US Bridges

I 15 over Rr-Missouri River

Fair

Cascade County, Montana · 8M S Cascade · Structure no. I00015246+04051

Built
1968
57 years old
Condition
Fair
inspected June 2024
Type
Girder and Floorbeam System
Steel Continuous
Length
739 ft
3 main spans
Daily traffic
2,201
2023 count
Owner
State
State Highway Agency

About this bridge

I 15 over Rr-Missouri River is a steel continuous girder and floorbeam system carrying I 15 over Rr-Missouri River in Cascade County, Montana. It was built in 1968, so it is 57 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 5 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 739 ft (225.2 m) long and 33 ft wide.

Location

Open in Google Maps
CarriesI 15
CrossesRr-Missouri River
Location8M S Cascade
RouteInterstate 15
CountyCascade County
StateMontana
Coordinates47.17772, -111.81247
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
Deck5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
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 above top of footing
Structural evaluation6: Equal to present minimum criteria
Deck geometry4: Meets minimum tolerable limits to be left in place as is
Waterway adequacy9: Superior to present desirable criteria
Approach roadway alignment7: Better than present minimum criteria
Operating rating48.2 US tons
Inventory rating28.9 US tons

Structure

Structure typeGirder and Floorbeam System
MaterialSteel Continuous
DeckConcrete, cast-in-place
Main spans3 (+4 approach)
Design loadHS 20
Structure length739 ft (225.2 m)
Longest span154 ft (46.9 m)
Deck width33 ft (10.1 m)
Roadway width31 ft (9.3 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
CarriesHighway
CrossesRailroad and waterway
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 Rr-Missouri River built?

It was built in 1968, making it 57 years old in 2025.

What condition is I 15 over Rr-Missouri 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 June 2024.

How much traffic does I 15 over Rr-Missouri River carry?

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

How long is I 15 over Rr-Missouri River?

The structure is 739 ft (225.2 m) long with a longest span of 154 ft (46.9 m) and a deck 33 ft wide.

Who owns I 15 over Rr-Missouri River?

It is owned by the State Highway Agency.