By David Tanner, associate editor
It all happened in a matter of seconds, but the fallout from the Interstate 5 bridge that collapsed in Washington state in May will live on for months, even years.
Federal investigators had their work cut out for them when they arrived to find a 160-foot section of the Skagit River Bridge resting in a crumpled heap in the riverbed. Just a few hours had passed since a southbound truck carrying an oversized load struck overhead supports and sealed the bridge’s fate in the early evening of May 23.
Early press briefings by the National Transportation Safety Board showed the agency was focusing on the bridge itself and the load that struck it.
NTSB Chairman Deborah Hersman revealed that the bridge had been struck numerous times by trucks in the past, most recently in October 2012.
Investigators pored over bridge history and scrutinized the permit issued to Canadian company Mullen Trucking and driver William Scott who was transporting the load. They interviewed the pilot car driver and even traveled to Alberta to comb through company records.
But it wasn’t until 12 days after the collapse that investigators widened their lens and began looking at the bigger picture: that a second truck had been passing, or attempting to pass, the oversized load, “pinning” it over to the right where it had no chance to clear the overhead bridge supports.
On June 5, the Washington State Highway Patrol issued a bulletin searching for the second tractor trailer. But even with video evidence, they didn’t have much to go on except that it was an unknown color semi pulling a white trailer.
Six days after that, on June 11, the NTSB acknowledged the second truck in a preliminary report released to the public. The report narrated what an eyewitness in a passenger vehicle – who was one of three occupants of passenger vehicles rescued from the river after falling with the bridge section – told investigators and local news in Seattle.
“According to witnesses, as both vehicles approached the bridge, another southbound truck-tractor in combination with a semitrailer overtook and passed the oversize load in the left lane,” the NTSB stated in its report.
“The driver of the oversize load reported to investigators that he felt ‘crowded’ by the passing combination vehicle so he moved his vehicle to the right. As the oversize load was being transported across the bridge, the top of the load collided with the overhead portal and multiple sway braces on the far right side of the truss structure. The impacts caused significant damage to load-bearing members of the bridge’s superstructure, resulting in the failure and subsequent collapse of the northernmost bridge span.”
The over-height permit obtained by Mullen Trucking was for 15 feet, 9 inches. According to the NTSB, the overhead clearance on the Skagit River Bridge was 18 feet high down the center but just 14 feet, 6 inches at the right edge of the right lane. Investigators said the pilot car ahead of Scott’s vehicle had a clearance pole measured at 16 feet, 2 inches.
The NTSB has not released an exact cause of the bridge collapse beyond the narrative of events and witness testimony. The agency will issue a final report in a few months.
Meanwhile, congressional committees have called hearings to discuss aging infrastructure and a deficient Highway Trust Fund.
Sen. Patty Murray, D-Wash., who chairs the Senate Appropriations Subcommittee on Transportation, Housing and Urban Affairs, said the U.S. can expect the worst if Congress does not address the problem.
“Unfortunately, this is the kind of disaster we can expect to happen more often when our roads and bridges fall into disrepair,” Murray stated during the hearing, which featured Federal Highway Administrator Victor Mendez as well as the U.S. DOT undersecretary for policy, Polly Trottenberg, and a Government Accountability Office official, Phillip Herr.
“Roads are going to need to be fixed eventually, bridges will need to be strengthened before they collapse, and waiting will only make the work more expensive and more difficult when we eventually do it,” Murray said. LL