June 11 (Bloomberg) -- A safety escort ahead of the over-size truck that struck and collapsed a bridge over Interstate 5 north of Seattle last year was on the phone and didn’t radio a warning about the structure’s height, a U.S. report shows.
The woman at the wheel of the “pilot” car told investigators she was speaking on a mobile-phone call May 23, 2013, as the truck behind her hit a steal beam that sent the structure plummeting into the Skagit River, according to records released today by the National Transportation Safety Board.
“She was watching the accident truck cross the bridge in her rear-view and side mirrors and saw dust and the bridge collapse,” the NTSB said in a summary of an interview with the pilot-car driver.
The bridge failure severed the major transportation artery between Canada and the U.S. West Coast and sent three people into the river, causing minor injuries.
The NTSB released dozens of reports, interview transcripts, photos and other documents. The agency is planning to issue a cause for the accident later this year. The NTSB is looking at how the bridge height was marked, how previous bridge collisions were investigated by state authorities and the actions of the drivers involved, according to the records.
The bridge gave way about 7 p.m. after the impact fractured a steel support beam.
The structure was built using a now out-of-date design that is vulnerable to failure if only one of its steel support members is damaged. Current bridges are built with redundant structures so that damage to any individual component won’t cause a complete breakdown.
The driver of the truck that hit the bridge told investigators he had to swerve to the right, where the structure of the bridge was lower, to avoid another truck passing him, according to the NTSB.
The pilot car ahead of the truck was carrying a pole about the same height as the truck’s load so that it would serve as a warning in case the bridge was too low. The pilot-car driver said her pole never hit the bridge, so she didn’t warn the truck driver, according to the NTSB.
A temporary span was installed in June 2013 and a permanent repair was installed in September.
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