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Accident Report Detail

Collapse of the Interstate 5 Skagit River Bridge Following a Strike by an Oversize Combination Vehicle

Executive Summary

‚ÄčOn Thursday, May 23, 2013, about 7:05 p.m. Pacific daylight time, a 2010 Kenworth truck-tractor in combination with a 1997 Aspen flatbed semitrailer hauling an oversize load (referred to here as "the oversize combination vehicle") was traveling south on Interstate 5 (I-5) near Mount Vernon, Washington. The oversize combination vehicle had a permit for the route of travel and was being led by a pilot/escort vehicle, a 1997 Dodge Ram pickup truck. As the oversize combination vehicle traveled across the I-5 bridge above the Skagit River, the oversize load struck the bridge, damaging its structure. The oversize combination vehicle continued to travel across the bridge and came to a stop on I-5 south of the bridge.

As a result of contact damage to the bridge's truss structure, span 8 of the 12-span bridge collapsed into the Skagit River. Two passenger vehicles, a southbound 2010 Dodge Ram pickup truck towing a Jayco travel-trailer and a northbound 2013 Subaru XV Crosstrek, fell into the river. Two other vehicles were damaged during the event: a 2000 Kenworth truck-tractor in combination with a 1996 refrigerated semitrailer in the southbound passing lane made contact with the oversize combination vehicle, and a southbound 1995 BMW 525i received undercarriage damage. Eight vehicle occupants were involved in the bridge span collapse; three received minor injuries and five were uninjured.

Probable Cause

‚ÄčThe National Transportation Safety Board determines that the probable cause of the Interstate 5 Skagit River Bridge span collapse was a strike to the bridge structure by an oversize combination vehicle that failed to travel in a lane with adequate overhead clearance due to deficiencies in the interdependent system of safeguards for oversize load movements. These deficiencies included (1) insufficient route planning by Mullen Trucking LP and the oversize combination vehicle driver; (2) failure of the certified pilot/escort vehicle driver to perform required duties and to communicate potential hazards, due in part to distraction caused by cell phone use; and (3) inadequate evaluation of oversize load permit requests and no provision of low-clearance warning signs in advance of the bridge by the Washington State Department of Transportation.

Accident Location: Mount Vernon , WA USA Interstate 5 Skagit River Bridge
Accident Date: 5/23/2013
Accident ID: HWY13MH012

Date Adopted: 7/15/2014
NTSB Number: HAR1401
NTIS Number: PB2014-106399