S 91
Carrying S 91 over BOULDER RIVER OVERFLOW
BIG TIMBER, Sweet Grass, Montana
Data updated May 2026
FHWA NBI record, refreshed with each annual release.
Bridge Snapshot: S 91
The S 91 bridge in Sweet Grass, Montana carries S 91 over BOULDER RIVER OVERFLOW. It was built in 1937, making it 89 years old today. The structure is built primarily of wood or timber and spans 1 section, stretching 7.6 meters (25 feet) end to end. Daily traffic averages 2,120 vehicles, placing it in the moderately-trafficked 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 4/9. The weakest component sits in poor condition. Because at least one major component scores 4 or lower, this bridge falls in FHWA's Poor condition category. That category is not a closure order. Its NBI inventory load rating is 31.8 metric tons.
Sourced from the FHWA National Bridge Inventory. See our methodology for refresh cadence and NBI release vintage.
How S 91 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 How the historical reference is calculated.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
- 1937
- Material
- Wood or Timber
- Number of Spans
- 1
- Structure Length
- 7.6 m (25 ft)
- Deck Width
- 10.3 m (34 ft)
- Owner
- State Highway Agency
- Avg Daily Traffic
- 2,120 vehicles/day
- Structure Number
- P00091002+06681
Location
Data Source
FHWA National Bridge Inventory (NBI).
FHWA NBI Program ↗Condition Analysis
- • At 6/9, the deck (driving surface) shows fair condition, with minor wear flagged for upkeep.
- • The superstructure (beams and supports above the deck) is in good condition (7/9), showing no significant deterioration.
- • The substructure (piers and abutments) is in poor condition (4/9), showing advanced deterioration that may require priority repair.
How to read this record
S 91 is in the federal Poor condition category. That is a component-based result, not a closure order.
- NBI condition ratings reflect the latest record in this annual dataset, not a live status. Current routine inspection intervals are risk-based.
- Understand what Poor condition does and does not mean before drawing conclusions. Poor condition explained
- Compare S 91 against other structures in Sweet Grass 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 S 91?
S 91 in Sweet Grass, Montana has a deck rating of 6/9, superstructure rating of 7/9, and substructure rating of 4/9 on the FHWA's 0–9 scale.
How often is S 91 inspected?
S 91'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 2,120 vehicles per day.
What does “structurally deficient” mean in older bridge reports?
FHWA retired that reported status beginning with the 2018 archive. S 91 is currently shown as Poor condition from its component ratings; that category is not a live closure or safety decision.
What is the inventory load rating for S 91?
S 91 has an NBI inventory load rating of 31.8 metric tons.
Who is responsible for maintaining S 91?
S 91 is owned and maintained by State Highway Agency.
How old is S 91 and does age affect safety?
S 91 was built in 1937, making it 89 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.