SAINT PAUL, Minn. - Thousands of vehicles continue to zip across the Lafayette Bridge daily in downtown Saint Paul. This despite the fact that the Minnesota Department of Transportation (Mn/DOT) regarded the bridge as more structurally deficient five years ago than the 35W bridge that collapsed.
However, the Lafayette Bridge, over the Mississippi River, is being replaced and soon. "It will be twin bridges, northbound and southbound," said Nancy Daubenberger, Mn/DOT State Bridge Engineer. The northbound span will be finished first, then carry all of the traffic while the old bridge is demolished and replaced by the new southbound span. All of the work is to be complete by 2015.
Daubenberger insisted that Minnesota motorists need not fear another 35W bridge collapse disaster. "Bridges in Minnesota are safe and, in fact, we are making a number of improvements in the way of bridge safety, along with the '152' program."
She was referring to the 2008 Trunk Highway Bridge Improvement Program, referred to as "Chapter 152" because of the section of Minnesota Laws where it is found. In the wake of the 35W collapse, the Legislature set aside $2.5 billion and identified 172 bridges in the state that needed to be replaced or rehabilitated by 2018.
Bridges are listed in three categories: "Structurally deficient", "Fracture Critical" and "Functionally Obsolete."
"But the one that Chapter 152 really focused on was the "structurally deficient" bridges, the ones that have deteriorated and put the public at risk," said State Representative Michael Beard, R-Shakopee, the House Transportation Committee Chair. "We are really focused on those bridges. We never want to see another 35W happen again."
"Structurally Deficient" means the state must lower its rating of the bridge, lower the speed (limit) or replace the bridge immediately.
"Fracture Critical" describes the design characteristics common to bridges in the 1950's and 60's, like the 35W bridge and the Lafayette Bridge. "It is basically two big beams with a bridge on top, but if any one of them (beams) breaks, the whole bridge falls down," said Beard. "It is important to understand that we have a lot of 'fracture critical' bridges that are actually very robust and doing their job, but we will replace those with a new design a quickly as we can."
"Functionally Obsolete" refers to how the bridge was intended to be used. "That is basically, your old culvert or steel bridge you see out in the country that was built for a ten ton tractor and now farmers are driving 20 ton tractors. So, it is obsolete, but it is because the use of the bridge has changed, not because the bridge has changed," said Beard.
Mn/DOT insists it has changed its way of doing things since 2007. Bridge designs now get a "formal independent peer review" and the agency has added 55 staffers for bridge maintenance a 50 percent increase.
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