Yet another reason to stop building new interstates...

...that bank account is empty:

The Highway Trust Fund could fall short more than $4.29 billion in fiscal year 2009, a Treasury Department economist told a gathering of transportation experts Sept. 25, but said the "most likely" outcome would be a shortfall of $110 million.
Richard Prisinzano, economist at the department's Office of Tax Analysis, said increased fuel efficiency and rising gas prices have caused a slowing of growth in highway-related excise taxes since 2003.

"The trust fund has a bleak outlook," Prisinzano said during the annual gathering of the American Highway Users Alliance. "People are doing less driving."