To give you an example of what can happen with aging infrastructure, on September 30, 2006 an overpass in Laval, Quebec, Canada collapsed killing 5 people. As you might expect this caused near panic in Quebec, perhaps similar to what happened recently in Minnesota. The Quebec Transport Department identified 135 bridges, overpasses and ramps that it targeted for special inspection because of concerns they could collapse. The Department was so seriously concerned that it imposed load restrictions on trucks traveling over these structures. Last Friday the Quebec Transport Department reported that its emergency inspection program has found that that 65 % of the 20 overpasses investigated so far under an emergency inspection program must either be replaced or undergo major repair and reinforcement. Apparently a number of serious problems have been discovered because many of these structures are old, and "after 40 years the concrete is not in good shape." The results of the emergency inspection program suggest that Quebec's inspection procedures have been "too superficial." Also it was suggested that repairing these structures will require "a very heavy budget commitment." Apparently it takes a week or more to check each overpass against the original plans, to sample the concrete and then analyze the data.
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