Collapse Spotlights Weaknesses in U.S. Infrastructure

"It's the number one killer of bridges," he said. "If you create a hole around the bridge support, then the foundation cannot carry the load of the deck."

Vigilant inspections can prevent failures, and the Minnesota collapse was particularly shocking to those who say safety has been improving.

"By and large, things are positive, and states have been spending more on bridges and making progress," said Alan E. Pisarski, author of "Commuting in America," who noted that the number of structurally deficient bridges in the country has declined in the past decade. "But there are still a lot of them that are structurally deficient."

Nevertheless, the overall national infrastructure is stuck in a "death spiral," as states repeatedly fail to maintain the status quo condition of their transportation networks, Pisarski said. Maintenance standards slip further as the money is spread thin.

Diminishing tax revenue and surging costs have put a double squeeze on state transportation departments, transportation experts said. While federal gas tax rates have remained at 18.4 cents a gallon since 1993, construction costs have been increasing 20 percent a year in some areas. The price of steel, oil and concrete are all up, partly driven by demand for raw materials in China, where the government is busy laying out a national highway system of its own.

"We're going to run out of capacity pretty quick, and that is going to put a grinding halt on productivity, profitability and our way of life," said Janet Kavinoky, director of transportation infrastructure at the U.S. Chamber of Commerce.

Last year marked the 50th anniversary of the Interstate Highway System, a legacy of President Dwight D. Eisenhower and his grand vision for a road system that would shrink the continent and "meet the demands of catastrophe or defense, should an atomic war come."

The missiles never came, but the cars did. State transportation departments, which took control of the interstate system in exchange for federal funds, are confronted with an even costlier mission: satisfying commuter demand for lane-widening projects in urban areas where land is most expensive.

One result, said the Reason Foundation's Poole, is that states are turning to the private sector to maintain existing roads and build the next generation of highways, a change encouraged by the Bush administration.

Jerome F. Hajjar, professor of structural engineering at the University of Illinois at Urbana-Champaign, said the American Society of Civil Engineers has been warning for years that the nation needs to devote more attention to its aging bridges.

"Each bridge is different, and each bridge needs to stand up," he said. "Collapsing is not an option."

Staff writers Brigid Schulte and Amy Goldstein contributed to this report.