It's been one year since a truck with an oversized load struck a beam on the I-5 bridge over the Skagit River, sending a section plunging into the water below. But very little has changed to prevent another similar accident from happening again on any number of bridges across the state.
Investigators determined the oversize load struck several overhead support beams on the bridge, leading to the collapse. The bridge, build in 1955, was considered "functionally obsolete" because it did not meet current design standards for lane widths and vertical clearance.
"The state still hasn't fixed the underlying issue that caused the bridge collapse, which is trucks that are too big for those bridges have been allowed and permitted," says state Sen. Mike Baumgartner, R-Spokane.
Baumgartner proposed a bill following the collapse that would have forbid the Washington State Department of Transportation from issuing an over-height or over-width special permit for vehicles moving a load that exceeds the actual measured minimum clearance height or width of a bridge along a vehicle's proposed route. The measure, which failed to pass, would have required proper signage for all structures that provide less than 16 feet of clearance above public highways.
The Skagit River bridge was one of many built in the 1950's with greater clearance in the middle than the sides, says Charles Roeder, a professor of civil engineering at the University of Washington. "That's the problem," he says. "It just wasn't made to handle modern loads and traffic."
The bridge had a clearance of around 17 feet above the inside lane, but just 14 feet 7 inches on the outer lane, where the truck struck one of the tresses. Engineers replaced the collapsed span with a concrete structure and raised the remaining steel trusses to 18 feet.
While it was deemed structurally sound, the bridge's design was considered "fracture critical," meaning damage to a single overhead tress was enough to bring the entire span down. Roeder says the design is common for bridges built in the 1950's, and the state has many of the steel through-truss structures that pose similar risks.
Washington Secretary of Transportation Lynn Peterson says the state has been working with the trucking industry to improve information about bridges to help keep oversized loads from vulnerable bridges. But she says Baumgartner's proposal wouldn't prevent a truck driver who ignores the information from driving an oversized load into a potentially risky crossing.
"Regulation will not stop bad behavior," she says. "We can provide the permits with very specific directions of what roads to use and what roads not to use. Regulation would not have stopped the incident at Skagit from occurring."
Although the Skagit River Bridge was considered structurally sound, WSDOT lists 139 other state-owned bridges as structurally deficient. Bridges with that designation require repair or replacement of a certain component or the entire bridge.
Roeder and the state both say it doesn't mean any of the structures face imminent risk of collapse or pose a danger to drivers. But the civil engineering professor says it speaks to a growing decline in our infrastructure which will lead to more numerous and costly problems in the future.
"The allocation of our resources is such that we are neglecting our infrastructure," he says of the lack of funding for infrastructure maintenance and repair. "If we put more effort into this, probably we would need to have fewer replacements because we would be doing continual maintenance, we would be doing continual upgrading of our systems."
But Peterson says the money simply isn't there to fix everything.
"We're going to have to prioritize which assets get maintained maybe a little differently than we have in the past," she says.
Peterson says the state is continually monitoring the condition of bridges and is doing all it can to stretch out their useful lives as long as possible, including restricting the size and weight of loads if experts determine they are increasing the rate of deterioration.
"What we know right now is that without additional funding we will have 71 more structurally deficient bridges that could be load limited than if we had gotten funded," she says.
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