US Bridges

I 15 over Boulder River

Fair

Jefferson County, Montana · 1.9M W Boulder · Structure no. I00015161+09101

Built
1980
45 years old
Condition
Fair
inspected July 2023
Type
Stringer/Multi-beam or Girder
Prestressed Concrete
Length
184 ft
3 main spans
Daily traffic
1,928
2023 count
Owner
State
State Highway Agency

About this bridge

I 15 over Boulder River is a prestressed concrete stringer/multi-beam or girder carrying I 15 over Boulder River in Jefferson County, Montana. It was built in 1980, so it is 45 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 1,928 vehicles a day, roughly 13% of them trucks, projected to reach 2,082 by 2043. The structure is 184 ft (56.1 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
CrossesBoulder River
Location1.9M W Boulder
RouteInterstate 15
CountyJefferson County
StateMontana
Coordinates46.24513, -112.17214
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
Deck7 GoodSome minor problems.
Superstructure7 GoodSome minor problems.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Channel and channel protection8 Very GoodNo problems noted.
Last inspectionJuly 2023
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 rating30 US tons
Inventory rating23 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialPrestressed Concrete
DeckConcrete, cast-in-place
Main spans3
Design loadHS 20
Structure length184 ft (56.1 m)
Longest span106 ft (32.3 m)
Deck width44 ft (13.5 m)
Roadway width41 ft (12.6 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
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 Boulder River built?

It was built in 1980, making it 45 years old in 2025.

What condition is I 15 over Boulder 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 July 2023.

How much traffic does I 15 over Boulder River carry?

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

How long is I 15 over Boulder River?

The structure is 184 ft (56.1 m) long with a longest span of 106 ft (32.3 m) and a deck 44 ft wide.

Who owns I 15 over Boulder River?

It is owned by the State Highway Agency.