IRR - S 451
Carrying IRR - S 451 over LODGE GRASS CREEK
LODGE GRASS, Big Horn, Montana
Data updated May 2026
FHWA NBI record, refreshed with each annual release.
Bridge Snapshot: IRR - S 451
The IRR - S 451 bridge in Big Horn, Montana carries IRR - S 451 over LODGE GRASS CREEK. It was built in 1955, making it 71 years old today. The structure is built primarily of concrete continuous and spans 3 sections, stretching 19.7 meters (65 feet) end to end. Daily traffic averages 536 vehicles, placing it in the lower-traffic tier of Montana bridges. It is owned and maintained by State Highway Agency.
The latest FHWA inspection records show a deck rating of 6/9, superstructure at 7/9, substructure at 7/9. The weakest component sits in fair condition. No reported major component scores in the Poor range under the current federal condition thresholds. Its NBI inventory load rating is 29.9 metric tons.
Sourced from the FHWA National Bridge Inventory. See our methodology for refresh cadence and NBI release vintage.
How IRR - S 451 compares
Live comparison across Montana.
Historical Sufficiency Rating
PlainBridge-computedFHWA discontinued this calculated item; it does not determine current condition, funding eligibility, posting, or closure. How the historical reference is calculated.
Condition Ratings
Full 0–9 scale + sufficiency-rating breakdown: how condition ratings work.
Structural Details
- Year Built
- 1955
- Material
- Concrete Continuous
- Number of Spans
- 3
- Structure Length
- 19.7 m (65 ft)
- Deck Width
- 10.8 m (35 ft)
- Owner
- State Highway Agency
- Avg Daily Traffic
- 536 vehicles/day
- Structure Number
- S00451015+07741
Location
Data Source
FHWA National Bridge Inventory (NBI).
FHWA NBI Program ↗Condition Analysis
- • The deck (driving surface) rates fair at 6/9, minor deterioration that routine maintenance should address.
- • The superstructure (beams and supports above the deck) rates good at 7/9, with no significant deterioration on file.
- • At 7/9, the substructure (piers and abutments) is in good shape and shows no significant wear.
How to read this record
This page shows what the last federal inspection recorded, not whether IRR - S 451 is safe to cross today. Here is how to use it.
- NBI condition ratings reflect the latest record in this annual dataset, not a live status. Current routine inspection intervals are risk-based.
- Learn how the 0–9 condition scale and Good/Fair/Poor categories are defined. How condition ratings work
- Compare IRR - S 451 against other structures in Big Horn and across Montana. Montana bridges
- Noticed visible damage or a safety concern? Report it to the agency that owns the bridge, or call 911 in an emergency. How to report a bridge
Condition codes come straight from the FHWA National Bridge Inventory and are not a real-time safety judgment. Only the owning agency, a state DOT, county, or other owner, can post, restrict, or close a bridge.
Frequently Asked Questions
What do the condition ratings mean for IRR - S 451?
IRR - S 451 in Big Horn, Montana has a deck rating of 6/9, superstructure rating of 7/9, and substructure rating of 7/9 on the FHWA's 0–9 scale.
How often is IRR - S 451 inspected?
IRR - S 451's responsible agency sets its routine interval under FHWA's risk-based inspection rules; this page does not expose the scheduled interval. It carries about 536 vehicles per day.
What does “structurally deficient” mean in older bridge reports?
FHWA retired that reported status beginning with the 2018 archive. IRR - S 451 is currently shown as Fair condition from its component ratings; that category is not a live closure or safety decision.
What is the inventory load rating for IRR - S 451?
IRR - S 451 has an NBI inventory load rating of 29.9 metric tons.
Who is responsible for maintaining IRR - S 451?
IRR - S 451 is owned and maintained by State Highway Agency.
How old is IRR - S 451 and does age affect safety?
IRR - S 451 was built in 1955, making it 71 years old.
Disclaimer: Bridge condition data is from the FHWA NBI and reflects the last reported inspection. A Poor condition rating is not a live declaration that a bridge is closed or unsafe for travel. For current closure, posting, or safety information, contact the responsible transportation agency.
Every figure on PlainBridge is rendered directly from federal source data, no number is typed in by an editor. This page draws directly on federal source data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.