On July 15, 2014 The National Transportation Safety Board, or "NTSB," met to discuss their investigation into the May 23, 2013 collapse of the Skagit River Bridge in Mt. Vernon, Washington, detailing their rationale for the conclusions, probable cause, and safety recommendations.
Cause of The Skagit River Bridge Collapse
The NTSB has determined that the the Washington State Department of Transportion, Mullen Trucking, and the escort driver share the blame for the collapse of the Skagit River Bridge on May 23, 2013. According to the executive summary of the NTSB's final investigation report, probable cause of the Interstate 5 Skagit River Bridge span collapse was a strike to the bridge structure by an oversize semi truck. Multiple deficiencies in the interdependent system of safeguards for movements of oversize loads in Washington State, but these can be summarized as:
- Insufficient route planning by Mullen Trucking LP and the truck driver vehicle driver.
- Failure of the escort vehicle driver to perform required duties and to communicate potential hazards.
- Washington State Department of Transportation's inadequate evaluation of oversize load permit requests and lack of low-clearance warning signs on approach to the bridge.