US Bridges

Old Darby RD over Rock Creek 052

FairPosted for load

Ravalli County, Montana · 4M N Darby · Structure no. L41703003+05001

Built
1918
107 years old, rebuilt 1936
Condition
Fair
inspected August 2023
Type
Stringer/Multi-beam or Girder
Steel
Length
61 ft
2 main spans
Daily traffic
100
2025 count
Owner
County
County Highway Agency

About this bridge

Old Darby RD over Rock Creek 052 is a steel stringer/multi-beam or girder carrying Old Darby RD over Rock Creek 052 in Ravalli County, Montana. It was built in 1918 and reconstructed in 1936, so it is 107 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. Its operating status is: posted for load restriction.

It carries about 100 vehicles a day, roughly 3% of them trucks, projected to reach 100 by 2040. The structure is 61 ft (18.6 m) long and 16 ft wide. If it were closed, the detour would be 5 mi (8 km).

Location

Open in Google Maps
CarriesOld Darby RD
CrossesRock Creek 052
Location4M N Darby
RouteCounty Highway 41703
CountyRavalli County
StateMontana
Coordinates46.08221, -114.17516
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
Deck5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Superstructure6 SatisfactoryStructural elements show some minor deterioration.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Channel and channel protection8 Very GoodNo problems noted.
Last inspectionAugust 2023
Inspection intervalevery 24 months
Operating statusPosted for load restriction
ScourFoundations stable; scour within limits of footing or piles
Structural evaluation6: Equal to present minimum criteria
Deck geometry7: Better than present minimum criteria
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment7: Better than present minimum criteria
Operating rating40.7 US tons
Inventory rating24.3 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialSteel
DeckConcrete, cast-in-place
Main spans2
Design loadHS 20
Structure length61 ft (18.6 m)
Longest span28 ft (8.5 m)
Deck width16 ft (4.9 m)
Roadway width15 ft (4.6 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic100 (2025)
Projected traffic100 by 2040
Trucks3%
Lanes on structure1
Traffic directionOne-lane bridge for two-way traffic
CarriesHighway
CrossesWaterway
Detour if closed5 mi (8 km)
TollOn a free road
National Highway SystemNo

Ownership and planned work

OwnerCounty Highway Agency
Maintained byCounty 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 Old Darby RD over Rock Creek 052 built?

It was built in 1918, making it 107 years old in 2025. It was reconstructed in 1936.

What condition is Old Darby RD over Rock Creek 052 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 2023.

How much traffic does Old Darby RD over Rock Creek 052 carry?

About 100 vehicles per day (2025 count), of which roughly 3% are trucks.

How long is Old Darby RD over Rock Creek 052?

The structure is 61 ft (18.6 m) long with a longest span of 28 ft (8.5 m) and a deck 16 ft wide.

Who owns Old Darby RD over Rock Creek 052?

It is owned by the County Highway Agency.