Jefferson City -- Missouri's highway funding has hit a pothole.

The director of the Missouri Department of Transportation said Wednesday that its tax revenues are running 4.9 percent behind projections through the first four months of the fiscal year -- a trend that could jeopardize future road and bridge projects.

The department plans to cut down on its grass mowing, leave staff vacancies open and reduce overtime expenditures. But construction delays could be necessary as soon as the 2010 fiscal year, which starts in July 2009, if tax revenues don't pick up from fuel and vehicle sales, said department director Pete Rahn.

"Obviously, we're going to do everything we can to prevent that, but that is a possible result," Rahn said. "These aren't great times."

Rahn raised concerns while presenting an annual report Wednesday to the Legislature's Joint Committee on Transportation Oversight, and he elaborated in a subsequent interview with The Associated Press.

The slumping tax revenues are largely a result of the struggling economy in which people are buying fewer new vehicles and trying to stretch each gas tank a little further before a fill-up.

But the revenue shortfall is made worse because it comes just as highway bond repayments are forcing a significant decline in the amount of money available for construction.

Last year, the department's bond-enhanced budget for road and bridge construction was $1.3 billion. That dropped to about $850 million this year and is expected to fall to about $565 million next year.

Besides federal revenues, Missouri gets much of its highway money from state motor fuel taxes, driver's and vehicle license fees and sales taxes on vehicle purchases.

Fuel taxes were projected to decline this year but have done so at a greater rate than expected. License fees have come in slightly ahead of projections. The biggest concern, Rahn said, is that vehicle sales taxes are 11.3 percent below projections.

"The dearth of sales from auto dealers is telling us that that number is probably going to get worse," Rahn said.

So far, the department's state tax revenues are about $18 million behind projections. That shortfall could grow to about $73 million by the end of the fiscal year next June, Rahn said.

Missouri's road construction program could face additional pressure if the department needs to spend more to shore up its employee retirement system, which has been hit by stock market declines, Rahn said.

But he remains optimistic that Missouri could get some help from the federal government.