The Bridges are Alright

"The scary-sounding phrases structurally deficient and functionally obsolete combined with those big numbers are enough to make you bite your nails bloody every time you drive over a river or beneath an underpass. Yet if any of the cited pieces paused to define either inspection term, you'd come away from the alarmist stories with a yawn. As a 2006 report by U.S. Department of Transportation's Federal Highway Administration puts it (very large PDF):

Structural deficiencies are characterized by deteriorated conditions of significant bridge elements and reduced load carrying capacity. Functional obsolescence is a function of the geometrics of the bridge not meeting current design standards. Neither type of deficiency indicates that the bridge is unsafe.

A 'structurally deficient' bridge can safely stay in service if weight limitations are posted and observed and the bridge is monitored, inspected, and maintained. A bridge designed in the 1930s could be deemed "functionally obsolete" because it's narrower than modern standards dictate or because its clearance over a highway isn't up to modern snuff, not because it's in danger of tumbling down. (The Department of Transportation's 2004 inventory found 77,796 U.S. bridges structurally deficient and 80,632 functionally obsolete, for a totally of 158,428 deficient bridges.)"