US Bridges

Watmaugh Road over Sonoma Creek

FairPosted for load

Sonoma County, California · 0.3 MI West of SR 12 · Structure no. 20C0017

Built
1929
96 years old
Condition
Fair
inspected April 2024
Type
Truss - Thru
Steel
Length
170 ft
1 main span
Daily traffic
3,628
2016 count
Owner
County
County Highway Agency

About this bridge

Watmaugh Road over Sonoma Creek is a steel truss - thru carrying Watmaugh Road over Sonoma Creek in Sonoma County, California. It was built in 1929, so it is 96 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 3,628 vehicles a day, roughly 1% of them trucks, projected to reach 2,137 by 2046. The structure is 170 ft (51.8 m) long and 24 ft wide. If it were closed, the detour would be 5 mi (8 km).

Location

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CarriesWatmaugh Road
CrossesSonoma Creek
Location0.3 MI West of SR 12
RouteCounty Highway 0
CountySonoma County
StateCalifornia
Coordinates38.26569, -122.46757
Functional classUrban Collector

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.
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 inspectionApril 2024
Inspection intervalevery 12 months
Operating statusPosted for load restriction
ScourScour critical; foundations unstable for calculated scour conditions
Structural evaluation4: Meets minimum tolerable limits to be left in place as is
Deck geometry2: Basically intolerable, requiring high priority of replacement
Waterway adequacy6: Equal to present minimum criteria
Approach roadway alignment3: Basically intolerable, requiring high priority of corrective action
Operating rating24.3 US tons
Inventory rating14.7 US tons

Structure

Structure typeTruss - Thru
MaterialSteel
DeckConcrete, cast-in-place
Main spans1 (+2 approach)
Design loadH 15
Structure length170 ft (51.8 m)
Longest span103 ft (31.4 m)
Deck width24 ft (7.2 m)
Roadway width22 ft (6.8 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic3,628 (2016)
Projected traffic2,137 by 2046
Trucks1%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed5 mi (8 km)
TollOn a free road
National Highway SystemNo

Ownership and planned work

OwnerCounty Highway Agency
Maintained byCounty Highway Agency
Historic statusEligible for the National Register of Historic Places
Work proposedNone recorded
Estimated improvement cost—
NavigationNo navigation control on waterway

Frequently asked questions

When was Watmaugh Road over Sonoma Creek built?

It was built in 1929, making it 96 years old in 2025.

What condition is Watmaugh Road over Sonoma 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 April 2024.

How much traffic does Watmaugh Road over Sonoma Creek carry?

About 3,628 vehicles per day (2016 count), of which roughly 1% are trucks.

How long is Watmaugh Road over Sonoma Creek?

The structure is 170 ft (51.8 m) long with a longest span of 103 ft (31.4 m) and a deck 24 ft wide.

Who owns Watmaugh Road over Sonoma Creek?

It is owned by the County Highway Agency.