US Bridges

Adobe Canyon Road over Hillside

Fair

Sonoma County, California · 1.1 MI Nw/O SR 12 · Structure no. 20C0404

Built
1965
60 years old
Condition
Fair
inspected May 2023
Type
Slab
Concrete
Length
108 ft
1 main span
Daily traffic
650
2015 count
Owner
County
County Highway Agency

About this bridge

Adobe Canyon Road over Hillside is a concrete slab carrying Adobe Canyon Road over Hillside in Sonoma County, California. It was built in 1965, so it is 60 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 650 vehicles a day, roughly 5% of them trucks, projected to reach 1,118 by 2040. The structure is 108 ft (33 m) long and 9 ft wide. If it were closed, the detour would be 61.5 mi (99 km).

Location

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CarriesAdobe Canyon Road
CrossesHillside
Location1.1 MI Nw/O SR 12
RouteCounty Highway 0
CountySonoma County
StateCalifornia
Coordinates38.43706, -122.54667
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.
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 inspectionMay 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourScour critical; foundations unstable for calculated scour conditions
Structural evaluation5: Somewhat better than minimum adequacy to tolerate being left in place as is
Deck geometry2: Basically intolerable, requiring high priority of replacement
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating44.6 US tons
Inventory rating26.8 US tons

Structure

Structure typeSlab
MaterialConcrete
DeckConcrete, cast-in-place
Main spans1
Design loadUnknown
Structure length108 ft (33 m)
Longest span3 ft (0.9 m)
Deck width9 ft (2.8 m)
Roadway width18 ft (5.5 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic650 (2015)
Projected traffic1,118 by 2040
Trucks5%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed61.5 mi (99 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—
NavigationNot applicable (no waterway)

Frequently asked questions

When was Adobe Canyon Road over Hillside built?

It was built in 1965, making it 60 years old in 2025.

What condition is Adobe Canyon Road over Hillside 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 May 2023.

How much traffic does Adobe Canyon Road over Hillside carry?

About 650 vehicles per day (2015 count), of which roughly 5% are trucks.

How long is Adobe Canyon Road over Hillside?

The structure is 108 ft (33 m) long with a longest span of 3 ft (0.9 m) and a deck 9 ft wide.

Who owns Adobe Canyon Road over Hillside?

It is owned by the County Highway Agency.