The two main sources of state transportation money are falling precipitously this summer as Americans cut back on driving, threatening to delay or halt crucial work on roads, rails and bridges and breeding an election-year issue for Congress and the presidential candidates.

Both the federal Highway Trust Fund and state road funds rely on federal and state taxes collected on each gallon of gasoline, but revenues are dropping because people are not buying as much gas now that prices top $4 a gallon. The slippage exacerbates a looming crisis with the $40 billion federal highway fund, already projected to run out of money before the start of the next budget year Oct. 1.

Even before oil prices spiked, many states were struggling to finance a backlog of highway and transit projects. Now, not only are states' share of federal road dollars in danger of running short and their own gas tax revenues falling, but they also are paying record prices for petroleum-based materials for building and maintaining roads and bridges. Virginia officials are spending $688 for a metric ton of asphalt this summer, up 272 percent in five years.

"I've never seen a perfect storm like this," said Jack Basso, who has spent 43 years as a federal transportation official and a top executive at the American Association of State Highway and Transportation Officials (AASHTO).