US Bridges

Main Boulder RD over West Boulder River

Fair

Sweet Grass County, Montana · Mcleod · Structure no. S00298016+03261

Built
1976
49 years old
Condition
Fair
inspected March 2024
Type
Stringer/Multi-beam or Girder
Prestressed Concrete
Length
153 ft
3 main spans
Daily traffic
529
2023 count
Owner
State
State Highway Agency

About this bridge

Main Boulder RD over West Boulder River is a prestressed concrete stringer/multi-beam or girder carrying Main Boulder RD over West Boulder River in Sweet Grass County, Montana. It was built in 1976, so it is 49 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 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 529 vehicles a day, roughly 5% of them trucks, projected to reach 555 by 2043. The structure is 153 ft (46.6 m) long and 34 ft wide. If it were closed, the detour would be 98.2 mi (158 km).

Location

Open in Google Maps
CarriesMain Boulder RD
CrossesWest Boulder River
LocationMcleod
RouteState Highway 298
CountySweet Grass County
StateMontana
Coordinates45.66096, -110.11342
Functional classRural Major Collector

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.
Superstructure7 GoodSome minor problems.
Substructure7 GoodSome minor problems.
Channel and channel protection7 GoodSome minor problems.
Last inspectionMarch 2024
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour within limits of footing or piles
Structural evaluation6: Equal to present minimum criteria
Deck geometry6: Equal to present minimum criteria
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating52 US tons
Inventory rating26 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialPrestressed Concrete
DeckConcrete, cast-in-place
Main spans3
Design loadHS 20
Structure length153 ft (46.6 m)
Longest span71 ft (21.6 m)
Deck width34 ft (10.5 m)
Roadway width31 ft (9.6 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic529 (2023)
Projected traffic555 by 2043
Trucks5%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed98.2 mi (158 km)
TollOn a free road
National Highway SystemNo

Ownership and planned work

OwnerState Highway Agency
Maintained byState Highway Agency
Historic statusNot eligible for the National Register of Historic Places
Work proposedNone recorded
Estimated improvement cost—
NavigationNo navigation control on waterway

Frequently asked questions

When was Main Boulder RD over West Boulder River built?

It was built in 1976, making it 49 years old in 2025.

What condition is Main Boulder RD over West 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 March 2024.

How much traffic does Main Boulder RD over West Boulder River carry?

About 529 vehicles per day (2023 count), of which roughly 5% are trucks.

How long is Main Boulder RD over West Boulder River?

The structure is 153 ft (46.6 m) long with a longest span of 71 ft (21.6 m) and a deck 34 ft wide.

Who owns Main Boulder RD over West Boulder River?

It is owned by the State Highway Agency.