US Bridges

I 15 over Red Rock River

Fair

Beaverhead County, Montana · 6.2M S Clark Canyon Dam · Structure no. I00015038+04302

Built
1981
44 years old
Condition
Fair
inspected January 2025
Type
Stringer/Multi-beam or Girder
Prestressed Concrete
Length
174 ft
2 main spans
Daily traffic
2,116
2023 count
Owner
State
State Highway Agency

About this bridge

I 15 over Red Rock River is a prestressed concrete stringer/multi-beam or girder carrying I 15 over Red Rock River in Beaverhead County, Montana. It was built in 1981, so it is 44 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 2,116 vehicles a day, roughly 25% of them trucks, projected to reach 2,264 by 2043. The structure is 174 ft (52.9 m) long and 44 ft wide. If it were closed, the detour would be 1.2 mi (2 km).

Location

Open in Google Maps
CarriesI 15
CrossesRed Rock River
Location6.2M S Clark Canyon Dam
RouteInterstate 15
CountyBeaverhead County
StateMontana
Coordinates44.91597, -112.8245
Functional classRural Principal Arterial - Interstate

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.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Channel and channel protection7 GoodSome minor problems.
Last inspectionJanuary 2025
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour within limits of footing or piles
Structural evaluation5: Somewhat better than minimum adequacy to tolerate being left in place as is
Deck geometry7: Better than present minimum criteria
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating56 US tons
Inventory rating24 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialPrestressed Concrete
DeckConcrete, cast-in-place
Main spans2
Design loadHS 20
Structure length174 ft (52.9 m)
Longest span106 ft (32.4 m)
Deck width44 ft (13.5 m)
Roadway width41 ft (12.6 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic2,116 (2023)
Projected traffic2,264 by 2043
Trucks25%
Lanes on structure2
Traffic directionOne-way traffic
CarriesHighway
CrossesWaterway
Detour if closed1.2 mi (2 km)
TollOn a free road
National Highway SystemYes
Strategic Highway NetworkInterstate STRAHNET route

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 I 15 over Red Rock River built?

It was built in 1981, making it 44 years old in 2025.

What condition is I 15 over Red Rock 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 January 2025.

How much traffic does I 15 over Red Rock River carry?

About 2,116 vehicles per day (2023 count), of which roughly 25% are trucks.

How long is I 15 over Red Rock River?

The structure is 174 ft (52.9 m) long with a longest span of 106 ft (32.4 m) and a deck 44 ft wide.

Who owns I 15 over Red Rock River?

It is owned by the State Highway Agency.