This Thursday, Sept. 12, 2013, photo shows rust on the underside of the Chestnut Street Bridge in Philadelphia. The bridge is on a Pennsylvania Department of Transportation list of 577 bridges that both lack backup protection against collapse in case a single, vital component fails and are designated by inspectors as being in need of repair.
WASHINGTON — The United States has so many bridges in need of repair or replacement, and so little money to do the work, that state and local officials say they are engaged in a kind of transportation triage: They fix the most important and vulnerable spans first, nurse along others and, when there's no hope, order a shutdown.
Many of today's aging bridges carry more vehicles than they were originally expected to handle; truckloads that pass over are much heavier, too. Many also are years past their designed life expectancy.
They are expensive to fix and far more costly to replace — sometimes billions of dollars for a single bridge.
Of special concern are bridges that are both "fracture critical" and "structurally deficient." A bridge is deemed fracture critical when there's no backup to protect against collapse if a single key element fails. Structurally deficient means it is in need of rehabilitation or replacement because at least one major component has advanced deterioration or other problems that lead inspectors to deem its condition poor or worse.
An Associated Press analysis of 607,380 bridges in the most recent federal National Bridge Inventory showed that 65,605 were classified as structurally deficient and 20,808 as fracture critical. Of those, 7,795 had both red flags.
"Those would be ones you'd worry about more," said Ted Zoli, chief bridge engineer for HNTB Corp. in New York.
Officials say the bridges are safe. And despite the ominous-sounding classifications, engineers say that even bridges that are structurally deficient and fracture critical should not collapse if monitored and maintained properly.
"We have a term for unsafe bridges, and that is 'closed,' " said Massachusetts State Highway Administrator Frank DePaola.
The AP focused on the bridges that fit both criteria. Together, they carry more than 29 million drivers a day, and many were built more than 60 years ago. Located in all 50 states, as well as Puerto Rico and the District of Columbia, they serve communities of all sizes, and include crossings on low-travel rural roads and busy spans like the Brooklyn Bridge in New York, the Main Avenue Bridge in Cleveland and the Frederick Douglass Memorial Bridge in the nation's capital.
Finding the money to finance repairs or replacement remains a critical issue.
After the collapse six years ago of the Interstate-35W bridge in Minneapolis, state lawmakers raised the Minnesota gas tax to finance a 10-year construction program for the most serious problem bridges. Some $1.2 billion has gone into the effort so far, according to the state Department of Transportation. The campaign has helped to cut the state's original list of 172 problem bridges roughly in half.
In Maine, the I-35W collapse also prompted the state Legislature to approve extra funding of $40 million a year over four years. Maria Fuentes of the Maine Better Transportation Association said the state is plagued by older bridges and funding shortfalls, which are greater now that the supplemental funding program has ended.
"We do well with the money that we have, but we're getting to the point where if there isn't an influx of money, we're kind of rolling the dice," she said.
Mike Vehle, a Republican state senator in South Dakota, said everyone "wants good roads and bridges. No one wants to pay for it."
"We have a funding problem," agreed Dennis Heckman, the state bridge engineer for the Missouri Department of Transportation. Still, he said, motorists "should not be afraid to drive across the bridge."
His words echoed assurances given by state transportation officials across the country: Careful inspections are conducted regularly, they said, and when warranted, the frequency of checkups is increased. Also, when necessary, weight limits are placed on bridges.
The number of bridges nationwide that are both structurally deficient and fracture critical has been fairly constant for a number of years, experts say. But both lists fluctuate frequently, especially at the state level, since repairs can move a bridge out of the deficient categories while spans that become more dilapidated can be added. There also is considerable lag time between when state transportation officials report data to the federal government and when updates are made to the National Bridge Inventory.
Finding money to replace structurally deficient and fracture critical bridges in rural areas is especially difficult. Light traffic tends to make those bridges a low priority even though they may be keenly important to people in the region.