US Bridges

Forest Road 309 over Mill Creek

Fair

Idaho County, Idaho · 2.7 Mi. from State HWY 14 · Structure no. 011704000000047

Built
1966
59 years old, rebuilt 1991
Condition
Fair
inspected August 2022
Type
Stringer/Multi-beam or Girder
Wood or Timber
Length
35 ft
1 main span
Daily traffic
30
Owner
Federal
U.S. Forest Service

About this bridge

Forest Road 309 over Mill Creek is a wood or timber stringer/multi-beam or girder carrying Forest Road 309 over Mill Creek in Idaho County, Idaho. It was built in 1966 and reconstructed in 1991, so it is 59 years old, older than the Idaho average of 45.3 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 30 vehicles a day, projected to reach 45 by 2045. The structure is 35 ft (10.8 m) long and 15 ft wide. If it were closed, the detour would be 98.2 mi (158 km).

Location

Open in Google Maps
CarriesForest Road 309
CrossesMill Creek
Location2.7 Mi. from State HWY 14
RouteFederal Lands Road 309
CountyIdaho County
StateIdaho
Coordinates45.79759, -115.958
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
Deck6 SatisfactoryStructural elements show some minor deterioration.
Superstructure7 GoodSome minor problems.
Substructure5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Channel and channel protection7 GoodSome minor problems.
Last inspectionAugust 2022
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 geometry6: Equal to present minimum criteria
Waterway adequacy9: Superior to present desirable criteria
Approach roadway alignment6: Equal to present minimum criteria
Operating rating36.4 US tons
Inventory rating28.2 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialWood or Timber
DeckWood or timber
Main spans1
Design loadHS 20
Structure length35 ft (10.8 m)
Longest span34 ft (10.5 m)
Deck width15 ft (4.7 m)
Roadway width14 ft (4.4 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic30 (—)
Projected traffic45 by 2045
Trucks—
Lanes on structure1
Traffic directionOne-lane bridge for two-way traffic
CarriesHighway
CrossesWaterway
Detour if closed98.2 mi (158 km)
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 Forest Road 309 over Mill Creek built?

It was built in 1966, making it 59 years old in 2025. It was reconstructed in 1991.

What condition is Forest Road 309 over Mill Creek 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 2022.

How much traffic does Forest Road 309 over Mill Creek carry?

About 30 vehicles per day (latest count).

How long is Forest Road 309 over Mill Creek?

The structure is 35 ft (10.8 m) long with a longest span of 34 ft (10.5 m) and a deck 15 ft wide.

Who owns Forest Road 309 over Mill Creek?

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