What It Means
The National Bridge Inventory is a comprehensive database maintained by the Federal Highway Administration containing inspection and inventory data on every bridge longer than 20 feet carrying public roads in the United States. The inventory includes more than 617,000 bridges, spanning interstate highways, U.S. routes, state highways, county roads, city streets, and some tribal and federal lands roads. Each record contains more than 130 data items covering location (latitude, longitude, state, county, route), structural characteristics (material, design type, span count, length, width), condition ratings (deck, superstructure, substructure, culvert), load rating, traffic (ADT, truck percentage), historical significance, scour vulnerability, and inspection history. States are required under the National Bridge Inspection Standards to inspect each bridge at least every 24 months and submit annual updates to FHWA, typically by April 1 for the prior calendar year. FHWA compiles the submissions into a single bulk ASCII dataset released publicly each year, and BridgeWatch's scripts/fetch-nbi.ts pipeline downloads this file to populate condition scores and rankings. The NBI was established by the 1968 Federal-Aid Highway Act following the 1967 Silver Bridge collapse and has been continuously expanded ever since. It is the authoritative source for national bridge condition statistics, including the widely cited figure that approximately 7.5% of U.S. bridges are structurally deficient and that the average bridge is approximately 45 years old against a typical design life of 50-75 years. NBI data underpins federal funding allocations for the Highway Bridge Program and the IIJA bridge investment.
National Bridge Inventory (NBI) is one of the bridge-engineering or FHWA-policy concepts that recurs across BridgeSafety. Below is how the concept connects to the National Bridge Inventory data behind every page on the site.
Within the BridgeSafety Condition Score, each primary component (deck, superstructure, substructure) contributes about a third of the rating, with an age penalty applied to bridges past their typical design life. The methodology page describes the scoring in full detail.
Frequently Asked Questions
What does "National Bridge Inventory (NBI)" mean?
The federal database of all bridges on public roads in the United States, maintained by FHWA and updated annually.
Why does National Bridge Inventory (NBI) matter for bridge safety?
The National Bridge Inventory is a comprehensive database maintained by the Federal Highway Administration containing inspection and inventory data on every bridge longer than 20 feet carrying public roads in the United States. The inventory includes more than 617,000 bridges, spanning interstate hi...