According to a National Transportation Safety Board report, engineers determined a tractor-trailer carrying an oversize load struck the truss over the southbound lanes on the north side of the bridge, causing part of the span to fail and fall into the river.
The driver of the semi was cited in the report, saying he moved to the right lanes before hitting the span because he felt “crowded” out by another semi passing in the left lanes.
The move put the truck’s load, listed in the report as a casing shed, in line with one of the lowest parts of the span.
NTSB investigators interviewed the driver of the pilot car who stated that the pole on the front of her vehicle was 16 feet 2 inches tall, 5 inches taller than the trailing semi’s load height. The bridge’s clearance in the center lane, where drivers with oversize loads are supposed to travel, was about 17 feet. In the far right lane, where the truss is lower, the clearance was 14 feet 8 inches.
According to the NTSB, the bridge’s overhead portal and sway braces suffered significant damage, weakening the northernmost span of the bridge to the point of collapse.
Two vehicles fell with the span into the river. A total of three people had to be rescued from the water.
Further inspection of the bridge in the days after the collapse revealed impact damage in an adjacent span.
The state has estimated the repairs to top $15 million.
Workers are nearing completion on a temporary span that could be finished by as early as next week.