US Bridges

18131: Maiden Rock over Big Hole River

FairPosted for load

Silver Bow County, Montana · 24 MI SW of Butte Mt · Structure no. 000000000L59197

Built
1951
74 years old, rebuilt 1993
Condition
Fair
inspected August 2024
Type
Truss - Thru
Steel
Length
202 ft
1 main span
Daily traffic
25
2022 count
Owner
Federal
Bureau of Land Management

About this bridge

18131: Maiden Rock over Big Hole River is a steel truss - thru carrying 18131: Maiden Rock over Big Hole River in Silver Bow County, Montana. It was built in 1951 and reconstructed in 1993, so it is 74 years old, older than the Montana average of 47 years.

The most recent inspection reported to the Federal Highway Administration rates it in fair condition with a lowest component rating of 5 out of 9. The lowest-rated primary component is rated 5 or 6. Minor deterioration is present but the structure is sound. Its operating status is: posted for load restriction.

It carries about 25 vehicles a day, projected to reach 50 by 2040. The structure is 202 ft (61.6 m) long and 21 ft wide. If it were closed, the detour would be 5 mi (8 km).

Location

Open in Google Maps
Carries18131: Maiden Rock
CrossesBig Hole River
Location24 MI SW of Butte Mt
RouteFederal Lands Road 0
CountySilver Bow County
StateMontana
Coordinates45.70152, -112.73534
Functional classRural Local

Condition and inspection

Fair

The lowest-rated primary component is rated 5 or 6. Minor deterioration is present but the structure is sound.

ComponentRatingMeaning
Deck6 SatisfactoryStructural elements show some minor deterioration.
Superstructure5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Substructure7 GoodSome minor problems.
Channel and channel protection7 GoodSome minor problems.
Last inspectionAugust 2024
Inspection intervalevery 24 months
Operating statusPosted for load restriction
ScourFoundations stable; scour within limits of footing or piles
Structural evaluation4: Meets minimum tolerable limits to be left in place as is
Deck geometry3: Basically intolerable, requiring high priority of corrective action
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment6: Equal to present minimum criteria
Operating rating16.4 US tons
Inventory rating12.5 US tons

Structure

Structure typeTruss - Thru
MaterialSteel
DeckCorrugated steel
Main spans1
Design loadHS 20
Structure length202 ft (61.6 m)
Longest span198 ft (60.4 m)
Deck width21 ft (6.4 m)
Roadway width16 ft (4.8 m)
Vertical clearance over deck2 ft (0.5 m)

Traffic and service

Average daily traffic25 (2022)
Projected traffic50 by 2040
Trucks—
Lanes on structure1
Traffic directionOne-lane bridge for two-way traffic
CarriesHighway
CrossesWaterway
Detour if closed5 mi (8 km)
TollOn a free road
National Highway SystemNo

Ownership and planned work

OwnerBureau of Land Management
Maintained byBureau of Land Management
Historic statusHistorical significance not determinable at this time
Work proposedOther structural work, including hydraulic replacements
Estimated improvement cost$40,000 (2018 estimate)
NavigationNo navigation control on waterway

Frequently asked questions

When was 18131: Maiden Rock over Big Hole River built?

It was built in 1951, making it 74 years old in 2025. It was reconstructed in 1993.

What condition is 18131: Maiden Rock over Big Hole River in?

The National Bridge Inventory rates it in fair condition. The lowest-rated primary component is rated 5 or 6. Minor deterioration is present but the structure is sound. The last reported inspection was in August 2024.

How much traffic does 18131: Maiden Rock over Big Hole River carry?

About 25 vehicles per day (2022 count).

How long is 18131: Maiden Rock over Big Hole River?

The structure is 202 ft (61.6 m) long with a longest span of 198 ft (60.4 m) and a deck 21 ft wide.

Who owns 18131: Maiden Rock over Big Hole River?

It is owned by the Bureau of Land Management.