MINNEAPOLIS — Roughly 150 cars, trucks and at least one school bus crawling bumper-to-bumper on a bridge that suddenly crashes into the Mississippi River could have been a recipe for a massive death count.
But on Friday came what this city’s fire chief called a miraculous twist: the prospect that relatively few lives were lost.
Divers still searched through the swirling, muddy currents for cars and bodies. However, the death toll remained at six from Wednesday’s collapse and authorities cast doubt on an earlier estimate that as many as 30 people were missing. They even said it could be as few as eight.
Of the roughly 100 injured, 28 remain hospitalized and only five were critical.
“We were surprised that we didn’t have more people seriously injured and killed,” Minneapolis Fire Chief Jim Clack told The Associated Press. “I think it was something of a miracle.”
Clack cited a list of reasons: A bridge design that minimized falling debris, a quick response by rescue crews and the rush-hour crawl that gave vehicles little momentum to plunge into the river.
In addition, experts say the speed and depth of the water in the Mississippi River were much lower than normal on the day of the collapse — largely the result of a drought. That may have made it easier for people to escape the disaster.
“It’s a horrible, tragic event. But it could have been a hell of a lot worse,” said Kent Harries, assistant professor of civil and environmental engineering in the University of Pittsburgh’s School of Engineering.
'Even more treacherous'
Minnesota officials say they don’t yet know how many cars were traveling the span during the collapse. But based on the length of road, the lanes that were open, time of day and widely accepted traffic formulas, Northwestern University engineering Joseph Schofer estimated that between 100 and 150 vehicles were on the bridge.
Despite the low death toll toll, divers were still contending with a dangerous combination of sunken cars, broken cliffs of concrete and jagged rebar as they searched for bodies.
More bodies had been spotted in the fast-moving currents, which were “even more treacherous” Friday than a day earlier, Stanek said. Crews planned to focus on 13 areas on the upstream side of the collapse, including four vehicles that were partially submerged, he said.
Firefighters pulled the fifth victim, the driver of a tractor-trailer that was engulfed in flames, from the wreckage late Thursday. Video of the burning rig — nose down in the crevasse between two broken concrete slabs — was among the most compelling images shown in the immediate aftermath of the collapse. The driver was identified as Paul Eickstadt, 51, of Mounds View.
NBC reported that a sixth person, a woman, died in a hospital overnight of injuries suffered in the collapse.
Early in the day, authorities said that as few as eight people were still missing. However, they cautioned later that number could rise, in part because there was no way to know how many victims were in the water. Some people without family in the area may not have been reported missing, said Police Lt. Amelia Huffman, a spokeswoman.
The missing included a 23-year-old pregnant woman and her 2-year-old daughter who was in the back seat of the family’s car when the bridge crumbled.
Sadiya Sahal, a 23-year-old immigrant from Somalia, called her family at 5:30 p.m. saying she was stuck in traffic, said Omar Jamal, executive director of the Somali Justice Advocacy Center. That was her last phone call. “Her husband is destroyed. He’s in shock,” Jamal said.
Bridge found deficient in 1990
Authorities still do not know what caused the 6:05 p.m. collapse. Engineers had numerous theories, including heavy traffic and construction work being done on the road at the time that might have put an undue burden on the span. The bridge was deemed “structurally deficient” by the federal government as far back as 1990.
Reports indicating that problems with the bridge's structural integrity were identified years ago will likely fuel debate about the condition of the nation's infrastructure.
More than 70,000 bridges across the country are rated structurally deficient like the I-35W bridge, and engineers estimate repairing them all would take at least a generation and cost more than $188 billion.
Authorities said the “structurally deficient” tag simply means some portions of the bridge needed to be scheduled for repair or replacement. It wasn’t a candidate for replacement until 2020.
According to an analysis of federal records by MSNBC.com, few high-traffic bridges in the United States scored worse than the Minneapolis one did in its 2005 inspection.
Only 4 percent of the high-traffic bridges in the nation scored lower than the I-35W bridge in Minneapolis, according to records in the National Bridge Inventory.
Bridges are given a so-called sufficiency rating. This includes some safety elements, like structural integrity, but also weighs the bridge's size for its current traffic.
The sufficiency rating ranges from 0 to 100. A 80 score indicates that some rehabilitation may be needed, while 50 or less shows that replacement may be in order.
The I-35W bridge in Minneapolis was given a score of 50.0 in the 2005 inspection . Out of those 104,348 high-traffic bridges, only 4,227, or 4 percent, scored below 50.
First lady visits the site
Minnesota transportation officials spent another day dealing with scrutiny arising from a series of reports and inspections over the years that raised alarm about the bridge, including rust-eaten steel beams, missing bolts and cracks in the welding that held load-bearing parts together.
A consulting company that thoroughly examined the bridge noted that one possible fix — steel plating of fractures — carried a “relatively high cost,” according to a January report. Transportation officials deny that cost pressures swayed their decisions.
President Bush was scheduled to visit Saturday, and first lady Laura Bush toured the scene Friday morning. She praised the rescuers who rushed to the bridge in the chaos after the collapse — a sentiment echoed by the fire chief in explaining why more people didn’t die. Because the bridge was located near the heart of downtown, several emergency crews and residents were close by.
“We could not have done it as firefighters alone. It took more people than we had. It was organized. It was pretty calm,” Clack said.
'A lifesaving feature'
Authorities and engineers were in agreement that the truss-style design of the bridge played a big role in saving lives. The steel that supported the bridge was below the structure — as opposed to above the span in more traditional bridge designs.
“I think that was a lifesaving feature,” said Schofer. “They had this huge advantage. They weren’t crushed by steel.”
Clack said that even though the collapse occurred during rush hour, the heavy traffic was an advantage because the cars were almost stopped and didn’t have much momentum. Because of that, the collapse was less likely to hurl moving cars into the river.
“They didn’t have forward velocity,” he said, “so when they bridge fell, they went straight down.”
While the entire span covers 1,907 feet, only 458 feet is directly over water, supported by giant pylons. The rest of the bridge rises over sloping banks and tidal flats of the river channel.
The irregular slope of the riverbank on the south side of the bridge turned out to be a good thing. When that portion of bridge snapped at the middle, the support pylons held, and the roadway only had a short distance to fall until it was caught by a drop-off just before the river.
'A raging torrent'
On the north side of the bridge, however, the bank slopes down in a steady angle to a broad tidal flat. As a result, when that portion of the bridge crumpled, there was nothing to catch it.
That was evident to Dr. John Hick, assistant medical director for emergency medical services at Hennepin County Medical Center, who noticed that injuries on the north end of the bridge were much more grave.
Another factor that may have limited the death toll is the behavior of the river itself.
Mark Rosenker, chairman of the National Transportation Safety Board, said investigators were particularly interested in learning why a part of the bridge’s southern span shifted as it collapsed. That was the only part of the bridge that shifted, and it could help pinpoint the cause.
Scott Bratten, who regulates locks and dams on the river for the local district of the U.S. Army Corps of Engineers, said that because of the drought currently affecting Minnesota, the water at the time of the collapse was flowing at just a third of its normal speed.
That may have made it easier for people in cars to escape them, and it almost certainly made it easier for rescuers to make their way into the water and help the dazed and injured.
“During the spring it’s a raging torrent in there and it would be a very dangerous place,” said Whitney Clark, executive director of Friends of the Mississippi River. “The low water I’m sure was a factor in not making currents very much of an issue ... If this had happened during the spring snowmelt or something it would have been a much different situation.”
MSNBC.com's Bill Dedman, NBC News and The Associated Press contributed to this report.