If you can believe the Weather Channel aired last night a one hour documentary on that collapse. It was blamed on construction at the time. And a delivery of materials piled in one vulnerable part of the structure, where the gussets plates were 1/2 the design thickness. Also of note were the lack of movement in rollers designed to carry freezing shifts in the structure.
Lots of issues. Throw in the added weight and vibration from the contractor on the bridge deck and you got a recipe fof disaster.