US Bridges

I 15 over Int Dearborn-Missouri R

Fair

Cascade County, Montana · 6M N Craig · Structure no. I00015240+04151

Built
1971
54 years old
Condition
Fair
inspected June 2024
Type
Stringer/Multi-beam or Girder
Steel Continuous
Length
841 ft
3 main spans
Daily traffic
2,201
2023 count
Owner
State
State Highway Agency

About this bridge

I 15 over Int Dearborn-Missouri R is a steel continuous stringer/multi-beam or girder carrying I 15 over Int Dearborn-Missouri R in Cascade County, Montana. It was built in 1971, so it is 54 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 2,201 vehicles a day, roughly 16% of them trucks, projected to reach 2,343 by 2043. The structure is 841 ft (256.3 m) long and 41 ft wide. If it were closed, the detour would be 1.2 mi (2 km).

Location

Open in Google Maps
CarriesI 15
CrossesInt Dearborn-Missouri R
Location6M N Craig
RouteInterstate 15
CountyCascade County
StateMontana
Coordinates47.13279, -111.8869
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 protection8 Very GoodNo problems noted.
Last inspectionJune 2024
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 geometry6: Equal to present minimum criteria
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating30.3 US tons
Inventory rating23.6 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialSteel Continuous
DeckConcrete, cast-in-place
Main spans3 (+5 approach)
Design loadHS 20
Structure length841 ft (256.3 m)
Longest span180 ft (54.9 m)
Deck width41 ft (12.4 m)
Roadway width38 ft (11.6 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic2,201 (2023)
Projected traffic2,343 by 2043
Trucks16%
Lanes on structure2
Traffic directionOne-way traffic
CarriesOverpass structure at an interchange
CrossesHighway, waterway and railroad
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 Int Dearborn-Missouri R built?

It was built in 1971, making it 54 years old in 2025.

What condition is I 15 over Int Dearborn-Missouri R 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 June 2024.

How much traffic does I 15 over Int Dearborn-Missouri R carry?

About 2,201 vehicles per day (2023 count), of which roughly 16% are trucks.

How long is I 15 over Int Dearborn-Missouri R?

The structure is 841 ft (256.3 m) long with a longest span of 180 ft (54.9 m) and a deck 41 ft wide.

Who owns I 15 over Int Dearborn-Missouri R?

It is owned by the State Highway Agency.