The Highway Trust Fund will need an infusion of $5 billion to $7 billion by August to avoid a slowdown in spending, Senate Environment and Public Works Committee Chairman Barbara Boxer (D-Calif.) and the panel’s top Republican, James Inhofe (Okla.), are warning.

Citing Obama administration and Dept. of Transportation estimates, the senators said on June 2 that $8 billion to $10 billion more will be needed in 2010 to maintain the current highway program level, which is $40.7 billion.

To fix the 2009 problem, Inhofe raised the idea of using the interest on the trust-fund balance. Interest is pegged at roughly $750 million a year and now goes to the general fund. Congress rescued the trust fund last year with an $8-billion transfer from the general fund.