US Bridges

RD 4791 over Granite CR

Fair

Lincoln County, Montana · Lower Granite · Structure no. 011405000000072

Built
1964
61 years old
Condition
Fair
inspected August 2024
Type
Stringer/Multi-beam or Girder
Wood or Timber
Length
40 ft
1 main span
Daily traffic
50
Owner
Federal
U.S. Forest Service

About this bridge

RD 4791 over Granite CR is a wood or timber stringer/multi-beam or girder carrying RD 4791 over Granite CR in Lincoln County, Montana. It was built in 1964, so it is 61 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 50 vehicles a day, projected to reach 75 by 2045. The structure is 40 ft (12.3 m) long and 15 ft wide.

Location

Open in Google Maps
CarriesRD 4791
CrossesGranite CR
LocationLower Granite
RouteFederal Lands Road 4791
CountyLincoln County
StateMontana
Coordinates48.30865, -115.54141
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.
Superstructure7 GoodSome minor problems.
Substructure5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Channel and channel protection4 PoorAdvanced section loss, deterioration, spalling or scour.
Last inspectionAugust 2024
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 geometry5: Somewhat better than minimum adequacy to tolerate being left in place as is
Waterway adequacy7: Better than present minimum criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating30.8 US tons
Inventory rating23.9 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialWood or Timber
DeckWood or timber
Main spans1
Design loadUnknown
Structure length40 ft (12.3 m)
Longest span39 ft (11.9 m)
Deck width15 ft (4.7 m)
Roadway width13 ft (4.1 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 4791 over Granite CR built?

It was built in 1964, making it 61 years old in 2025.

What condition is RD 4791 over Granite CR 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 August 2024.

How much traffic does RD 4791 over Granite CR carry?

About 50 vehicles per day (latest count).

How long is RD 4791 over Granite CR?

The structure is 40 ft (12.3 m) long with a longest span of 39 ft (11.9 m) and a deck 15 ft wide.

Who owns RD 4791 over Granite CR?

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