NTSB investigation of I-5 bridge collapse continues

By Greg Grisolano, Land Line staff writer | 5/29/2013

Federal investigators reviewing the collapse of the Skagit River Bridge on Interstate 5 in Washington state are continuing their investigation of the bridge collapse.

A 160-foot span of the four-lane bridge fell into the waters of the Skagit River in Mount Vernon on May 23. Witnesses had reported that just prior to the collapse, an oversized tractor-trailer traveling southbound on I-5 struck the overhead truss superstructure.

The collapse occurred seconds after an over-height load guided by a pilot car struck bridge supports. The trucking company, Mullen Trucking of Aldersyde, Alberta, Canada, had a legal permit to haul the load on a designated route that included the I-5 bridge. The truck was piloted by William D. Scott, age 41, of Spruce Grove, Alberta.

A spokesman for the National Transportation Safety Board said the agency is currently interviewing the pilot car driver and conducting field inspections of spans of the bridge that plunged into the water.

“We don’t have any more information at this time,” said Terry Williams, NTSB spokesman. “It’s still an ongoing investigation.”

NTSB investigators have been on the scene since the night the bridge collapsed and are continuing to coordinate activities with the Washington Department of Transportation.

Two vehicles and a camper trailer that plunged into river when the bridge collapsed have been removed from the water, according to a news release issued by the agency. The release states that investigators hope to gain impact forces data from the air bag modules on each of the vehicles.

Williams said the NTSB was still in the process of verifying the measurements of the accident truck and trailer and load. In addition, a mechanical inspection of the accident truck found one flaw that would have put the truck out of service, but did not contribute to the accident.

The release also states that investigators are reviewing surveillance tapes of the accident sequence and additional eyewitnesses.

The Skagit River Bridge has a history of being struck by over-dimensional vehicles, NTSB Chairman Deborah Hersman said in a video conference yesterday.

The 60-year-old Skagit River Bridge carried 71,000 vehicles, including 6,500 commercial trucks, per day prior to a section collapsing on Thursday.

Hersman said inspection reports show an over-height vehicle struck the bridge as recently as Oct. 22, 2012.

“You can see with the naked eye visible damage and deformed metal in the first frame and in subsequent frames along the bridge – and again, this is from the last hit, last year,” Hersman said. “As you walk the bridge, you can see visible damage on other spans that is not so recent,” she continued. “Our team is obtaining inspection records going back further, and we will continue to look into the history of the bridge.”

The overhead bridge supports were 18 feet above the bridge deck toward the center of the two-lane southbound span, but arched down to a 14-foot, 6-inch overhead clearance at the narrow right shoulder.

The truck load was permitted at 15-foot 6-inches, giving it clearance toward the middle of the double lane but not enough clearance at the right shoulder.

A driver of one of two passenger vehicles that plunged into the Skagit River told KIRO 7 in Seattle that another semi “pinned” the oversized load in the right lane as the vehicles arrived at the bridge.

NTSB hopes to have a preliminary report in 30 days, but a final report could take months.

The U.S. Department of Transportation announced $1 million in emergency funds to help Washington State build a temporary span while waiting on a permanent replacement.

Washington Gov. Jay Inslee said a temporary span could be up and running in June and a permanent replacement built by September.

Land Line Associate Editor David Tanner contributed to this report.

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