The Federal Highway Administration (FHWA) maintains the National Bridge Inventory (NBI), a database of every road bridge longer than 20 feet in the United States. There are roughly 620,000 of them. Each one is inspected at least every two years, more often if it's in poor condition, and every inspection is rated against a standardized federal scale. The data is public, free to look up, and surprisingly few people know how to read it.
What the National Bridge Inventory contains
For each bridge in the U.S. road network, the NBI records: location coordinates, the road carried and the feature crossed (river, railroad, another road), year built, year reconstructed, length, lane count, average daily traffic, design type, structural materials, and most importantly, condition ratings for the deck, superstructure, and substructure.
The condition ratings are on a 0-to-9 scale where 9 is excellent and 0 is failed. The thresholds:
- 9 — Excellent condition. New or like-new.
- 8 — Very good condition. No problems noted.
- 7 — Good condition. Minor problems.
- 6 — Satisfactory condition. Structural elements show minor deterioration.
- 5 — Fair condition. Minor section loss, cracking, spalling, or scour.
- 4 — Poor condition. Advanced section loss, deterioration, spalling, or scour.
- 3 — Serious condition. Loss of section, deterioration, spalling, or scour seriously affected primary structural components.
- 2 — Critical condition. Advanced deterioration of primary structural elements; bridge may be closed until repaired.
- 1 — Imminent failure condition. Major deterioration or section loss; bridge closed but corrective action may put it back in light service.
- 0 — Failed condition. Bridge out of service, beyond corrective action.
What "structurally deficient" means
"Structurally deficient" is a specific federal classification. A bridge is classified structurally deficient if any one of its primary load-carrying components — deck, superstructure, or substructure — has a rating of 4 or below.
The term has been controversial. It is regularly cited in news articles after a bridge collapse to suggest that thousands of "structurally deficient" bridges are at risk of falling down. That overstates what the rating actually means. A structurally deficient bridge is one that needs significant maintenance or rehabilitation; in most cases, it is still safe to drive over, possibly with weight restrictions or speed limits. Bridges that are actually unsafe are closed (rating 0–2) or weight-restricted, not just classified.
The accurate read: structurally deficient = needs rehabilitation, not at risk of imminent collapse. About 7 percent of U.S. bridges are currently structurally deficient by this definition.
"Functionally obsolete"
A separate classification, retired in 2018 from the FHWA's primary metrics but still appearing in older literature. A bridge was classified functionally obsolete if its design no longer met current standards — too narrow for modern traffic, low vertical clearance, inadequate guardrails, etc. — even if its structural condition was sound.
Functionally obsolete is a comfort and traffic-flow issue, not primarily a safety issue. A 1920s-era stone-arch bridge that is too narrow for two trucks to pass is functionally obsolete; the bridge itself may be in fine structural condition. The FHWA dropped this term from its primary categorization in 2018 because it was being conflated with structural deficiency in public discourse.
"Scour critical"
A separate flag worth understanding. Scour is the erosion of riverbed material around bridge piers caused by water flow, particularly during floods. A bridge classified "scour critical" has a foundation that has been determined to be vulnerable to scour during flood conditions.
Scour critical is not the same as structurally deficient. The bridge might be in fine condition right now; it just has a foundation type and location that makes it vulnerable to a flood-driven failure. Most scour-critical bridges have countermeasures — riprap, scour aprons, real-time flood monitoring — that mitigate the risk.
The 1987 Schoharie Creek bridge collapse in upstate New York and the 2005 collapse of the I-90 bridge in New York were both scour-related. Both spurred more aggressive scour monitoring; the proportion of bridges classified scour critical has decreased over time as countermeasures have been added or older bridges have been replaced.
Looking up bridges on your commute
Every NBI inspection is public. You can look up bridges by location, by route number, or by structure number. Each bridge's record includes:
- Year built and year of last major rehabilitation.
- Average daily traffic (ADT) — how many vehicles cross daily.
- Length and lane count.
- Current condition ratings for deck, superstructure, and substructure.
- Year of last inspection.
- Whether it's classified structurally deficient or scour critical.
The most useful query for most people: find the bridges within a few miles of your home or workplace, sorted by condition rating. You'll typically find a mix — most are in good or satisfactory condition, a handful might be in fair or poor condition. Knowing which ones are which is the kind of information that's useful to have but rarely gets surfaced unless you go looking for it.
Why bridge condition lags maintenance funding
Bridges are expensive to rehabilitate. A typical state DOT carries hundreds of bridges in fair-to-poor condition at any given time, and the funding to address them is allocated annually through state and federal budget cycles. The result is that condition ratings tend to drift downward slowly — a bridge classified satisfactory five years ago may be classified fair today, and may be classified poor in another five years, even with regular maintenance.
Bridge replacements typically follow predictable triggers: when condition reaches rating 3 or 4 and the cost of further maintenance starts approaching the cost of replacement, the bridge gets scheduled for replacement in the state's STIP (Statewide Transportation Improvement Program). The replacement might take 2–5 years to design, fund, bid, and build. Major bridge replacements (interstate-grade structures) can take a decade.
What to do if you're worried about a specific bridge
If a bridge near you is in poor or serious condition (rating 3 or 4) and you're concerned, the right channel is the state DOT, not the federal government. State DOTs are the inspecting and maintaining authority for nearly all U.S. bridges. They publish the inspection reports, schedule the rehabilitations, and make the call on weight restrictions and closures.
If a bridge is showing visible signs of distress — large spalls, exposed rebar, sagging, water flowing through the structure — that's worth reporting. State DOTs typically have a public-facing hotline for bridge concerns; the report goes to the bridge inspection unit, who will check the inspection record and dispatch a follow-up inspection if warranted.
Most of the time, when concerned citizens report a bridge problem, the response is "we're aware of it, it's monitored, here is the planned remediation." That's not dismissive — that's the system working. The inspection regime is designed to catch problems early, well before they become safety issues.