Deficiency (Structurally Deficient, SD, and Functionally Obsolete, FO) are defined in http://www.fhwa.dot.gov/legsregs/directives/fapg/0650dsup.htm (Note: Bridges with a Year Built or Year Reconstructed within the past 10 years will not be assigned a deficient status.)
All codes for all items in the National Bridge Inventory can be found in the Recording and Coding Guide for the Structure Inventory and Appraisal of the Nation's Bridges located at : http://www.fhwa.dot.gov/bridge/bripub.htm