Campaign contributions are skewing the amount of federal money spent to repair the nation's deteriorating bridges, according to a new report by the U.S. Public Interest Research Group.

The group looked at earmarks in the final 2008 federal transportation appropriations bill and found that only 74 of 704 unauthorized expenditures went to repairing brides, tunnels or overpasses. It says one in ten of the projects, and about ten percent of the funding, focused on fixing the nation's crumbling infrastructure. The majority of the $570 million went for new highways and other new construction.

U.S. PIRG puts the blame squarely on campaign donations from special interests. "We believe that transportation spending is skewed toward road-widening and new highway projects favored by developers, road builders and the other interests who make those contributions," said the report's co-author, Lisa Gilbert, in a statement.

It's worth noting that Congress spent a total of $9.7 billion in the 2008 transportation bill. Lawmakers put $1.7 billion into the Capital Investment Program which uses a formula to grant money to states for road and bridge maintenance. Another $4.3 billion went to transportation grants to urbanized areas.