US Bridges

Twelfth ST over U.S. Highway 101

Fair

Humboldt County, California · 01-HUM-101-60.49 · Structure no. 04 0130

Built
1962
63 years old
Condition
Fair
inspected August 2023
Type
Tee Beam
Concrete Continuous
Length
197 ft
4 main spans
Daily traffic
2,500
2010 count
Owner
State
State Highway Agency

About this bridge

Twelfth ST over U.S. Highway 101 is a concrete continuous tee beam carrying Twelfth ST over U.S. Highway 101 in Humboldt County, California. It was built in 1962, so it is 63 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 2,500 vehicles a day, roughly 10% of them trucks, projected to reach 1,664 by 2043. The structure is 197 ft (60 m) long and 34 ft wide. If it were closed, the detour would be 3.1 mi (5 km).

Location

Open in Google Maps
CarriesTwelfth ST
CrossesU.S. Highway 101
Location01-HUM-101-60.49
RouteCounty Highway 0
CountyHumboldt County
StateCalifornia
Coordinates40.58764, -124.15542
Functional classUrban Minor Arterial

Condition and inspection

Fair

The lowest-rated primary component is rated 5 or 6. Minor deterioration is present but the structure is sound.

ComponentRatingMeaning
Deck5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Superstructure5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Substructure7 GoodSome minor problems.
Last inspectionAugust 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourBridge not over waterway
Structural evaluation5: Somewhat better than minimum adequacy to tolerate being left in place as is
Deck geometry4: Meets minimum tolerable limits to be left in place as is
Approach roadway alignment8: Equal to present desirable criteria
Operating rating47.5 US tons
Inventory rating36.8 US tons

Structure

Structure typeTee Beam
MaterialConcrete Continuous
DeckConcrete, cast-in-place
Main spans4
Design loadHS 20
Structure length197 ft (60 m)
Longest span65 ft (19.9 m)
Deck width34 ft (10.4 m)
Roadway width28 ft (8.5 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic2,500 (2010)
Projected traffic1,664 by 2043
Trucks10%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesHighway
Detour if closed3.1 mi (5 km)
TollOn a free road
National Highway SystemNo

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—
NavigationNot applicable (no waterway)

Frequently asked questions

When was Twelfth ST over U.S. Highway 101 built?

It was built in 1962, making it 63 years old in 2025.

What condition is Twelfth ST over U.S. Highway 101 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 2023.

How much traffic does Twelfth ST over U.S. Highway 101 carry?

About 2,500 vehicles per day (2010 count), of which roughly 10% are trucks.

How long is Twelfth ST over U.S. Highway 101?

The structure is 197 ft (60 m) long with a longest span of 65 ft (19.9 m) and a deck 34 ft wide.

Who owns Twelfth ST over U.S. Highway 101?

It is owned by the State Highway Agency.