S 91 over Boulder River Overflow
PoorSweet Grass County, Montana · Big Timber · Structure no. P00091002+06681
- Built
- 1937
- 88 years old
- Condition
- Poor
- inspected October 2024
- Type
- Stringer/Multi-beam or Girder
- Wood or Timber
- Length
- 26 ft
- 1 main span
- Daily traffic
- 2,133
- 2023 count
- Owner
- State
- State Highway Agency
About this bridge
S 91 over Boulder River Overflow is a wood or timber stringer/multi-beam or girder carrying S 91 over Boulder River Overflow in Sweet Grass County, Montana. It was built in 1937, so it is 88 years old, older than the Montana average of 47 years.
The most recent inspection reported to the Federal Highway Administration rates it in poor condition with a lowest component rating of 4 out of 9. The lowest-rated primary component is rated 4 or below, indicating advanced deterioration. Poor does not mean unsafe; such bridges are inspected more often and may carry load restrictions.
It carries about 2,133 vehicles a day, roughly 5% of them trucks, projected to reach 2,240 by 2043. The structure is 26 ft (7.8 m) long and 34 ft wide. If it were closed, the detour would be 6.8 mi (11 km).
Location
Open in Google MapsCondition and inspection
The lowest-rated primary component is rated 4 or below, indicating advanced deterioration. Poor does not mean unsafe; such bridges are inspected more often and may carry load restrictions.
| Component | Rating | Meaning |
|---|---|---|
| Deck | 6 Satisfactory | Structural elements show some minor deterioration. |
| Superstructure | 7 Good | Some minor problems. |
| Substructure | 4 Poor | Advanced section loss, deterioration, spalling or scour. |
| Channel and channel protection | 8 Very Good | No problems noted. |
Structure
Traffic and service
Ownership and planned work
Frequently asked questions
When was S 91 over Boulder River Overflow built?
It was built in 1937, making it 88 years old in 2025.
What condition is S 91 over Boulder River Overflow in?
The National Bridge Inventory rates it in poor condition. The lowest-rated primary component is rated 4 or below, indicating advanced deterioration. Poor does not mean unsafe; such bridges are inspected more often and may carry load restrictions. The last reported inspection was in October 2024.
How much traffic does S 91 over Boulder River Overflow carry?
About 2,133 vehicles per day (2023 count), of which roughly 5% are trucks.
How long is S 91 over Boulder River Overflow?
The structure is 26 ft (7.8 m) long with a longest span of 25 ft (7.5 m) and a deck 34 ft wide.
Who owns S 91 over Boulder River Overflow?
It is owned by the State Highway Agency.