Monday, February 9, 2015

America's Crumbling Infrastructure: Bridge Edition


Structural deficiency sounds scary, and it is, sort of. Deficient bridges are, broadly speaking, safe to drive across. In an interview last year with CBS, former Transportation Secretary Ray LaHood said that structurally deficient bridges "need to be really either replaced or repaired in a very dramatic way." He went on: "I don't want to say they're unsafe. But they're dangerous."
Not unsafe, but dangerous: that's the paradox of structural deficiency in a nutshell. When bridge engineers evaluate a bridge, they grade the condition of each of its major components -- its supports, the deck that vehicles travel across, etc. -- on a 0 to 9 scale. If any of these components receive a grade below a given threshold, the bridge is deemed structurally deficient. It needs some repair work to get back up to snuff.
Looking at the map above, it's immediately clear that some states have a bigger structural deficiency problem than others. Twenty two percent of Pennsylvania's 23,000 highway bridges are deficient, which, if you've ever had the misfortune of driving up I-81 in that state, you know in your heart to be true. Twenty one percent of Iowa's bridges don't make the grade. Same goes for 20 percent of South Dakota's, and 18 percent of Oklahoma's. These percentages are all considerably higher than the nationwide average of about 10 percent.
On the other hand, Nevada is doing the best job of keeping its bridges up to code -- fewer than 2 percent of that state's bridges are deficient. Likewise only 2 percent of Florida and Texas bridges are deemed deficient, and 3 percent of Arizona and Utah's.
There's another measure of bridge quality that the FHA tracks, and that's "functional obsolescence." This sounds even scarier than structural deficiency, but is in many respects more benign. It simply means that a bridge was built to specifications that no longer meet modern requirements. It may be too narrow, or too light, or unable to deal with the heavier weights of today's vehicles. Obsolete bridges don't necessarily need to be repaired, but they do need to be replaced -- nobody wants to drive an 18-wheeler across a span built to accommodate Model Ts.

The geography of bridge obsolescence is distinct from the geography of deficiency. Obsolete bridges are strongly clustered in the Northeast, which makes sense: older cities = older bridges. More than a quarter of New York's bridges are obsolete, as are a third of Rhode Island's, 43 percent of Massachusetts', and a whopping 65 percent of DC's. Nationally, only about 14 percent of bridges are obsolete.
So you can start to see what's at stake when we talk about our bridge infrastructure. Overall, about one quarter of our nation's bridges are either obsolete or deficient. This means that roughly 1 out of every 4 bridges you drive over is in need of work done. The American Society of Civil Engineers -- who, let's face it, have a vested financial interest in making this work happen -- estimates that it would take a $20.5 billion annual investment to eliminate our deficient bridge backlog by 2028.
I seriously doubt that the states are all rating their bridges in the same way (which the post does discuss).  Personally, I believe we will never be able to maintain all the constructed infrastructure currently in place, and we continue adding new infrastructure as our metropolitan areas sprawl out.  Even worse, that new infrastructure serves a much less dense population than the existing infrastructure.  We are going to face some extremely challenging funding problems in the near future.  I'm sure rural areas will suffer when the decisions are made for which problems get fixed.

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