US Bridges

RD 56 over W F Thompson Riv

Fair

Sanders County, Montana · Thompson River · Structure no. 011605000000009

Built
1935
90 years old
Condition
Fair
inspected October 2023
Type
Girder and Floorbeam System
Steel
Length
78 ft
1 main span
Daily traffic
50
Owner
Federal
U.S. Forest Service

About this bridge

RD 56 over W F Thompson Riv is a steel girder and floorbeam system carrying RD 56 over W F Thompson Riv in Sanders County, Montana. It was built in 1935, 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 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 78 ft (23.8 m) long and 19 ft wide. If it were closed, the detour would be 9.9 mi (16 km).

Location

Open in Google Maps
CarriesRD 56
CrossesW F Thompson Riv
LocationThompson River
RouteFederal Lands Road 56
CountySanders County
StateMontana
Coordinates47.64237, -115.17689
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 inspectionOctober 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; action required to protect exposed foundations
Structural evaluation5: Somewhat better than minimum adequacy to tolerate being left in place as is
Deck geometry4: Meets minimum tolerable limits to be left in place as is
Waterway adequacy9: Superior to present desirable criteria
Approach roadway alignment6: Equal to present minimum criteria
Operating rating28.2 US tons
Inventory rating21.8 US tons

Structure

Structure typeGirder and Floorbeam System
MaterialSteel
DeckWood or timber
Main spans1 (+2 approach)
Design loadH 15
Structure length78 ft (23.8 m)
Longest span45 ft (13.7 m)
Deck width19 ft (5.9 m)
Roadway width18 ft (5.5 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 closed9.9 mi (16 km)
TollOn a free road
National Highway SystemNo

Ownership and planned work

OwnerU.S. Forest Service
Maintained byCounty Highway Agency
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 56 over W F Thompson Riv built?

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

What condition is RD 56 over W F Thompson Riv 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 October 2023.

How much traffic does RD 56 over W F Thompson Riv carry?

About 50 vehicles per day (latest count).

How long is RD 56 over W F Thompson Riv?

The structure is 78 ft (23.8 m) long with a longest span of 45 ft (13.7 m) and a deck 19 ft wide.

Who owns RD 56 over W F Thompson Riv?

It is owned by the U.S. Forest Service and maintained by the County Highway Agency.