Structurally Deficient

What It Means

A bridge is classified as structurally deficient under current FHWA criteria when any of its primary load-carrying components, deck (NBI Item 58), superstructure (Item 59), substructure (Item 60), or culvert (Item 62), receives an NBI condition rating of 4 (Poor) or lower on the 0-9 scale. This definition was formalized in 2018 when FHWA retired the older "Structurally Deficient or Functionally Obsolete" combined metric in favor of the three-tier Good/Fair/Poor framework required under MAP-21 performance measures. Being structurally deficient does not mean a bridge is unsafe or at imminent risk of collapse, it means the bridge has significant deterioration requiring substantial maintenance, rehabilitation, or replacement to restore it to acceptable condition. Structurally deficient bridges remain open to traffic (unless a separate engineering evaluation determines closure is warranted) but are inspected more frequently than the standard 24-month cycle, sometimes annually or quarterly depending on the severity of the rating and rate of deterioration. As of the most recent NBI release, approximately 46,000 of the nation's 617,000+ bridges (roughly 7.5%) are classified as structurally deficient, with concentrations in Iowa, Pennsylvania, West Virginia, Oklahoma, and Louisiana. The I-35W Mississippi River bridge collapse in Minneapolis in August 2007, which killed 13 people, was rated structurally deficient at the time of failure, driving a major overhaul of federal inspection protocols including stricter gusset plate evaluation requirements. More recently, the Fern Hollow bridge collapse in Pittsburgh in January 2022 (rated Poor for years before collapse) and the Francis Scott Key Bridge collapse in Baltimore in March 2024 (though caused by container ship strike rather than deterioration) renewed public attention to the backlog of deficient structures and accelerated IIJA bridge funding disbursement to states and localities.

Frequently Asked Questions