Minnesota officials were warned as early as 1990 that the bridge that collapsed into the Mississippi River on Wednesday was "structurally deficient." But they continued to follow a strategy of patchwork fixes and inspections, raising questions over whether the collapse could have been prevented.
"We thought we had done all we could," state bridge engineer Dan Dorgan said Thursday at a news conference held not far from the accident site.
"Obviously something went terribly wrong."
Divers, meanwhile, continued to sift through huge chunks of concrete and twisted metal in the Mississippi River. Emergency workers shifted their focus Thursday from searching for survivors to recovering bodies.
Four people have been pronounced dead from Wednesday's collapse, but police say more bodies remain in the water. Hospital officials say 79 others were injured.
Officials said a strong current and low visibility hampered the search, but a "number of vehicles that are underneath big pieces of concrete" had been located with sonar.
"We do know we have some people in those vehicles," said Police Chief Tim Dolan on Thursday. "We know we do have more casualties at the scene."
Extracting the vehicles involves moving around very large, heavy pieces of bridge, and the operation was expected to take several days.
The collapse happened shortly after 6 p.m. local time during the height of rush hour, sending a massive cloud of dust into the sky and terrifying onlookers during the height of rush hour.
Four lanes were open on the eight-lane Interstate 35W bridge at the time, while two pairs of outer lanes had been closed to repairs.
Dozens of cars fell more than 60 feet into the Mississippi. A school bus carrying about 60 children was on part of the collapsed bridge, but the students and driver escaped without serious injuries as the bus sat on the angled concrete.
Divers on Thursday took down the licence plate numbers of submerged vehicles to help authorities track down the vehicles' owners.
The U.S. Homeland Security Department said the collapse didn't appear to be terrorism-related, but the cause was still unknown. Federal officials said $5 million would be rapidly released to help with efforts such as re-routing traffic around the disaster site.
'Structurally deficient'
In 1990, the federal government gave bridge a rating of "structurally deficient," citing significant corrosion in its bearings.
The rating means portions of the bridge needed to be scheduled for repair or replacement. And it was on a schedule for inspection every two years.
Dorgan said later inspections in the 1990s found fatigue cracks and corrosion in the steel around the bridge's joints. Those problems were repaired. And beginning in 1993, the bridge was inspected annually instead of every other year.
The "structurally deficient" rating made the 35W one of 77,000 bridges in that category across the U.S. -- with 1,160 in Minnesota alone.
The White House said an inspection of the160-metre-long, 40-year-old bridge in 2005 found problems. Transportation officials said the bridge span rated 50 on a scale of 100 for structural stability.
However, "It didn't mean that the bridge is unsafe," Transportation Secretary Mary Peters said.
Minnesota Gov. Tim Pawlenty ordered on Thursday an immediate inspection of all bridges in the state with similar designs. But he said the state was never warned that the bridge needed to be closed or immediately repaired.
"There was no call by anyone that we're aware of that said it should be immediately closed or immediately replaced," Pawlenty said. "It was more of a monitor, inspect, maintain, and potentially replace it in the future."
But White House press secretary Tony Snow earlier said while the inspection didn't indicate the bridge was at risk of failing, "If an inspection report identifies deficiencies, the state is responsible for taking corrective actions."
Witness heard 'roar' of collapse
Leone Carstens, who lives several blocks from the bridge, was at home when the collapse occurred.
"There was this roar, I guess you would call it. I walked out to the other room and looked out the window and it was gone. It had already happened," she told CTV's Canada AM on Thursday.
Melissa Hughes, 32, narrowly survived when her car dropped several feet along with the western edge of the bridge.
"You know that free-fall feeling? I felt that twice," she told The Associated Press.
A truck landed on top of her car, heavily damaging part of the roof. But somehow Hughes escaped without any injuries.
"I had no idea there was a vehicle on my car," she said. "It's really very surreal."
Workers had been conducting work recently to repair the bridge's surface. Sen. Norm Coleman, R-Minn., told CNN that the bridge had been structurally inspected three years ago and received a clean bill of health.
When still intact, the bridge rose about 20 metres above the river's surface. Between 100,000 and 200,000 vehicles per day are estimated to use the bridge.
Federal Secretary of Transportation Mary Peters spoke at a news conference Thursday, pledging engineers and experts from her department would provide full support to the investigation, and would stay on the scene as long as necessary.
"We fully understand what happened and we will take every step possible to ensure something like this does not happen again," she said.
Pawlenty said the silver lining to the tragedy is the examples of heroism, where bystanders and Good Samaritans rushed to the scene to help the victims.
"So it's in this horror, this tragedy, we see a silver lining of the goodness of the people we see in Minnesota."
