In an event like that, I would expect a complete inspection of the piers and any other elements that may have been affected. If the bridge is damaged enough for this kind of collapse to be possible, we should be either closing it or limiting it to light traffic until repairs can be made. Stuff like this shouldn't be left to to chance, and the fact that it seems to be that way so frequently in the US should be terrifying, and entirely unacceptable. We should be demanding better infrastructure with budgets for maintenance baked in.