Transportation Secretary Mary Peters says the federal highway trust fund will run out of money this month.
Peters blames the shortage of funds on the high price of gasoline, which has prompted Americans to drive less. And by driving less, they use less fuel and pay less in federal gasoline tax.
At a midday press conference Friday, Peters said the agency will have to delay payments to state road and bridge projects that the federal government is helping finance.
At the same time, she wants Congress to pass legislation that includes $8 billion to help cover the shortfall.
Four times this year, Republicans in the Senate have blocked a measure that would shore up the fund.