Structurally Deficient

The Federal Highway Administration has established definition for Structurally Deficient. Structural deficiency ratings are based on the National Bridge Inventory ratings scale.

Structurally Deficient (SD) Status - A highway bridge is classified as structurally deficient if the deck, superstructure, substructure, or culvert is rated in "poor" condition (0 to 4 on the NBI rating scale). A bridge can also be classified as structurally deficient if its load carrying capacity is significantly below current design standards or if a waterway below frequently overtops the bridge during floods.