My rural state of Iowa has more public road miles than the combined total interstate miles in all 50 states. Of our 24,242 bridges spanning at least 20 ft carrying highway traffic, 5025 are structurally deficient (20.7%). We are 1st in the nation in number and 3rd in percentage according to the Federal Highway Administration’s 2016 National Bridge Inventory. The data is presented by the American Road & Transportation Builders Association in Washington DC.
This photograph shows a public bridge at least 20 ft long which suffered complete failure for a variety of reasons including deterioration with age and an excessive load. The flaws of bridges can be hidden from view. They need qualified inspectors who know what engineering points to examine.
Photo courtesy of Audubon County Iowa
Structurally Deficient does not mean the bridge is in immediate danger of collapse. But, it does need attention. The quote below from the Iowa Department of Transportation explains the term. According to the IA DoT inspection manual page I-24, routine inspections are not to exceed intervals of 24 months. This federal standard may be less if bridge conditions and traffic warrant. It may also be extended to 48 months based on certain criteria.
The phrases “structurally deficient,” “functionally obsolete” and “sufficiency rating” are federal terms used to identify bridges eligible for funding assistance under the federal Highway Bridge Replacement and Rehabilitation Program. Structurally deficient refers to bridges needing significant maintenance attention, rehabilitation or replacement. Functionally obsolete refers to bridges with deck geometry (e.g., lane width, shoulder widths), load carrying capacity, vertical clearance or approach roadway alignment that no longer meet the criteria for the system of which the bridge is a part.
How I See It 