US Bridges

Mattole RD over Harper Creek

Fair

Humboldt County, California · 4.3 MI W/O HWY 101 · Structure no. 04P0007

Built
1977
48 years old
Condition
Fair
inspected March 2022
Type
Culvert
Concrete Continuous
Length
21 ft
2 main spans
Daily traffic
600
2009 count
Owner
State
State Park, Forest, or Reservation Agency

About this bridge

Mattole RD over Harper Creek is a concrete continuous culvert carrying Mattole RD over Harper Creek in Humboldt County, California. It was built in 1977, so it is 48 years old, younger 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 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 600 vehicles a day, roughly 10% of them trucks, projected to reach 1,599 by 2040. The structure is 21 ft (6.3 m) long and 22 ft wide. If it were closed, the detour would be 60.3 mi (97 km).

Location

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CarriesMattole RD
CrossesHarper Creek
Location4.3 MI W/O HWY 101
RouteState Lands Road 0
CountyHumboldt County
StateCalifornia
Coordinates40.3512, -123.98812
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
Channel and channel protection7 GoodSome minor problems.
Culvert6 SatisfactoryStructural elements show some minor deterioration.
Last inspectionMarch 2022
Inspection intervalevery 48 months
Operating statusOpen, no restriction
ScourFoundations stable; scour above top of footing
Structural evaluation6: Equal to present minimum criteria
Deck geometry2: Basically intolerable, requiring high priority of replacement
Waterway adequacy7: Better than present minimum criteria
Approach roadway alignment6: Equal to present minimum criteria
Operating rating59.6 US tons
Inventory rating35.7 US tons

Structure

Structure typeCulvert
MaterialConcrete Continuous
DeckConcrete, cast-in-place
Main spans2
Design loadUnknown
Structure length21 ft (6.3 m)
Longest span11 ft (3.4 m)
Deck width22 ft (6.7 m)
Roadway width20 ft (6 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic600 (2009)
Projected traffic1,599 by 2040
Trucks10%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed60.3 mi (97 km)
TollOn a free road
National Highway SystemNo

Ownership and planned work

OwnerState Park, Forest, or Reservation Agency
Maintained byState Park, Forest, or Reservation Agency
Historic statusHistorical significance not determinable at this time
Work proposedNone recorded
Estimated improvement cost—
NavigationNo navigation control on waterway

Frequently asked questions

When was Mattole RD over Harper Creek built?

It was built in 1977, making it 48 years old in 2025.

What condition is Mattole RD over Harper 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 March 2022.

How much traffic does Mattole RD over Harper Creek carry?

About 600 vehicles per day (2009 count), of which roughly 10% are trucks.

How long is Mattole RD over Harper Creek?

The structure is 21 ft (6.3 m) long with a longest span of 11 ft (3.4 m) and a deck 22 ft wide.

Who owns Mattole RD over Harper Creek?

It is owned by the State Park, Forest, or Reservation Agency.