Methodology & Data Sources

Data Source

All bridge data on PlainBridges comes from the Federal Highway Administration (FHWA) National Bridge Inventory (NBI) - the federal database mandated by Congress since 1968 following the Silver Bridge collapse. Every public highway bridge over 20 feet in the U.S. is required to be inspected and reported to the NBI.

Source URL: fhwa.dot.gov/bridge/nbi.cfm

Coverage

PlainBridges covers public highway bridges across all 50 states plus territories, sourced from the most recent annual NBI dataset.

How We Process the Data

1. Download the annual NBI dataset from FHWA
2. Parse all 116 NBI data items including condition ratings, structural details, traffic counts, and geographic data
3. Derive FHWA's current Good/Fair/Poor condition category from the lowest applicable component rating
4. Organize into searchable pages by bridge, county, and state

Condition Ratings Explained

FHWA inspectors rate four bridge components on a 0–9 scale:

• Deck - The road surface and supporting structure
• Superstructure - Beams, trusses, and spans that carry the load
• Substructure - Piers, abutments, and foundations
• Culvert - For pipe/box structures carrying drainage

A bridge is classified as Good if its lowest applicable component rating is 7 or above, Fair if the lowest is 5 or 6, and Poor if the lowest is 4 or below. These are the condition categories FHWA currently reports. “Structurally deficient” is a legacy term: FHWA eliminated that status from program use beginning with the 2018 archive and adopted Poor condition for this component-based result.

Load rating vs. sufficiency rating

Each bridge page shows the NBI inventory load rating (item 66) - the load level, in metric tons, a structure is rated to carry for an indefinite period. A lower number means the bridge is more load-restricted. This is a real, reported NBI field and is distinct from the FHWA sufficiency rating.

The sufficiency rating is a discontinued composite 0–100 score built from structural adequacy, functional obsolescence, essentiality to public use, and special reductions. FHWA's current SNBI no longer reports the calculated Sufficiency Rating or Status items. PlainBridges therefore labels any displayed sufficiency rating as a historical, PlainBridges-recomputed reference, calculated with Appendix B of the former Recording & Coding Guide. It does not determine a bridge's current Good/Fair/Poor category, funding eligibility, posting, or closure status. Where a bridge is missing an input the historical formula needs, we leave the rating blank rather than estimate it.

Data Currency

FHWA releases updated NBI data annually, typically in spring covering the prior calendar year. Routine inspection intervals are set under current risk-based NBIS rules; 24 months is common, with shorter or approved extended intervals for qualifying bridges. We update our database when a new annual NBI release is ingested.

Limitations

• Condition data reflects the most recent NBI inspection, which may lag current conditions by up to a year
• A Poor rating is a condition category, not a live declaration that a bridge is closed or unsafe to cross
• NBI does not cover pedestrian-only bridges, rail bridges, or bridges under 20 feet
• For current closure, load restriction, or emergency information, contact your state DOT

How the Source Agency Collects Data

The National Bridge Inventory is maintained by the Federal Highway Administration under the authority of the National Bridge Inspection Standards (NBIS), established by the Federal-Aid Highway Act of 1968. State transportation departments, Federal agencies, and Tribal governments set routine inspection intervals under FHWA's risk-based rules, using qualified bridge-inspection personnel. Inspectors evaluate standardized data items per bridge, including structural condition ratings, load capacity, geometric dimensions, and traffic volumes. The 2024 archive used the former Recording and Coding Guide; current reporting transitions to the Specifications for the National Bridge Inventory (SNBI).

States submit their inspection data annually to FHWA, which compiles it into the national NBI dataset. The FHWA publishes this dataset each spring, covering inspections from the prior calendar year. The U.S. Bureau of Transportation Statistics (BTS) publishes annual bridge condition summaries derived from the same NBI feed, and the U.S. Department of Transportation uses NBI condition data to allocate Highway Bridge Program funding under MAP-21 and the Infrastructure Investment and Jobs Act.

Data Accuracy Commitment

PlainBridges displays reported NBI fields and clearly labels its own derivations. Condition ratings and inventory load ratings come from the source records; Good/Fair/Poor categories, geographic rollups, percentiles, and the historical sufficiency reference are computed from those fields using the rules documented above. State pages also show a national ordinal on Poor-condition share (lower share ranks better among states and territories with a recorded rate). County pages show an in-state ordinal on the same share among counties with at least five public highway bridges, with ties broken by larger inventory then stable slug. None is an independent engineering or real-time safety assessment. If you find data that appears incorrect, please contact us and we will verify it against the NBI source record and our derivation.

Data reuse and citation

• CSV downloads (live): national-bridge-statistics.csv (state rollups matching /statistics) and high-traffic-poor-bridges.csv (high-AADT Poor-condition extract). Free to reuse with attribution to PlainBridges and FHWA NBI.
• Embeds: charts and tables on bridge, county, and state pages are rendered HTML with named NBI fields. We do not offer third-party iframe embeds today.
• Commercial data licensing, API access, and bulk extracts beyond the published CSVs are not activated; contact us if you need a custom arrangement.

Monetization and partnership readiness

Readiness only: nothing below activates revenue without operator review. PlainBridges is in the AdSense getting-ready queue for display advertising. If approved, ad units would follow Module 36 density ceilings and would never sit adjacent to interpretive safety advice (this site publishes registry-style NBI condition and inventory figures only; a Poor rating is not a live closure declaration). YMYL-compliant affiliate or referral placements are not live; any future activation would require clearly labeled, non-advice adjacency and operator sign-off. Alternative ad-network eligibility paperwork may be prepared against standard infrastructure-data publisher criteria (for example Media.net content guidelines), but activation remains operator-gated.

Contact

Questions about our methodology or found a data error? Reach us at hello@plainbridges.com or through our contact page.