More than 70,000 bridges across the country are rated structurally deficient like the span that collapsed in Minneapolis, and engineers estimate that repairing them all would take at least a generation and cost more than $188-billion.
That works out to at least $9.4-billion a year over 20 years, according to the American Society of Civil Engineers.
The bridges carry an average of more than 300-million vehicles a day.
It is unclear how many of the spans pose actual safety risks. Federal officials alerted the states late Thursday to immediately inspect all bridges similar to the Mississippi River span that collapsed.
In a separate cost estimate, the Federal Highway Administration has said that addressing the backlog of needed bridge repairs would take at least $55-billion. That was five years ago.
It is money that Congress, the federal government and the states have so far been unable or unwilling to spend.
"We're not doing what the engineers are saying we need to be doing," said Gregory Cohen, president of the American Highway Users Alliance, an advocacy group representing a wide range of motorists.
"Unfortunately when you consistently underinvest in roads and bridges ... this is the dangerous consequence," Cohen said of the Mississippi River bridge collapse in Minneapolis. He said engineers have estimated that $75-billion a year is needed just to keep highways and bridges from further deterioration, but that only about $60-billion a year is being provided.
A bridge is typically judged structurally deficient if heavy trucks are banned from it or there are other weight restrictions, if it needs immediate work to stay open or if it is closed. In any case, such a bridge is considered in need of considerable maintenance, rehabilitation or even replacement.
Congressional leaders say the number of bridges in need of repair is too high and the funding too low.
There is crumbling infrastructure all over the country, said Senate Majority Leader Harry Reid, D-Nev. Sen. Patty Murray, D-Wash., who heads the Senate panel that controls transportation spending, said the Bush administration has threatened vetoes when Democrats try to increase such spending.
White House deputy press secretary Scott Stanzel declined to address spending and accused the Democrats of using the bridge collapse for partisan purposes.
Democrats were not alone in calling for more bridge funding.
"People think they're saving money by not investing in infrastructure, and the result is you have catastrophes like this," said Rep. Tom Petri, R-Wis., a House transportation committee member.
The federal government is now providing about $40-billion a year to improve and expand the nation's highways and bridges.
The main source of revenue for roads and bridges, the federal highway trust fund, is failing to keep up with spending demand. The 18.3 cents a gallon in federal taxes hasn't changed since 1993, and the demand for more fuel-efficient vehicles could affect fuel consumption.
Funding isn't the only issue getting attention after the Minnesota collapse. Transportation Secretary Mary Peters said she had asked her department's inspector general to evaluate the agency's overall bridge inspections.
According to the Federal Highway Administration, most bridges in the U.S. Highway Bridge Inventory - 83 percent - are inspected every two years. About 12 percent, those in bad shape, are inspected annually, and 5 percent, those in very good shape, every four years.
The Department of Transportation's inspector general criticized the Highway Administration's oversight of interstate bridges last year. The March 2006 report said investigators found incorrect or outdated maximum weight calculations and weight limit postings in the National Bridge Inventory and in states' bridge databases and said the problems could pose safety hazards.
The Highway Administration agreed that improvements in its oversight of state bridge inspections and data were needed.
Incorrect load ratings could endanger bridges by allowing heavier vehicles to cross than should, and could affect whether a bridge is properly identified as structurally deficient in the first place, the inspector general said.
The audit didn't identify any Minnesota bridges or mention the state beyond noting that 3 percent of its bridges were structurally deficient, placing it at the low end among states. It said those bridges were crossed by an average of 30,000 to 40,000 vehicles a day, putting it 13th among the states.
How many are bad? About 74,000 U.S. bridges are rated structurally deficient. That's about 12 percent of the 607,363 U.S. bridges.
How to tell: A bridge is typically judged structurally deficient if heavy trucks are banned from it or there are other weight restrictions, if it needs immediate work to stay open or if it is closed.
Who's responsible? The Minnesota Department of Transportation was responsible for maintaining the I-35W bridge. The federal government provides most funding for construction, repair and maintenance of interstate highways and bridges, but states set priorities and handle construction and maintenance contracts.