US Bridges

I 90 over Int Phosphate

Fair

Powell County, Montana · 3.7M W Garrison · Structure no. I00090170+02411

Built
1973
52 years old
Condition
Fair
inspected October 2023
Type
Stringer/Multi-beam or Girder
Prestressed Concrete
Length
128 ft
3 main spans
Daily traffic
5,136
2023 count
Owner
State
State Highway Agency

About this bridge

I 90 over Int Phosphate is a prestressed concrete stringer/multi-beam or girder carrying I 90 over Int Phosphate in Powell 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 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 5,136 vehicles a day, roughly 22% of them trucks, projected to reach 5,469 by 2043. The structure is 128 ft (39 m) long and 45 ft wide.

Location

Open in Google Maps
CarriesI 90
CrossesInt Phosphate
Location3.7M W Garrison
RouteInterstate 90
CountyPowell County
StateMontana
Coordinates46.55657, -112.87021
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.
Substructure5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Last inspectionOctober 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourBridge not over waterway
Structural evaluation5: Somewhat better than minimum adequacy to tolerate being left in place as is
Deck geometry7: Better than present minimum criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating52 US tons
Inventory rating32 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialPrestressed Concrete
DeckConcrete, cast-in-place
Main spans3
Design loadHS 20
Structure length128 ft (39 m)
Longest span46 ft (14 m)
Deck width45 ft (13.7 m)
Roadway width42 ft (12.7 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic5,136 (2023)
Projected traffic5,469 by 2043
Trucks22%
Lanes on structure2
Traffic directionOne-way traffic
CarriesOverpass structure at an interchange
CrossesHighway
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—
NavigationNot applicable (no waterway)

Frequently asked questions

When was I 90 over Int Phosphate built?

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

What condition is I 90 over Int Phosphate 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 October 2023.

How much traffic does I 90 over Int Phosphate carry?

About 5,136 vehicles per day (2023 count), of which roughly 22% are trucks.

How long is I 90 over Int Phosphate?

The structure is 128 ft (39 m) long with a longest span of 46 ft (14 m) and a deck 45 ft wide.

Who owns I 90 over Int Phosphate?

It is owned by the State Highway Agency.