US Bridges

Swtwater Spring RD over Porter Creek

Fair

Sonoma County, California · 6.1 MI W Armstrong RD · Structure no. 20C0366

Built
1974
51 years old
Condition
Fair
inspected July 2023
Type
Stringer/Multi-beam or Girder
Steel Continuous
Length
40 ft
3 main spans
Daily traffic
140
2015 count
Owner
County
County Highway Agency

About this bridge

Swtwater Spring RD over Porter Creek is a steel continuous stringer/multi-beam or girder carrying Swtwater Spring RD over Porter Creek in Sonoma County, California. It was built in 1974, so it is 51 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 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 140 vehicles a day, roughly 1% of them trucks, projected to reach 105 by 2040. The structure is 40 ft (12.2 m) long and 14 ft wide. If it were closed, the detour would be 21.1 mi (34 km).

Location

Open in Google Maps
CarriesSwtwater Spring RD
CrossesPorter Creek
Location6.1 MI W Armstrong RD
RouteCounty Highway 0
CountySonoma County
StateCalifornia
Coordinates38.54568, -122.94134
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.
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 protection7 GoodSome minor problems.
Last inspectionJuly 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourUnknown foundation; not evaluated for scour
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 rating110 US tons
Inventory rating74.6 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialSteel Continuous
DeckConcrete, cast-in-place
Main spans3
Design loadUnknown
Structure length40 ft (12.2 m)
Longest span14 ft (4.4 m)
Deck width14 ft (4.3 m)
Roadway width13 ft (4.1 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic140 (2015)
Projected traffic105 by 2040
Trucks1%
Lanes on structure1
Traffic directionOne-lane bridge for two-way traffic
CarriesHighway
CrossesWaterway
Detour if closed21.1 mi (34 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 Swtwater Spring RD over Porter Creek built?

It was built in 1974, making it 51 years old in 2025.

What condition is Swtwater Spring RD over Porter 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 July 2023.

How much traffic does Swtwater Spring RD over Porter Creek carry?

About 140 vehicles per day (2015 count), of which roughly 1% are trucks.

How long is Swtwater Spring RD over Porter Creek?

The structure is 40 ft (12.2 m) long with a longest span of 14 ft (4.4 m) and a deck 14 ft wide.

Who owns Swtwater Spring RD over Porter Creek?

It is owned by the County Highway Agency.