US Bridges

I 90 over Sep County Road

Fair

Sweet Grass County, Montana · 5M W Big Timber · Structure no. I00090363+05672

Built
1981
44 years old
Condition
Fair
inspected June 2023
Type
Slab
Concrete Continuous
Length
79 ft
3 main spans
Daily traffic
6,090
2023 count
Owner
State
State Highway Agency

About this bridge

I 90 over Sep County Road is a concrete continuous slab carrying I 90 over Sep County Road in Sweet Grass County, Montana. It was built in 1981, 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 6,090 vehicles a day, roughly 18% of them trucks, projected to reach 6,638 by 2043. The structure is 79 ft (24.1 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 90
CrossesSep County Road
Location5M W Big Timber
RouteInterstate 90
CountySweet Grass County
StateMontana
Coordinates45.79176, -110.04229
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.
Substructure5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Last inspectionJune 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 rating34 US tons
Inventory rating26 US tons

Structure

Structure typeSlab
MaterialConcrete Continuous
DeckConcrete, cast-in-place
Main spans3
Design loadHS 20
Structure length79 ft (24.1 m)
Longest span30 ft (9.1 m)
Deck width44 ft (13.5 m)
Roadway width41 ft (12.6 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic6,090 (2023)
Projected traffic6,638 by 2043
Trucks18%
Lanes on structure2
Traffic directionOne-way traffic
CarriesHighway
CrossesHighway
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—
NavigationNot applicable (no waterway)

Frequently asked questions

When was I 90 over Sep County Road built?

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

What condition is I 90 over Sep County Road 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 2023.

How much traffic does I 90 over Sep County Road carry?

About 6,090 vehicles per day (2023 count), of which roughly 18% are trucks.

How long is I 90 over Sep County Road?

The structure is 79 ft (24.1 m) long with a longest span of 30 ft (9.1 m) and a deck 44 ft wide.

Who owns I 90 over Sep County Road?

It is owned by the State Highway Agency.