US Bridges

Forest Road 421 over Mallard Creek

Fair

Idaho County, Idaho · No Data Entered · Structure no. 011705000000079

Built
1992
33 years old
Condition
Fair
inspected August 2022
Type
Stringer/Multi-beam or Girder
Wood or Timber
Length
32 ft
1 main span
Daily traffic
50
Owner
Federal
U.S. Forest Service

About this bridge

Forest Road 421 over Mallard Creek is a wood or timber stringer/multi-beam or girder carrying Forest Road 421 over Mallard Creek in Idaho County, Idaho. It was built in 1992, so it is 33 years old, younger 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 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 32 ft (9.9 m) long and 16 ft wide. If it were closed, the detour would be 98.2 mi (158 km).

Location

Open in Google Maps
CarriesForest Road 421
CrossesMallard Creek
LocationNo Data Entered
RouteFederal Lands Road 421
CountyIdaho County
StateIdaho
Coordinates45.61463, -115.31881
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.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Channel and channel protection6 SatisfactoryStructural elements show some minor deterioration.
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 adequacy8: Equal to present desirable criteria
Approach roadway alignment6: Equal to present minimum criteria
Operating rating25.4 US tons
Inventory rating19.3 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialWood or Timber
DeckWood or timber
Main spans1
Design loadHS 20
Structure length32 ft (9.9 m)
Longest span31 ft (9.6 m)
Deck width16 ft (4.9 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 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 421 over Mallard Creek built?

It was built in 1992, making it 33 years old in 2025.

What condition is Forest Road 421 over Mallard 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 421 over Mallard Creek carry?

About 50 vehicles per day (latest count).

How long is Forest Road 421 over Mallard Creek?

The structure is 32 ft (9.9 m) long with a longest span of 31 ft (9.6 m) and a deck 16 ft wide.

Who owns Forest Road 421 over Mallard Creek?

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