"The driver of the oversize load reported to investigators that he felt 'crowded' by the passing combination vehicle so he moved his vehicle to the right," the NTSB said in a preliminary report released this week.
"As the oversize load was being transported across the bridge, the top of the load collided with the overhead portal and multiple sway braces on the far right side of the truss structure," the agency's report continued. "The impacts caused significant damage to load-bearing members of the bridge’s superstructure, resulting in the failure and subsequent collapse of the northernmost bridge span."
The NTSB said that the load the truck driver was carrying was 15 feet, 9 inches high, compared to a clearance at the lowest portion of the I-5 bridge, which was 14 feet, 8 inches high.
Despite the fact that the I-5 bridge collapse was caused by a truck accident, transportation advocates have seized upon the incident to argue for more spending on road and transit projects.
Rep. Rick Larsen (D-Wash.) said on the floor of the House on Tuesday that the bridge collapse showed Congress should appropriate more money for transportation projects because "we can’t keep waiting until [bridges] crumble into the water below."
"We know how to build safe bridges," Larsen said. "There are thousands of civil engineers devoting their lives today to building good structures that don’t fall down. But we need to pay for them. We need to maintain our bridges until they are old, and then we need to replace them."
The NTSB has said that it will release gradual updates as it continues its investigation of the Washington state accident.