02-August-2007, 07:55 PM
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Established Member
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Join Date: Mar 2002
Location: Concord, NC
Posts: 1,585
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From NPR
Quote:
• According to the Federal Highway Administration, in 2004 there were 594,101 bridges over 6.1 meters (20 feet) long in the United States.
• About 56,000 of these bridges are on interstate highways — including the Interstate 35 bridge that collapsed in Minnesota.
• Although roughly three-quarters of the nation's bridges are in rural areas, urban bridges carry roughly three-quarters of the nation's traffic.
• U.S. highway bridges are, on average, 40 years old. The typical interstate bridge was built in the late 1960s (the I-35 bridge was finished in 1967).
• Most bridges are inspected and rated every two years. Engineers rate bridges that that are deteriorating or don't meet current highway design or engineering standards as "structurally deficient" or "functionally obsolete." Neither designation necessarily means that a bridge is unsafe. For instance, a bridge can be judged deficient if it has shoulders that are too narrow or was built with outmoded construction techniques.
• In 2005, engineers rated the I-35 bridge in Minnesota as "structurally deficient" and possibly in need of replacement.
• Overall, about 20 percent of interstate bridges (nearly 12,000 bridges) were rated as deficient in one way or another in 2004. The percentage of deficient bridges has been dropping over the last decade.
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and
Quote:
The White House on Thursday said an inspection two years ago found problems in the 40-year-old bridge. Spokesman Tony Snow said the structure — which was under repair at the time of the collapse — rated only 50 on a scale of 120 for structural stability, but he added that that "doesn't mean there was a risk of failure."
Echoing Snow's remarks during a news conference in Minnesota, Secretary of Transportation Mary Peters said the ratings did not indicate there was any danger, just that the bridge should be scheduled for rehabilitation.
"What that rating of 50 means is that the bridge should be repaired, should perhaps be considered for replacement at some point in the future," Peters said. "It was by no means determined that this bridge was not safe. Had that been the case … Gov. Pawlenty would have shut this bridge down immediately."
The federal government
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