Federal board investigating bridge collapse
The chairwoman of the National Transportation Safety Board said Saturday that the bridge collapse in Washington state is a wake-up call for the U.S. “This is a really significant event and we need to learn from it, not just in Washington but around the country,” Debbie Hersman said after taking a boat ride on the Skagit River below the dramatic scene where a truck bumped against the steel framework, collapsing the bridge and sending two vehicles and three people into the chilly water.
Her team will spend a week to 10 days looking at the bridge, talking to the truck driver whose vehicle hit it, and examining maintenance documents and previous accident reports They’ll be looking for safety issues that could affect other bridges. “The results can be very catastrophic,” Hersman said. “We’re very fortunate in this situation.”
Associated Press
Thousands of bridges around the U.S. may be one freak accident or mistake away from collapse, even if the spans are deemed structurally sound.
The crossings are kept standing by engineering design, not supported with brute strength or redundant protections like their more modern counterparts. Bridge regulators call the more risky spans “fracture critical,” meaning that if a single, vital component of the bridge is compromised, it can crumple.
Those vulnerable crossings — which carry millions of drivers every day — include the I-5 bridge over the Skagit River north of Seattle, which collapsed late Thursday after an oversized truck load clipped its steel truss.
Public officials have focused in recent years on the desperate need for money to repair thousands of bridges deemed structurally deficient, which typically means a major portion of the bridge is in poor condition or worse. But the bridge that collapsed last week is not in that category, despite its “fracture critical” rating, highlighting another major problem with the nation’s infrastructure: Although it’s rare, some bridges deemed to be fine structurally can still be crippled if they are struck hard enough in the wrong spot.
The most famous failure of a fracture critical bridge was the collapse of the I-35W bridge in Minneapolis during rush hour on Aug. 1, 2007, killing 13 people and injuring more than 100 others. The National Transportation Safety Board concluded that the cause of the collapse was an error by the bridge’s designers, who made a gusset plate, a key component of the bridge, too thin.
Because the bridge’s key structures lacked back-up supports, when the gusset plate broke, much of the bridge collapsed.
Such bridges are the result of Congress trying to cut corners to save money, said Barry B. LePatner, a New York real estate attorney and author of “Too Big to Fall: America’s Failing Infrastructure and the Way Forward.”
About 18,000 fracture critical bridges were built from the mid-1950s through the late 1970s in an effort to complete the nation’s interstate highway system, LePatner said. The fracture critical bridge designs were cheaper than bridges designed with extra supports, he said.
“They have been left hanging with little maintenance for four decades now,” he said. “There is little political will and less political leadership to commit the tens of billions of dollars needed” to fix them.
There has been little focus or urgency in replacing the older fracture critical crossings, in part because there is a massive backlog of bridge repair work for thousands of bridges deemed to be structurally problematic. Hundreds of bridges in Washington state and around the coutnry have worse ratings than the one that collapsed.
Along with being at risk of a fatal impact, the I-5 bridge was deemed to be “functionally obsolete,” which essentially means it wasn’t built to today’s standards. Its shoulders were narrow, and it had low clearance.
There are 66,749 structurally deficient bridges and 84,748 functionally obsolete bridges in the U.S., including Puerto Rico, according to the Federal Highway Administration. That’s about a quarter of the 607,000 total bridges nationally. States and cities have been whittling down that backlog, but slowly. In 2002, about 30 percent of bridges fell into one of those two categories.
Spending by states and local government on bridge construction adjusted for inflation has more than doubled since 1998, to $28.5 billion last year from $12.3 billion, according to the American Road and Transportation Builders Association. That’s an all-time high.
“The needs are so great that even with the growth we’ve had in the investment level, it’s barely moving the needle in terms of moving bridges off these lists,” said Alison Premo Black, the association’s chief economist.
There is wide recognition at all levels of government that the failure to address aging infrastructure will likely undermine safety and hinder economic growth. But there is no consensus on how to pay for improvements. The federal Highway Trust Fund, which provides construction aid to states, is forecast to go broke next year. The fund gets its revenue primarily from federal gas and diesel taxes. But revenues aren’t keeping up because people are driving less and there are more fuel-efficient cars on the road.
Many transportation thinkers believe a shift to taxes based on miles traveled by a vehicle is inevitable, but there are privacy concerns and other difficulties that would preclude widespread use of such a system for at least a decade.
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