US Bridges

S 324 over Int Horse Prairie I 15

Fair

Beaverhead County, Montana · 1M E Clark Canyon Dam · Structure no. S00324000+00011

Built
1962
63 years old, rebuilt 1979
Condition
Fair
inspected January 2025
Type
Stringer/Multi-beam or Girder
Prestressed Concrete
Length
235 ft
4 main spans
Daily traffic
396
2023 count
Owner
State
State Highway Agency

About this bridge

S 324 over Int Horse Prairie I 15 is a prestressed concrete stringer/multi-beam or girder carrying S 324 over Int Horse Prairie I 15 in Beaverhead County, Montana. It was built in 1962 and reconstructed in 1979, so it is 63 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 396 vehicles a day, roughly 1% of them trucks, projected to reach 416 by 2043. The structure is 235 ft (71.6 m) long and 27 ft wide. If it were closed, the detour would be 14.3 mi (23 km).

Location

Open in Google Maps
CarriesS 324
CrossesInt Horse Prairie I 15
Location1M E Clark Canyon Dam
RouteState Highway 324
CountyBeaverhead County
StateMontana
Coordinates44.99894, -112.85373
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
Deck7 GoodSome minor problems.
Superstructure7 GoodSome minor problems.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Last inspectionJanuary 2025
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourBridge not over waterway
Structural evaluation4: Meets minimum tolerable limits to be left in place as is
Deck geometry5: Somewhat better than minimum adequacy to tolerate being left in place as is
Approach roadway alignment6: Equal to present minimum criteria
Operating rating41 US tons
Inventory rating15 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialPrestressed Concrete
DeckConcrete, cast-in-place
Main spans4
Design loadHS 15
Structure length235 ft (71.6 m)
Longest span76 ft (23.3 m)
Deck width27 ft (8.2 m)
Roadway width24 ft (7.3 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic396 (2023)
Projected traffic416 by 2043
Trucks1%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesOverpass structure at an interchange
CrossesHighway
Detour if closed14.3 mi (23 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 proposedReplacement because of substandard load-carrying capacity or roadway geometry
Estimated improvement cost$563,000
NavigationNot applicable (no waterway)

Frequently asked questions

When was S 324 over Int Horse Prairie I 15 built?

It was built in 1962, making it 63 years old in 2025. It was reconstructed in 1979.

What condition is S 324 over Int Horse Prairie I 15 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 January 2025.

How much traffic does S 324 over Int Horse Prairie I 15 carry?

About 396 vehicles per day (2023 count), of which roughly 1% are trucks.

How long is S 324 over Int Horse Prairie I 15?

The structure is 235 ft (71.6 m) long with a longest span of 76 ft (23.3 m) and a deck 27 ft wide.

Who owns S 324 over Int Horse Prairie I 15?

It is owned by the State Highway Agency.