US Bridges

IRR - S 313 over Bighorn River

Fair

Big Horn County, Montana · 7M SW Hardin · Structure no. S00313008+03271

Built
1958
67 years old
Condition
Fair
inspected July 2023
Type
Girder and Floorbeam System
Steel Continuous
Length
576 ft
4 main spans
Daily traffic
899
2023 count
Owner
State
State Highway Agency

About this bridge

IRR - S 313 over Bighorn River is a steel continuous girder and floorbeam system carrying IRR - S 313 over Bighorn River in Big Horn County, Montana. It was built in 1958, so it is 67 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 899 vehicles a day, roughly 17% of them trucks, projected to reach 944 by 2043. The structure is 576 ft (175.5 m) long and 27 ft wide. If it were closed, the detour would be 80.2 mi (129 km).

Location

Open in Google Maps
CarriesIRR - S 313
CrossesBighorn River
Location7M SW Hardin
RouteState Highway 313
CountyBig Horn County
StateMontana
Coordinates45.64409, -107.65773
Functional classRural Major Collector

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 protection6 SatisfactoryStructural elements show some minor deterioration.
Last inspectionJuly 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourCountermeasures installed to correct a previously existing problem
Structural evaluation6: Equal to present minimum criteria
Deck geometry4: Meets minimum tolerable limits to be left in place as is
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment7: Better than present minimum criteria
Operating rating45 US tons
Inventory rating27 US tons

Structure

Structure typeGirder and Floorbeam System
MaterialSteel Continuous
DeckConcrete, cast-in-place
Main spans4
Design loadHS 15
Structure length576 ft (175.5 m)
Longest span160 ft (48.8 m)
Deck width27 ft (8.2 m)
Roadway width24 ft (7.3 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic899 (2023)
Projected traffic944 by 2043
Trucks17%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed80.2 mi (129 km)
TollOn a free road
National Highway SystemNo

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—
NavigationNavigation control on waterway (bridge permit required)

Frequently asked questions

When was IRR - S 313 over Bighorn River built?

It was built in 1958, making it 67 years old in 2025.

What condition is IRR - S 313 over Bighorn 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 IRR - S 313 over Bighorn River carry?

About 899 vehicles per day (2023 count), of which roughly 17% are trucks.

How long is IRR - S 313 over Bighorn River?

The structure is 576 ft (175.5 m) long with a longest span of 160 ft (48.8 m) and a deck 27 ft wide.

Who owns IRR - S 313 over Bighorn River?

It is owned by the State Highway Agency.