US Bridges

Shamrock Road over Boulder River

Fair

Jefferson County, Montana · 2 MI Past Whitehouse C. G · Structure no. 010207000003047

Built
1980
45 years old
Condition
Fair
inspected December 2024
Type
Stringer/Multi-beam or Girder
Wood or Timber
Length
28 ft
1 main span
Daily traffic
40
2018 count
Owner
Federal
U.S. Forest Service

About this bridge

Shamrock Road over Boulder River is a wood or timber stringer/multi-beam or girder carrying Shamrock Road over Boulder River in Jefferson County, Montana. It was built in 1980, so it is 45 years old, younger 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 6 out of 9. The lowest-rated primary component is rated 5 or 6. Minor deterioration is present but the structure is sound.

It carries about 40 vehicles a day, projected to reach 60 by 2045. The structure is 28 ft (8.6 m) long and 16 ft wide. If it were closed, the detour would be 620.7 mi (999 km).

Location

Open in Google Maps
CarriesShamrock Road
CrossesBoulder River
Location2 MI Past Whitehouse C. G
RouteFederal Lands Road 5046
CountyJefferson County
StateMontana
Coordinates46.25075, -112.51404
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
Deck7 GoodSome minor problems.
Superstructure7 GoodSome minor problems.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Channel and channel protection6 SatisfactoryStructural elements show some minor deterioration.
Last inspectionDecember 2024
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; action required to protect exposed foundations
Structural evaluation6: Equal to present minimum criteria
Deck geometry6: Equal to present minimum criteria
Waterway adequacy7: Better than present minimum criteria
Approach roadway alignment6: Equal to present minimum criteria
Operating rating40 US tons
Inventory rating31.1 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialWood or Timber
DeckWood or timber
Main spans1
Design loadHS 20
Structure length28 ft (8.6 m)
Longest span27 ft (8.2 m)
Deck width16 ft (4.9 m)
Roadway width14 ft (4.3 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic40 (2018)
Projected traffic60 by 2045
Trucks—
Lanes on structure1
Traffic directionOne-lane bridge for two-way traffic
CarriesHighway
CrossesWaterway
Detour if closed620.7 mi (999 km)
TollOn a free road
National Highway SystemNo

Ownership and planned work

OwnerU.S. Forest Service
Maintained byU.S. Forest Service
Historic statusHistorical significance not determinable at this time
Work proposedNone recorded
Estimated improvement cost—
NavigationNo navigation control on waterway

Frequently asked questions

When was Shamrock Road over Boulder River built?

It was built in 1980, making it 45 years old in 2025.

What condition is Shamrock Road over Boulder 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 December 2024.

How much traffic does Shamrock Road over Boulder River carry?

About 40 vehicles per day (2018 count).

How long is Shamrock Road over Boulder River?

The structure is 28 ft (8.6 m) long with a longest span of 27 ft (8.2 m) and a deck 16 ft wide.

Who owns Shamrock Road over Boulder River?

It is owned by the U.S. Forest Service.