US Bridges

I 15 over Sep RR

Fair

Beaverhead County, Montana · 1.2M N Monida · Structure no. I00015001+05692

Built
1981
44 years old
Condition
Fair
inspected May 2023
Type
Stringer/Multi-beam or Girder
Prestressed Concrete
Length
253 ft
3 main spans
Daily traffic
1,771
2023 count
Owner
State
State Highway Agency

About this bridge

I 15 over Sep RR is a prestressed concrete stringer/multi-beam or girder carrying I 15 over Sep RR 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 1,771 vehicles a day, roughly 30% of them trucks, projected to reach 1,894 by 2043. The structure is 253 ft (77.1 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
CrossesSep RR
Location1.2M N Monida
RouteInterstate 15
CountyBeaverhead County
StateMontana
Coordinates44.5661, -112.33835
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.
Last inspectionMay 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourBridge not over waterway
Structural evaluation5: Somewhat better than minimum adequacy to tolerate being left in place as is
Deck geometry7: Better than present minimum criteria
Approach roadway alignment7: Better than present minimum criteria
Operating rating61 US tons
Inventory rating25 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialPrestressed Concrete
DeckConcrete, cast-in-place
Main spans3
Design loadHS 20
Structure length253 ft (77.1 m)
Longest span120 ft (36.6 m)
Deck width44 ft (13.4 m)
Roadway width41 ft (12.6 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic1,771 (2023)
Projected traffic1,894 by 2043
Trucks30%
Lanes on structure2
Traffic directionOne-way traffic
CarriesHighway
CrossesRailroad
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—
NavigationNot applicable (no waterway)

Frequently asked questions

When was I 15 over Sep RR built?

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

What condition is I 15 over Sep RR 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 May 2023.

How much traffic does I 15 over Sep RR carry?

About 1,771 vehicles per day (2023 count), of which roughly 30% are trucks.

How long is I 15 over Sep RR?

The structure is 253 ft (77.1 m) long with a longest span of 120 ft (36.6 m) and a deck 44 ft wide.

Who owns I 15 over Sep RR?

It is owned by the State Highway Agency.