Bridge safety

What happens when a component fails on a bridge? What if the design of the bridge makes a single failure more likely to bring the entire structure down?

These questions could be asked after the collapse of a bridge on the Interstate-5 freeway in the State of Washington.

Jim Miller (who writes extensively about National politics, and somewhat about local politics) notes that regional authorities had a process for testing and licensing for carrying oversized loads across bridges.

He also links to an article which has a very useful diagram about the bridge failure.

I've copied the image below.

Interestingly, it also appears that the inside lanes had more clearance than the outside lanes. That may have contributed to the loss, also...