The inventory is developed for the purpose of having a unified database for bridges to ensure the safety of the traveling public, as required by the Federal Aid Highway Act of 1968.
Furthermore, the bridge inventory contains information regarding to inspection data, ratings assigned by inspectors, and appraisal results.
The term "functionally obsolete" has been removed from published NBI data, as it is no longer tracked.
"[4] In December 2008, 72,868 bridges in the United States (12.1%) were categorized as "structurally deficient," representing an estimated $48 billion in repairs, and 89,024 (12.2%) were rated "functionally obsolete," representing an estimated $91 billion in replacement costs.
A "bridge sufficiency rating" is calculated, which is based 55% on the structural evaluation, 30% on the obsolescence of its design, and 15% on its importance to the public.
[7] Since the NBI data is widely used by researchers and practitioners,[8][9] the Federal Highway Administration made it available in 2021 in a relational database, Long-Term Bridge Performance (LTBP).