US Bridges

I 15 over Int Basin

Fair

Jefferson County, Montana · Basin · Structure no. I00015156+09111

Built
1985
40 years old
Condition
Fair
inspected November 2024
Type
Stringer/Multi-beam or Girder
Steel
Length
133 ft
3 main spans
Daily traffic
3,856
2023 count
Owner
State
State Highway Agency

About this bridge

I 15 over Int Basin is a steel stringer/multi-beam or girder carrying I 15 over Int Basin in Jefferson County, Montana. It was built in 1985, so it is 40 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 3,856 vehicles a day, roughly 13% of them trucks, projected to reach 4,164 by 2043. The structure is 133 ft (40.5 m) long and 84 ft wide.

Location

Open in Google Maps
CarriesI 15
CrossesInt Basin
LocationBasin
RouteInterstate 15
CountyJefferson County
StateMontana
Coordinates46.27139, -112.2473
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 inspectionNovember 2024
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourBridge not over waterway
Structural evaluation6: Equal to present minimum criteria
Deck geometry9: Superior to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating51.5 US tons
Inventory rating39.7 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialSteel
DeckConcrete, cast-in-place
Main spans3
Design loadHS 20
Structure length133 ft (40.5 m)
Longest span52 ft (15.7 m)
Deck width84 ft (25.7 m)
Roadway width79 ft (24.2 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic3,856 (2023)
Projected traffic4,164 by 2043
Trucks13%
Lanes on structure4
Traffic directionTwo-way traffic
CarriesOverpass structure at an interchange
CrossesHighway
Detour if closed—
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 Int Basin built?

It was built in 1985, making it 40 years old in 2025.

What condition is I 15 over Int Basin 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 Int Basin carry?

About 3,856 vehicles per day (2023 count), of which roughly 13% are trucks.

How long is I 15 over Int Basin?

The structure is 133 ft (40.5 m) long with a longest span of 52 ft (15.7 m) and a deck 84 ft wide.

Who owns I 15 over Int Basin?

It is owned by the State Highway Agency.