Poor maintenance is a difficult problem to diagnose in the wake of a bridge collapse. Many bridge collapses could have been prevented with more stringent inspection and maintenance routines, and lots of collapses that occur for other reasons are exacerbated by poor maintenance. When a bridge is designed, the engineers assume a certain level of maintenance that is necessary for the bridge to live out its intended lifespan. Rusted parts must be replaced, drainage areas cleared, new coats of paint applied and reinforcements added if traffic levels have increased.
A bridge carrying the Connecticut Turnpike over the Mianus River collapsed in the middle of the night in June 1983. The collapse was due to the failure of steel pins that had corroded. Investigators ruled that the bridge's design and construction weren't at fault -- the collapse was blamed on deferred maintenance that would have spotted and replaced the rusted pins [source: NYCRoads].