MINNEAPOLIS – The new U.S. highway bridge opened in Minneapolis on Thursday, a little more than a year after the last one collapsed into the Mississippi River and killed 13 people.
A procession of vehicles led by state troopers, emergency vehicles and state highway trucks led motorists across the bridge in both directions shortly after 5 a.m. Thursday.
Traffic was heavy as a mix of cars, motorcycles, trucks and buses started streaming across the bridge. Vehicles moved slowly at first, but then picked up speed.
Many vehicles honked their horns as they drove across and a few motorists waved American flags. The major artery leading in and out of Minneapolis carried 140,000 trips a day before the collapse of the old bridge on Aug. 1, 2007, which also injured 145.
The new bridge contains hundreds of sensors that will collect a stream of data. The purpose of the "smart bridge" technology is not to warn of another impending disaster; it is to detect small problems before they become big ones, said Alan Phipps, design manager for the project with Figg Engineering Group Inc. of Tallahassee, Florida.
"What these sensors are for, it's like going to your doctor for your health checkup," Phipps said. "It's to ensure you're maintained in top shape so you never get close to having a serious problem."
The $234 million bridge was completed on budget and more than three months ahead of the Dec. 24 deadline. That means the contractors — led by the team of Flatiron Construction Corp. of Longmont, Colorado, and Manson Construction Co. of Seattle — should get a bonus close to the contract maximum of $27 million, though the actual amount has not been determined.
There also are more visible differences between the new bridge and old. The new bridge is concrete instead of steel and is built with redundant systems so that if one part fails it won't collapse. The old bridge, finished in 1967, was called "fracture critical," which meant that a failure of any number of structural elements would bring down the entire bridge.
Within the concrete of the new bridge are embedded 323 sensors that will generate a record of how it handles the stresses and strains of traffic and Minnesota's harsh climate. The data will help engineers maintain the bridge and advance the art of bridge design, Phipps said.
The sensors will measure how the bridge handles loads and vibrations and how it expands and contracts as Minnesota alternates between frigid winters and steamy summers, as well as watch for corrosion from road salt.
A system of sensors and cameras will feed data on traffic flow — including speeds, accidents, stalls and other disruptions — to a management center. Other sensors will activate an anti-icing system when necessary, and security sensors are meant to detect intruders in unauthorized areas, such as the hollow concrete box girders.
The data will feed into computers in a control room near the bridge, Phipps said. From there, engineers at the Minnesota Department of Transportation and researchers at the University of Minnesota can download it for analysis.
The National Transportation Safety Board has scheduled a hearing in November to discuss its investigation into what caused the old bridge to collapse. In January, NTSB Chairman Mark Rosenker pointed to a design error in the plates that helped connect the bridge's steel beams as a "critical factor."
The NTSB has also focused on the weight of construction materials that were on the bridge for a resurfacing project.