Minneapolis counts cost of bridge's rush-hour collapse

An investigation was under way last night, looking into the catastrophic collapse of a major bridge across the Mississippi river on Wednesday at Minneapolis. The bridge was jammed with evening rush-hour traffic on Wednesday, in which 20 or more people may have lost their lives.

The official death toll was just four by yesterday evening, with 80 people injured ­ many rescued from their cars which had plunged 60ft into the river. But hopes were fading for 30 or more people still missing, some of them trapped in cars beneath chunks of concrete and twisted steel protruding from the river. A dozen divers were searching the muddy waters in which at least 30 cars are believed to lie, some containing bodies.

Initial rescue operations have now officially been redesignated a " recovery effort", an indication that authorities expect no more survivors to be found.

Tim Dolan, Minneapolis's police chief, said yesterday afternoon that " several more people are confirmed dead at the scene".

In fact, though the economic cost of the loss of a main commuting, business and trucking route will be substantial and long felt in the Minneapolis region and beyond, the scale of human disaster could have been worse. Because of routine maintenance work, only two of the four lanes in each direction were open, reducing the number of vehicles.

Miraculously, all 52 students and nine adults returning from a field trip survived when the piece of highway on which their orange school bus was travelling crashed down on to the river bank. They escaped with minor injuries. But others who lived were less fortunate. A steady stream of patients arrived at local hospitals, some unconscious and others with serious head and back injuries. One doctor said: "There was blood everywhere."

The calamity happened in an instant. One moment the Interstate 35 highway linking the "twin cities" of Minneapolis and St Paul on either side of the Mississippi was intact, the next ­ at about 6.05pm ­ the central 1,000ft-long portion crumpled, both ends almost simultaneously, with what one eyewitness described as a "a clap of thunder". Charlie Leekley, a riverboat captain whose vessel was nearby, said: "There was an eerie silence like I've never heard."

Pictures taken by a mobile phone and shown on CNN suggested the collapse started in the middle of the structure and took just seconds. As a grey-white cloud of dust erupted, cars on the bridge began skidding and sliding, before falling like stones into the water and debris. "We started hearing boom, boom, boom and we were just dropping, dropping, dropping, dropping," said Jamie Winegar, from Houston, Texas. Her husband, Dennis Winegar, tried desperately to keep control of the car: " I slammed on my brakes and saw something in front disappear. Then my car pointed down and fell."

President George Bush promised a "robust response" from the government.

As government investigators rushed to the scene, the cause of the catastrophic failure ­ the worst of its kind in a generation in the US ­ was a mystery. No earthquake, landslide or other natural disaster was responsible, and officials quickly ruled out a terrorist attack.

Reports emerged last night of previous warnings about the bridge. Minnesota's Governor, Tim Pawlenty, claimed that it had passed various checks in the past two years. But it has been found that it was among hundreds of bridges across the country deemed to be "structurally deficient" in a survey by the US government in 2005. The President's spokesman said that while inspections had not indicated that the bridge was at risk of failing, "if an inspection report identifies deficiencies, the state is responsible for taking corrective actions".

Meanwhile, the engineering and construction company URS Corp had recommended last year that the bridge be retrofitted to "eliminate the possibility of a member fracture".

Officials last night ordered inspections of the 700 bridges across the US that are similar in design to the one in Minneapolis. "This will be a complex investigation," said Mark Rosenker, the head of the National Transportation Safety Board. "It's much too early to say what happened." The NTSB intends to salvage key parts of the bridge and "reassemble them like a jigsaw puzzle", to find out what went wrong.

According to Jim Burnett, a former NTSB chairman, there are two early suspects ­ fatigue stress of the steel trusses that underpinned the bridge, and vibration. Jack hammers and drills were being used in the maintenance work. The collapse also occurred as a freight train was rumbling along the railway line along the river bank. A slab of masonry fell on one passing wagon, pinning and crushing it.

Other speculation was that dampness and humidity from the river, coupled with the bitter winter weather in the area, could have caused the steel to degrade more quickly. The single-span bridge, supported by two concrete pillars on each bank, was built in 1967 and carried 140,000 vehicles a day. It underwent regular inspections in 2005, 2006 and earlier this year, and although deemed "structurally deficient", was not considered unsafe.

Some 70,000 to 80,000 of all the bridges in the US have a similar classification. In the case of the I-35 bridge, a decision was soon due to be taken on whether to carry out major repairs, or to replace it entirely ­ a new bridge would not have been in place until 2020.

Troubled bridges

November 1940: Tacoma Narrows Bridge in Washington, the third longest suspension bridge of its day, collapses. No one died.

December 1967: The Silver Bridge spanning the Ohio river at Point Pleasant, West Virginia, collapses; 46 people died.

June 1983: A bridge section of the Interstate 95 highway in Connecticut collapsed, due to corrosion. Three died.

April 1989: A 100ft section of Hatchie River bridge on Highway 51 in Tennessee falls after rain. Eight are killed.

October 1989: The San Francisco 'World Series' earthquake brings down a section of the Bay Bridge, killing one person. A viaduct in Oakland collapses, killing 40.