S 91 over Boulder River Overflow
Sweet Grass County, Montana · rated Poor in the 2025 National Bridge Inventory
United States Bridge Conditions2025 National Bridge Inventory, FHWACompiled
- S 91 over Boulder River Overflow in Sweet Grass County, Montana, is rated in poor condition in the 2025 National Bridge Inventory (as of ).
- It was built in 1937, making it 88 years old at the 2025 inventory.
- It carries about 2,133 vehicles a day (traffic count year 2023).
- Its listed owner is the state highway agency.
- A poor rating means at least one major component - deck, superstructure, or substructure - is rated 4 or lower on FHWA's 0-9 scale. It does not by itself mean the bridge is unsafe; bridges judged unsafe are closed or load-restricted by their owners.
View this bridge on a map → (45.83461, -109.93522)
Component ratings
| Component | Rating (2025) | FHWA scale meaning |
|---|---|---|
| Deck | 6 | Satisfactory condition |
| Superstructure | 7 | Good condition |
| Substructure | 4 | Poor condition |
Bridge details
| Structure | Timber stringer or multi-beam girder |
| Length | about 25 ft |
| Location | Big Timber |
| NBI structure number | P00091002+06681 |
Source: FHWA National Bridge Inventory, 2025 data as reported by the Montana department of transportation.
All bridges nearby: Sweet Grass County, MT bridge conditions · Montana bridges.
Background: how bridge ratings work · what "poor" and "structurally deficient" actually mean · how often bridges are inspected.