US Bridges

US 12 over Missouri River

Fair

Broadwater County, Montana · 1M N Townsend · Structure no. P00008076+03431

Built
1935
90 years old, rebuilt 1986
Condition
Fair
inspected May 2023
Type
Stringer/Multi-beam or Girder
Steel Continuous
Length
500 ft
5 main spans
Daily traffic
6,843
2023 count
Owner
State
State Highway Agency

About this bridge

US 12 over Missouri River is a steel continuous stringer/multi-beam or girder carrying US 12 over Missouri River in Broadwater County, Montana. It was built in 1935 and reconstructed in 1986, so it is 90 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 6,843 vehicles a day, roughly 4% of them trucks, projected to reach 7,493 by 2043. The structure is 500 ft (152.4 m) long and 51 ft wide. If it were closed, the detour would be 80.2 mi (129 km).

Location

Open in Google Maps
CarriesUS 12
CrossesMissouri River
Location1M N Townsend
RouteU.S. Route 12
CountyBroadwater County
StateMontana
Coordinates46.33518, -111.53173
Functional classRural Principal Arterial - Other

Condition and inspection

Fair

The lowest-rated primary component is rated 5 or 6. Minor deterioration is present but the structure is sound.

ComponentRatingMeaning
Deck5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
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 inspectionMay 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 rating46 US tons
Inventory rating27 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialSteel Continuous
DeckConcrete, cast-in-place
Main spans5
Design loadHS 20
Structure length500 ft (152.4 m)
Longest span107 ft (32.6 m)
Deck width51 ft (15.5 m)
Roadway width48 ft (14.5 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic6,843 (2023)
Projected traffic7,493 by 2043
Trucks4%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed80.2 mi (129 km)
TollOn a free road
National Highway SystemYes

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 US 12 over Missouri River built?

It was built in 1935, making it 90 years old in 2025. It was reconstructed in 1986.

What condition is US 12 over Missouri 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 May 2023.

How much traffic does US 12 over Missouri River carry?

About 6,843 vehicles per day (2023 count), of which roughly 4% are trucks.

How long is US 12 over Missouri River?

The structure is 500 ft (152.4 m) long with a longest span of 107 ft (32.6 m) and a deck 51 ft wide.

Who owns US 12 over Missouri River?

It is owned by the State Highway Agency.