There are many answers, but they all boil down to the structure of federal transportation funding.

Late last month, part of the Interstate 5 bridge in Washington state fell into the Skagit River. The bridge connects a key commercial corridor between Seattle and Vancouver, and while the immediate cause of the collapse was an oversized truck destabilizing the bridge, the structure itself had documented problems. It was classified as "functionally obsolete," meaning its design no longer met new traffic patterns, and it had a "sufficiency rating" of 46 out of 100, qualifying it for replacement.

No one died in the accident, amazingly and fortunately enough, but the entire situation tempted fate.

The same can sadly be said of any number of bridges in the United States that remain in dangerously bad shape. Of roughly 600,000 bridges across the country, a full quarter of them are officially categorized as problematic — meaning they're either "functionally obsolete," like the I-5, or "structurally deficient," with at least one component in poor condition. That doesn't always mean they're unsafe, but neither does it mean they're perfectly sound, and the amount of money needed to change that is estimated in the hundreds of billions of dollars.

What makes the situation so frustrating is that federal and state officials have known about these conditions for years. The current deficiency categories were created after the Silver Bridge over the Ohio River collapsed in the 1960s, killing dozens, but the problems still lingered. In 2008 — following another tragic collapse, the I-35 bridge in Minneapolis — the Government Accountability Office issued a report recommending that the country's bridge safety program get a pretty thorough overhaul.

That GAO report slammed the federal bridge program for lacking "focus" and clear goals. When GAO surveyed various state DOTs, for instance, it found that although federal bridge money was supposed to help reduce the inventory of deficient structures, not all states used it that way. Some states argued that the deficiency categories didn't indicate safety risk (in which case, what's the point of them?). Others said that funding formulas actually created a disincentive to fix bridges because fewer bad bridges could make a state eligible for less money.

Beyond that, states even had the option to transfer half of their allotted bridge money to general highway projects.

Last week, in the aftermath of the I-5 collapse, GAO revisited its recommendations in testimony before several Senate subcommittees. This new report offered some encouraging signs. For one thing, the latest highway funding reauthorization (known as MAP-21) did create clearer bridge goals: performance measures, mandatory state progress reports, and requirements for corrective action among them. GAO also noted that in the past ten years the total number of deficient bridges has actually decreased by 23,000.

But even these positive steps are tempered by new concerns. For all the efforts of MAP-21 guidelines, the DOT still struggles to measure impact on federal bridge investment, because it doesn't track figures on state and local bridge spending. (Seems like a great place for Big Data to step in, no?) And while total bridge deficiencies are dropping, total bridges are rising, meaning many states are neglecting the type of fix-it-first transportation mantra that most experts (and President Obama) recommend.

In other words, why is America building so many new bridges when its old ones remain in crummy shape?

The core problem still boils down to transportation funding. Just before the I-5 bridge fell, the Seattle section of the American Society of Civil Engineers estimated that Washington state had a $28.1 billion backlog of bridge replacements and repairs [PDF]. Back in 2008, state officials told the GAO they faced an especially tricky situation with bridges in urban corridors: funding just one of these mega-projects could mean ignoring all other state bridges for years.

These days there are ad hoc ways to fix bridges, such as public-private infrastructure partnerships, though those efforts can create new problems of their own. In the end, though, this problem isn't likely to change until (both state and federal) lawmakers admit that the traditional model of transportation funding (via the gas tax) is broken and embrace alternative ones (such as mileage fees). Sometimes it's hard to see the consequences of political inaction, but sometimes they wash up as rubble on the banks of a river.

Charts via GAO. Top image: the May 24 Skagit River bridge collapse. (REUTERS/Cliff DesPeaux)

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