US Bridges

I 15 over Sep Depot Hill Road

Fair

Jefferson County, Montana · Boulder · Structure no. I00015164+01431

Built
1973
52 years old
Condition
Fair
inspected November 2024
Type
Slab
Concrete Continuous
Length
83 ft
3 main spans
Daily traffic
1,928
2023 count
Owner
State
State Highway Agency

About this bridge

I 15 over Sep Depot Hill Road is a concrete continuous slab carrying I 15 over Sep Depot Hill Road in Jefferson County, Montana. It was built in 1973, so it is 52 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 1,928 vehicles a day, roughly 13% of them trucks, projected to reach 2,082 by 2043. The structure is 83 ft (25.3 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 Depot Hill Road
LocationBoulder
RouteInterstate 15
CountyJefferson County
StateMontana
Coordinates46.241, -112.13292
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.
Superstructure6 SatisfactoryStructural elements show some minor deterioration.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Last inspectionNovember 2024
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourBridge not over waterway
Structural evaluation6: Equal to present minimum criteria
Deck geometry7: Better than present minimum criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating39 US tons
Inventory rating30 US tons

Structure

Structure typeSlab
MaterialConcrete Continuous
DeckConcrete, cast-in-place
Main spans3
Design loadHS 20
Structure length83 ft (25.3 m)
Longest span83 ft (25.3 m)
Deck width44 ft (13.5 m)
Roadway width42 ft (12.7 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic1,928 (2023)
Projected traffic2,082 by 2043
Trucks13%
Lanes on structure2
Traffic directionOne-way traffic
CarriesHighway
CrossesHighway
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 Depot Hill Road built?

It was built in 1973, making it 52 years old in 2025.

What condition is I 15 over Sep Depot Hill Road 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 November 2024.

How much traffic does I 15 over Sep Depot Hill Road carry?

About 1,928 vehicles per day (2023 count), of which roughly 13% are trucks.

How long is I 15 over Sep Depot Hill Road?

The structure is 83 ft (25.3 m) long with a longest span of 83 ft (25.3 m) and a deck 44 ft wide.

Who owns I 15 over Sep Depot Hill Road?

It is owned by the State Highway Agency.