A comment from someone on the Internet...

"The posting today on the Minneapolis Bridge collapse doesn't make sense. How can gusset plates 1/2 the proper thickness and designed for a factor of safety of 1.3 not collapse before now. The bridge or "dead weight" is always the same and the "live rolling loads" (cars and trucks) can't weigh any more than a traffic jam that has the cars lined up bumper to bumper on the bridge. Surely if the gusset plates were under sized by a factor of 2 there would have been a failure before now. I am a Structural Engineer that's how I know something is up with the official explanation."