One of them is in Dillsburg, Pa. It's been shut down — but it won't get fixed for five years. State Transportation Secretary Allen Biehler says he has 6,000 other bridges in line for repairs.
"Those bridges are an average age of 50 years old, and that's about what a bridge's life is, in using older designs," says Biehler.
New York's Tappan Zee Bridge is over that age limit. Engineers say the major Hudson River crossing leading to New York City desperately needs a $1.3 billion overhaul.
"It's unbelievable the amount of traffic we experience in this country," says Robert Bernstein, CEO of Material Technologies, whose company specializes in technologies that monitor metal fatigue in real time. "It's much more than 50 years ago. Plus, what's going over them is 10, 20, 30 times heavier."
And it's not just bridges, reports CBS News correspondent Nancy Cordes. From steam pipes to the power grid to water mains, much of the nation's infrastructure has not been adequately maintained, much less modernized. experts say. Demand has surged in the past few decades, experts say, but the will and money to fund upkeep have not.
"When you throw the switch and the power doesn't come on; when you turn your faucet and clean water doesn't come out, then you pay attention to it. That's too late," says Patrick Natale of the American Society of Civil Engineers.
The society put out an infrastructure report card in 2005. The nation's aviation system got a D+; wastewater management got a D- and dams got a D.
More than 3,500 dams are currently considered unsafe, including the largest dam east of the Mississippi — the Wolf Creek Dam in Tennessee.
"If you live downstream from a dam, it doesn't matter whether the dam was attacked by terrorists or whether it failed because of fatigue and age and lack of repair," says Natale. "The people downstream are all impacted the same."
It's estimated that the cost of updating the nation's infrastructure would be $1.6 trillion. That's about $5,300 for every American.
The cost of not updating, engineers warn, might be measured in more human lives.