A brief assessment issued by the National Transportation Safety Board said the oversize load collided with the far right side of the truss structure on the evening of May 23, resulting in the collapse of the bridge into the Skagit River. The driver reported that his load was 15 feet, 9 inches tall while the lowest portion of the bridge braces was just 14 feet, 8 inches.
The NTSB has been looking to speak with the driver of the truck and trailer that passed the oversize load, but board spokesman Peter Knudson said officials still have not found the person or vehicle.
"We want to find out what the driver's perspective was," Knudson said.
Both trucks made it across the bridge, escaping the collapse, but two other vehicles fell into the water and three people were rescued with mostly minor injuries.
Traffic on the interstate has been detoured since the collapse, causing congestion and delays. As the main highway between Seattle and Vancouver, British Columbia, that section of corridor typically carries 71,000 vehicles a day. Washington State Patrol Trooper Sean O'Connell was killed while directing detoured traffic in Conway on May 31 when his motorcycle collided with a truck.
Crews are now working to put in place a temporary span, hoping to have the roadway operational again next week.
A final report on the cause of the accident is still months away, but Tuesday's filing laid out many of the facts known to investigators. The operator of the pilot vehicle told investigators that the clearance pole mounted on the front of her vehicle was set at 16 feet, 2 inches high - leaving room between the top of the pole and the top of the load.