US Bridges

Oak Knoll Ave over Napa River Overflow

FairPosted for load

Napa County, California · 300 W Silverado Trail · Structure no. 21C0104

Built
1910
115 years old
Condition
Fair
inspected May 2023
Type
Arch - Deck
Masonry
Length
20 ft
1 main span
Daily traffic
2,600
2005 count
Owner
County
County Highway Agency

About this bridge

Oak Knoll Ave over Napa River Overflow is a masonry arch - deck carrying Oak Knoll Ave over Napa River Overflow in Napa County, California. It was built in 1910, so it is 115 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. Its operating status is: posted for load restriction.

It carries about 2,600 vehicles a day, roughly 10% of them trucks, projected to reach 3,965 by 2040. The structure is 20 ft (6.2 m) long and 24 ft wide. If it were closed, the detour would be 6.2 mi (10 km).

Location

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CarriesOak Knoll Ave
CrossesNapa River Overflow
Location300 W Silverado Trail
RouteCounty Highway 0
CountyNapa County
StateCalifornia
Coordinates38.36913, -122.30211
Functional classRural 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
Deck7 GoodSome minor problems.
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 inspectionMay 2023
Inspection intervalevery 24 months
Operating statusPosted for load restriction
ScourFoundations stable; scour above top of footing
Structural evaluation4: Meets minimum tolerable limits to be 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 rating30 US tons
Inventory rating17.9 US tons

Structure

Structure typeArch - Deck
MaterialMasonry
DeckConcrete, cast-in-place
Main spans1
Design loadUnknown
Structure length20 ft (6.2 m)
Longest span20 ft (6.2 m)
Deck width24 ft (7.2 m)
Roadway width23 ft (7 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic2,600 (2005)
Projected traffic3,965 by 2040
Trucks10%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed6.2 mi (10 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 Oak Knoll Ave over Napa River Overflow built?

It was built in 1910, making it 115 years old in 2025.

What condition is Oak Knoll Ave over Napa River Overflow 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 Oak Knoll Ave over Napa River Overflow carry?

About 2,600 vehicles per day (2005 count), of which roughly 10% are trucks.

How long is Oak Knoll Ave over Napa River Overflow?

The structure is 20 ft (6.2 m) long with a longest span of 20 ft (6.2 m) and a deck 24 ft wide.

Who owns Oak Knoll Ave over Napa River Overflow?

It is owned by the County Highway Agency.