WASHINGTON - The collapse of an interstate highway bridge in Washington brings renewed attention to the limits of the country's infrastructure, especially older structures that were designed with little room for error.
The Interstate 5 bridge over the Skagit River in Mount Vernon, Wash., was considered outdated but not structurally deficient. While state police believe an oversize truck hitting the bridge may have contributed to its collapse, an investigation by the National Transportation Safety Board will ultimately pinpoint the cause.
Authorities are trying to find a temporary span for the Skagit, although it won't come in time for the tens of thousands of Memorial Day vacationers who would travel between Canada and Seattle.
"You cannot overstate the importance of this corridor to Washington state," Gov. Jay Inslee said. Traffic on I-5 and surrounding roads was backed up for miles Thursday night and Friday, a situation the governor said would continue indefinitely.
Officials were looking for a temporary, pre-fabricated bridge to replace the 160-foot section that failed, Inslee said Friday. If one is found, it could be in place in weeks. If not, it could be months before a replacement can be built, the governor said.
Experts said the I-5 bridge shares a design feature with thousands of other bridges across the country that make them more vulnerable to failure. It was fracture-critical, which means there is no redundancy in the structure - if one component fails, the whole bridge can collapse. It's a scenario that's happened before, and experts say it will happen again if older, obsolete bridges are not replaced or reinforced.
"This is a repetitive story that's going to play out again like a horrible nightmare," said Barry LePatner, a New York construction lawyer who's identified nearly 8,000 of the country's most troublesome spans.
A 40-year-old interstate bridge in Minneapolis that collapsed into the Mississippi River in 2007 also had a fracture-critical design. Thirteen people were killed and scores more were injured. No one was killed or seriously injured in Thursday's collapse.
"It could have been a lot worse," said Pat Natale, executive director of the American Society of Civil Engineers.
Another fracture-critical bridge over the Ohio River between Louisville, Ky., and New Albany, Ind., was closed for several months in 2011 after inspectors discovered a large hidden crack that could have proved disastrous. Engineers added reinforcement to the structure for a fraction of the cost of replacement, and LePatner said that a bridge like the one on I-5 similarly could have been made stronger.
"Government officials have failed to fund needed maintenance, and these bridges have long passed their intended lifespan," he said.
The oldest parts of the Interstate Highway System are more than 50 years old and need repair and replacement just as states and the federal government confront shrinking funds to build and maintain infrastructure.
At a news conference Friday, Washington Secretary of Transportation Lynn Peterson said that only the section of the bridge that collapsed would be rebuilt. Washington Gov. Jay Inslee said the repair would cost $15 million - a replacement could cost many times more.
Washington state has much incentive to finish the repairs quickly. I-5 is the primary highway corridor along the Pacific Coast, carrying an average of 71,000 vehicles including 10,000 trucks a day, which will have to endure lengthy and costly detours until the bridge is repaired.