US Bridges

RD 431 over ST Regis River

Fair

Mineral County, Montana · Twomile CR · Structure no. 011607000000086

Built
1957
68 years old
Condition
Fair
inspected May 2023
Type
Stringer/Multi-beam or Girder
Steel
Length
151 ft
3 main spans
Daily traffic
50
Owner
Federal
U.S. Forest Service

About this bridge

RD 431 over ST Regis River is a steel stringer/multi-beam or girder carrying RD 431 over ST Regis River in Mineral County, Montana. It was built in 1957, so it is 68 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 50 vehicles a day, projected to reach 75 by 2045. The structure is 151 ft (46 m) long and 18 ft wide.

Location

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CarriesRD 431
CrossesST Regis River
LocationTwomile CR
RouteFederal Lands Road 431
CountyMineral County
StateMontana
Coordinates47.29557, -115.16934
Functional classRural Local

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.
Superstructure6 SatisfactoryStructural elements show some minor deterioration.
Substructure7 GoodSome minor problems.
Channel and channel protection7 GoodSome minor problems.
Last inspectionMay 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour within limits of footing or piles
Structural evaluation6: Equal to present minimum criteria
Deck geometry6: Equal to present minimum criteria
Waterway adequacy9: Superior to present desirable criteria
Approach roadway alignment7: Better than present minimum criteria
Operating rating35.1 US tons
Inventory rating27.1 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialSteel
DeckConcrete, cast-in-place
Main spans3 (+2 approach)
Design loadHS 20
Structure length151 ft (46 m)
Longest span94 ft (28.7 m)
Deck width18 ft (5.5 m)
Roadway width14 ft (4.3 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic50 (—)
Projected traffic75 by 2045
Trucks—
Lanes on structure1
Traffic directionOne-lane bridge for two-way traffic
CarriesHighway
CrossesWaterway
Detour if closed—
TollOn a free road
National Highway SystemNo

Ownership and planned work

OwnerU.S. Forest Service
Maintained byU.S. Forest Service
Historic statusHistorical significance not determinable at this time
Work proposedNone recorded
Estimated improvement cost—
NavigationNo navigation control on waterway

Frequently asked questions

When was RD 431 over ST Regis River built?

It was built in 1957, making it 68 years old in 2025.

What condition is RD 431 over ST Regis 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 RD 431 over ST Regis River carry?

About 50 vehicles per day (latest count).

How long is RD 431 over ST Regis River?

The structure is 151 ft (46 m) long with a longest span of 94 ft (28.7 m) and a deck 18 ft wide.

Who owns RD 431 over ST Regis River?

It is owned by the U.S. Forest Service.