US Bridges

Mattole Road over Singley Creek

Fair

Humboldt County, California · 26.3 MI North of Honeydew · Structure no. 04C0147

Built
1959
66 years old
Condition
Fair
inspected August 2024
Type
Slab
Concrete Continuous
Length
123 ft
3 main spans
Daily traffic
308
2014 count
Owner
County
County Highway Agency

About this bridge

Mattole Road over Singley Creek is a concrete continuous slab carrying Mattole Road over Singley Creek in Humboldt County, California. It was built in 1959, so it is 66 years old, older than the California average of 54.8 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 308 vehicles a day, roughly 5% of them trucks, projected to reach 655 by 2044. The structure is 123 ft (37.5 m) long and 29 ft wide. If it were closed, the detour would be 95.7 mi (154 km).

Location

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CarriesMattole Road
CrossesSingley Creek
Location26.3 MI North of Honeydew
RouteCounty Highway 0
CountyHumboldt County
StateCalifornia
Coordinates40.43155, -124.40036
Functional classRural Major Collector

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.
Superstructure5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Substructure5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Channel and channel protection6 SatisfactoryStructural elements show some minor deterioration.
Last inspectionAugust 2024
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour within limits of footing or piles
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 rating84.3 US tons
Inventory rating50.4 US tons

Structure

Structure typeSlab
MaterialConcrete Continuous
DeckConcrete, cast-in-place
Main spans3
Design loadH 20
Structure length123 ft (37.5 m)
Longest span48 ft (14.6 m)
Deck width29 ft (8.7 m)
Roadway width28 ft (8.5 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic308 (2014)
Projected traffic655 by 2044
Trucks5%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed95.7 mi (154 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 Mattole Road over Singley Creek built?

It was built in 1959, making it 66 years old in 2025.

What condition is Mattole Road over Singley 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 2024.

How much traffic does Mattole Road over Singley Creek carry?

About 308 vehicles per day (2014 count), of which roughly 5% are trucks.

How long is Mattole Road over Singley Creek?

The structure is 123 ft (37.5 m) long with a longest span of 48 ft (14.6 m) and a deck 29 ft wide.

Who owns Mattole Road over Singley Creek?

It is owned by the County Highway Agency.