US Bridges

Dunbar RD over Calabazas Creek

Fair

Sonoma County, California · 0.1 MI N Sylvia Drive · Structure no. 20C0271

Built
1915
110 years old, rebuilt 1940
Condition
Fair
inspected May 2023
Type
Arch - Deck
Masonry
Length
25 ft
1 main span
Daily traffic
800
2015 count
Owner
County
County Highway Agency

About this bridge

Dunbar RD over Calabazas Creek is a masonry arch - deck carrying Dunbar RD over Calabazas Creek in Sonoma County, California. It was built in 1915 and reconstructed in 1940, so it is 110 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 800 vehicles a day, roughly 5% of them trucks, projected to reach 915 by 2040. The structure is 25 ft (7.6 m) long and 28 ft wide. If it were closed, the detour would be 3.1 mi (5 km).

Location

Open in Google Maps
CarriesDunbar RD
CrossesCalabazas Creek
Location0.1 MI N Sylvia Drive
RouteCounty Highway 0
CountySonoma County
StateCalifornia
Coordinates38.38325, -122.52127
Functional classUrban 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.
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 statusOpen, no restriction
ScourFoundations stable; scour above top of footing
Structural evaluation4: Meets minimum tolerable limits to be left in place as is
Deck geometry4: Meets minimum tolerable limits to be left in place as is
Waterway adequacy7: Better than present minimum criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating31.7 US tons
Inventory rating19 US tons

Structure

Structure typeArch - Deck
MaterialMasonry
DeckConcrete, cast-in-place
Main spans1
Design loadUnknown
Structure length25 ft (7.6 m)
Longest span23 ft (7 m)
Deck width28 ft (8.4 m)
Roadway width24 ft (7.2 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic800 (2015)
Projected traffic915 by 2040
Trucks5%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed3.1 mi (5 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 Dunbar RD over Calabazas Creek built?

It was built in 1915, making it 110 years old in 2025. It was reconstructed in 1940.

What condition is Dunbar RD over Calabazas 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 May 2023.

How much traffic does Dunbar RD over Calabazas Creek carry?

About 800 vehicles per day (2015 count), of which roughly 5% are trucks.

How long is Dunbar RD over Calabazas Creek?

The structure is 25 ft (7.6 m) long with a longest span of 23 ft (7 m) and a deck 28 ft wide.

Who owns Dunbar RD over Calabazas Creek?

It is owned by the County Highway Agency.