US Bridges

I 90 over St. Regis River

Fair

Mineral County, Montana · 4.3M W St. Regis · Structure no. I00090029+02051

Built
1981
44 years old, rebuilt 2010
Condition
Fair
inspected July 2023
Type
Stringer/Multi-beam or Girder
Steel
Length
402 ft
4 main spans
Daily traffic
4,056
2023 count
Owner
State
State Highway Agency

About this bridge

I 90 over St. Regis River is a steel stringer/multi-beam or girder carrying I 90 over St. Regis River in Mineral County, Montana. It was built in 1981 and reconstructed in 2010, so it is 44 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 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 4,056 vehicles a day, roughly 24% of them trucks, projected to reach 4,258 by 2043. The structure is 402 ft (122.6 m) long and 44 ft wide. If it were closed, the detour would be 1.2 mi (2 km).

Location

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CarriesI 90
CrossesSt. Regis River
Location4.3M W St. Regis
RouteInterstate 90
CountyMineral County
StateMontana
Coordinates47.30103, -115.18213
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.
Superstructure5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Channel and channel protection6 SatisfactoryStructural elements show some minor deterioration.
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 geometry9: Superior to present desirable criteria
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating41 US tons
Inventory rating32 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialSteel
DeckConcrete, cast-in-place
Main spans4
Design loadHS 20
Structure length402 ft (122.6 m)
Longest span102 ft (31.1 m)
Deck width44 ft (13.5 m)
Roadway width43 ft (13 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic4,056 (2023)
Projected traffic4,258 by 2043
Trucks24%
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 90 over St. Regis River built?

It was built in 1981, making it 44 years old in 2025. It was reconstructed in 2010.

What condition is I 90 over St. Regis 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 90 over St. Regis River carry?

About 4,056 vehicles per day (2023 count), of which roughly 24% are trucks.

How long is I 90 over St. Regis River?

The structure is 402 ft (122.6 m) long with a longest span of 102 ft (31.1 m) and a deck 44 ft wide.

Who owns I 90 over St. Regis River?

It is owned by the State Highway Agency.