WASHINGTON - Motorists coming off the Frederick Douglass Memorial Bridge into Washington are treated to a postcard-perfect view of the U.S. Capitol. The bridge itself, however, is about as ugly as it gets: The steel underpinnings have thinned since the structure was built in 1950, and the span is pocked with rust and crumbling concrete.
District of Columbia officials were so worried about a catastrophic failure that they shored up the horizontal beams to prevent the bridge from falling into the Anacostia River.
And safety concerns about the Douglass bridge, which is used by more than 70,000 vehicles daily, are far from unique.
A crane removes a pickup truck from the wreckage of the Interstate 5 bridge over the Skagit River in Mount Vernon, Wash., after it collapsed in late May.
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 were both - a combination of red flags that experts say indicate significant disrepair and similar risk of collapse.
A bridge is deemed fracture critical when it doesn't have redundant protections and is at risk of collapse if a single, vital component fails. A bridge is structurally deficient when it is in need of rehabilitation or replacement because at least one major component of the span has advanced deterioration or other problems that lead inspectors to deem its condition poor or worse.
Engineers say the bridges are safe. And despite the ominous sounding classifications, officials say that even bridges that are structurally deficient and fracture critical are not about to collapse.
The AP zeroed in on the Douglass bridge and others that fit both criteria - structurally deficient and fracture critical. Together, they carry more than 29 million drivers a day, and many were built more than 60 years ago. Those bridges are located in all 50 states, plus Puerto Rico and the District of Columbia, and include the Brooklyn Bridge in New York, a bridge on the New Jersey highway that leads to the Lincoln Tunnel, and the Main Avenue Bridge in Cleveland.
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 grow more dilapidated can be put on the lists. There are occasional data-entry errors. 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.
Many fracture critical bridges were erected in the 1950s to 1970s during construction of the interstate highway system because they were relatively cheap and easy to build. Now they have exceeded their designed life expectancy but are still carrying traffic - often more cars and trucks than they were originally expected to handle. The Interstate 5 bridge in Washington state that collapsed in May was fracture critical.
Cities and states would like to replace the aging and vulnerable bridges, but few have the money; nationally, it is a multibillion-dollar problem. As a result, highway engineers are juggling repairs and retrofits in an effort to stay ahead of the deterioration.
There are thousands of inspectors across the country "in the field every day to determine the safety of the nation's bridges," Victor Mendez, head of the Federal Highway Administration, said in a statement. "If a bridge is found to be unsafe, immediate action is taken."
At the same time, all that is required to cause a fracture critical bridge to collapse is a single unanticipated event that damages a critical portion of the structure.
Signs of age are clear. The Douglass bridge, also known as the South Capitol Street Bridge, was designed to last 50 years. It's now 13 years past that. The district's transportation department has inserted so-called catcher beams underneath the bridge's main horizontal beams to keep the bridge from falling into the river, should a main component fail.
Alesia Tisdall, who drove over the bridge every day for 15 years but now crosses it only occasionally, said she found its "bounce" unnerving.
"You'd look at the person sitting next to you like, 'Did you feel that bounce?' And they'd be looking back at you like they were thinking the same thing," said Tisdallt.
Peter Vanderzee, CEO of Lifespan Technologies of Alpharetta, Ga., which uses special sensors to monitor bridges for stress, said steel fatigue is a problem in the older bridges.
"Bridges aren't built to last forever," he said. He compared steel bridges to a paper clip that's opened and bent back and forth until it breaks.
"In a bridge system, it may take millions of cycles before it breaks. But many of these bridges have seen millions of cycles of loading and unloading."