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"In 1987, the Interstate Highway bridge over Schoharie Creek in New York State collapsed during a flood. After this accident, the Federal Highway Administration required every State to identify highway bridges over water which are likely to have scour problems and to identify bridges where scour is severe. Knowledge of bridge sites where scour is a potential problem will enable the States to monitor and improve conditions at these bridges ahead of time-- before they become dangerous."

(From "Bridge Scour: What's it all about" by the U.S. Geological Survey in Massachusetts.)

I grew up in Minneapolis and spent most of my adult life there; I traveled over the 35W ("thirty-five double-yah" in my neighborhood's idiolect) bridge over the MIssissippi River twice a day on my way from my South Minneapolis apartment to the University of Minnesota where I both worked and studied. (I-35 splits in two through the Minneapolis-St. Paul metropolitan area -- there's also a 35E that goes mostly through St. Paul and its suburbs).

I listen to the news and hear my accent. I hear this family, the Engebretsens, on CNN saying "We're just trying to stay positive!" when their wife and mom is missing and think -- that's so like Minnesotans.

But I'm also obsessing a lot about what happened, structurally speaking, to that bridge.

The bridge crossed a particularly swift segment of the Mississippi, just south of the two dams and series of locks at St. Anthony Falls, where the river drops 49 feet (and just a mile-and-a-half north of the Washington Avenue Bridge, where poet John Berryman committed suicide in 1972). In some parts of the river you can swim in relative safety. Where the bridge crossed the river, you could not.

Despite what Minnesota's governor has been saying, it's not true that the bridge wasn't known to be structurally deficient. A 2005 report contained in the U.S. Department of Transportation's National Bridge Inventory database says that it was. The bridge was rated at 50 percent, meaning it was possibly in need of replacement.

And it's not the only one. In March of this year, the American Society of Civil Engineers recommended that a bridge safety program be "established, fully funded and consistently operated" to ensure "the operation of safe, reliable and efficient transportation system." The group reviews the country's infrastructure every two years and issues a "report card" for certain cities and categories. (Experts from the ASCE have been interviewed repeatedly about last month's pipeline explosion in Manhattan -- an accident that's of a piece with this one.)

In 2005, bridges got a "C." Twenty-seven percent of the nation's bridges are in the same condition.

Other states have other infrastructure woes (in California, it's the levees).

Metafilter has a great thread going on this, naturally, with some local insights. The Strib has a list of past bridge disasters, including the Schoharie Creek bridge mentioned above, where 10 people died.

But the theory I had when I began this post has been disproved. The 35W bridge over the Mississippi was not a victim of scour. As I learned from the Wikipedia page on the bridge, it "was notable for not having any piers in the water."

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