No margin on collapsed bridge

A preliminary report cites that there was essentially no safety (or engineering margin) for the Minneapolis bridge that collapsed. With most bridges, one expects that they can handle loads well above that for which they were designed. They cite that the bridge was essentially unstable, in that the failure of any one component would collapse the whole thing, much like the World Trade towers.

Being totally exhausted from the current Ottawa follies, I'm not in a caustic mood here. Is all American infrastructure like this? What will happen in an earthquake? I shudder to think.