US Bridges

State Route 121 over Sonoma Creek

Fair

Sonoma County, California · 04-SON-121-R7.30 · Structure no. 20 0022

Built
1971
54 years old
Condition
Fair
inspected November 2024
Type
Box Beam or Girders - Multiple
Concrete Continuous
Length
231 ft
3 main spans
Daily traffic
19,000
2014 count
Owner
State
State Highway Agency

About this bridge

State Route 121 over Sonoma Creek is a concrete continuous box beam or girders - multiple carrying State Route 121 over Sonoma Creek in Sonoma County, California. It was built in 1971, so it is 54 years old, younger 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 6 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 19,000 vehicles a day, roughly 7% of them trucks, projected to reach 27,636 by 2046. The structure is 231 ft (70.4 m) long and 47 ft wide. If it were closed, the detour would be 6.8 mi (11 km).

Location

Open in Google Maps
CarriesState Route 121
CrossesSonoma Creek
Location04-SON-121-R7.30
RouteState Highway 121
CountySonoma County
StateCalifornia
Coordinates38.24037, -122.45142
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
Deck6 SatisfactoryStructural elements show some minor deterioration.
Superstructure7 GoodSome minor problems.
Substructure8 Very GoodNo problems noted.
Channel and channel protection7 GoodSome minor problems.
Last inspectionNovember 2024
Inspection intervalevery 48 months
Operating statusOpen, no restriction
ScourFoundations stable; scour above top of footing
Structural evaluation7: Better than present minimum criteria
Deck geometry5: Somewhat better than minimum adequacy to tolerate being left in place as is
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating53.6 US tons
Inventory rating41.1 US tons

Structure

Structure typeBox Beam or Girders - Multiple
MaterialConcrete Continuous
DeckConcrete, cast-in-place
Main spans3
Design loadHS 20
Structure length231 ft (70.4 m)
Longest span100 ft (30.5 m)
Deck width47 ft (14.3 m)
Roadway width40 ft (12.2 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic19,000 (2014)
Projected traffic27,636 by 2046
Trucks7%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway and pedestrian
CrossesWaterway
Detour if closed6.8 mi (11 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—
NavigationNo navigation control on waterway

Frequently asked questions

When was State Route 121 over Sonoma Creek built?

It was built in 1971, making it 54 years old in 2025.

What condition is State Route 121 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 November 2024.

How much traffic does State Route 121 over Sonoma Creek carry?

About 19,000 vehicles per day (2014 count), of which roughly 7% are trucks.

How long is State Route 121 over Sonoma Creek?

The structure is 231 ft (70.4 m) long with a longest span of 100 ft (30.5 m) and a deck 47 ft wide.

Who owns State Route 121 over Sonoma Creek?

It is owned by the State Highway Agency.