper chamber opted to steer clear of the trust fund.
The House originally proposed paying for the difference with increased domestic oil drilling, though the lower chamber's proposal for a five-year, $260 billion measure struggled to win support from conservative Republicans in the chamber.
The highway conference committee has until June 30 to reach an agreement on a transportation bill before the scheduled expiration of the current mechanism for funding road and transit projects. The government's authorization to collect the gas tax is also included in the transportation bill.