US Bridges

I 15 over Big Hole River

Fair

Madison County, Montana · 7.4M S Melrose · Structure no. I00015085+06651

Built
1973
52 years old
Condition
Fair
inspected January 2024
Type
Stringer/Multi-beam or Girder
Steel Continuous
Length
445 ft
3 main spans
Daily traffic
1,926
2023 count
Owner
State
State Highway Agency

About this bridge

I 15 over Big Hole River is a steel continuous stringer/multi-beam or girder carrying I 15 over Big Hole River in Madison 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 1,926 vehicles a day, roughly 24% of them trucks, projected to reach 2,080 by 2043. The structure is 445 ft (135.6 m) long and 44 ft wide.

Location

Open in Google Maps
CarriesI 15
CrossesBig Hole River
Location7.4M S Melrose
RouteInterstate 15
CountyMadison County
StateMontana
Coordinates45.53035, -112.70346
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.
Channel and channel protection7 GoodSome minor problems.
Last inspectionJanuary 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 geometry7: Better than present minimum criteria
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating44.6 US tons
Inventory rating34.3 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialSteel Continuous
DeckConcrete, cast-in-place
Main spans3 (+2 approach)
Design loadHS 20
Structure length445 ft (135.6 m)
Longest span115 ft (35.1 m)
Deck width44 ft (13.4 m)
Roadway width41 ft (12.6 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic1,926 (2023)
Projected traffic2,080 by 2043
Trucks24%
Lanes on structure2
Traffic directionOne-way traffic
CarriesHighway
CrossesWaterway
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—
NavigationNo navigation control on waterway

Frequently asked questions

When was I 15 over Big Hole River built?

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

What condition is I 15 over Big Hole 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 2024.

How much traffic does I 15 over Big Hole River carry?

About 1,926 vehicles per day (2023 count), of which roughly 24% are trucks.

How long is I 15 over Big Hole River?

The structure is 445 ft (135.6 m) long with a longest span of 115 ft (35.1 m) and a deck 44 ft wide.

Who owns I 15 over Big Hole River?

It is owned by the State Highway Agency.