US Bridges

State Route 299 over Mad River

Good

Humboldt County, California · 01-HUM-299-R1.55 · Structure no. 04 0036R

Built
1948
77 years old, rebuilt 2003
Condition
Good
inspected November 2023
Type
Stringer/Multi-beam or Girder
Steel Continuous
Length
517 ft
2 main spans
Daily traffic
4,775
2010 count
Owner
State
State Highway Agency

About this bridge

State Route 299 over Mad River is a steel continuous stringer/multi-beam or girder carrying State Route 299 over Mad River in Humboldt County, California. It was built in 1948 and reconstructed in 2003, so it is 77 years old, older than the California average of 54.8 years.

The most recent inspection reported to the Federal Highway Administration rates it in good condition with a lowest component rating of 7 out of 9. All primary components (deck, superstructure, substructure, or culvert) are rated 7 or higher. No significant problems were noted.

It carries about 4,775 vehicles a day, roughly 14% of them trucks, projected to reach 5,469 by 2041. The structure is 517 ft (157.7 m) long and 41 ft wide. If it were closed, the detour would be 1.2 mi (2 km).

Location

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CarriesState Route 299
CrossesMad River
Location01-HUM-299-R1.55
RouteState Highway 299
CountyHumboldt County
StateCalifornia
Coordinates40.91019, -124.06261
Functional classRural Principal Arterial - Other

Condition and inspection

Good

All primary components (deck, superstructure, substructure, or culvert) are rated 7 or higher. No significant problems were noted.

ComponentRatingMeaning
Deck7 GoodSome minor problems.
Superstructure7 GoodSome minor problems.
Substructure7 GoodSome minor problems.
Channel and channel protection7 GoodSome minor problems.
Last inspectionNovember 2023
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 geometry7: Better than present minimum criteria
Waterway adequacy6: Equal to present minimum criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating26.8 US tons
Inventory rating20.7 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialSteel Continuous
DeckConcrete, cast-in-place
Main spans2 (+4 approach)
Design loadHS 15
Structure length517 ft (157.7 m)
Longest span150 ft (45.7 m)
Deck width41 ft (12.6 m)
Roadway width38 ft (11.7 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic4,775 (2010)
Projected traffic5,469 by 2041
Trucks14%
Lanes on structure2
Traffic directionOne-way traffic
CarriesHighway
CrossesHighway and waterway
Detour if closed1.2 mi (2 km)
TollOn a free road
National Highway SystemYes
Strategic Highway NetworkInterstate STRAHNET route

Ownership and planned work

OwnerState Highway Agency
Maintained byState 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 State Route 299 over Mad River built?

It was built in 1948, making it 77 years old in 2025. It was reconstructed in 2003.

What condition is State Route 299 over Mad River in?

The National Bridge Inventory rates it in good condition. All primary components (deck, superstructure, substructure, or culvert) are rated 7 or higher. No significant problems were noted. The last reported inspection was in November 2023.

How much traffic does State Route 299 over Mad River carry?

About 4,775 vehicles per day (2010 count), of which roughly 14% are trucks.

How long is State Route 299 over Mad River?

The structure is 517 ft (157.7 m) long with a longest span of 150 ft (45.7 m) and a deck 41 ft wide.

Who owns State Route 299 over Mad River?

It is owned by the State Highway Agency.