US Bridges

SR 409 over Birnie Slough

Fair

Wahkiakum County, Washington · 1.8 N Ferry Dock · Structure no. 0003264A0000000

Built
1947
78 years old
Condition
Fair
inspected April 2024
Type
Stringer/Multi-beam or Girder
Steel
Length
193 ft
5 main spans
Daily traffic
906
2023 count
Owner
State
State Highway Agency

About this bridge

SR 409 over Birnie Slough is a steel stringer/multi-beam or girder carrying SR 409 over Birnie Slough in Wahkiakum County, Washington. It was built in 1947, so it is 78 years old, older than the Washington average of 49.8 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 906 vehicles a day, roughly 6% of them trucks, projected to reach 938 by 2039. The structure is 193 ft (58.8 m) long and 32 ft wide. If it were closed, the detour would be 98.8 mi (159 km).

Location

Open in Google Maps
CarriesSR 409
CrossesBirnie Slough
Location1.8 N Ferry Dock
RouteState Highway 409
CountyWahkiakum County
StateWashington
Coordinates46.1795, -123.37708
Functional classRural Major 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
Deck6 SatisfactoryStructural elements show some minor deterioration.
Superstructure7 GoodSome minor problems.
Substructure7 GoodSome minor problems.
Channel and channel protection6 SatisfactoryStructural elements show some minor deterioration.
Last inspectionApril 2024
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour within limits of footing or piles
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 US tons
Inventory rating32 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialSteel
DeckConcrete, cast-in-place
Main spans5
Design loadH 15
Structure length193 ft (58.8 m)
Longest span60 ft (18.3 m)
Deck width32 ft (9.9 m)
Roadway width26 ft (7.9 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic906 (2023)
Projected traffic938 by 2039
Trucks6%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway and pedestrian
CrossesWaterway
Detour if closed98.8 mi (159 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 proposedRehabilitation because of general structure deterioration or inadequate strength
Estimated improvement cost$2.6 million (2022 estimate)
NavigationNo navigation control on waterway

Frequently asked questions

When was SR 409 over Birnie Slough built?

It was built in 1947, making it 78 years old in 2025.

What condition is SR 409 over Birnie Slough 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 SR 409 over Birnie Slough carry?

About 906 vehicles per day (2023 count), of which roughly 6% are trucks.

How long is SR 409 over Birnie Slough?

The structure is 193 ft (58.8 m) long with a longest span of 60 ft (18.3 m) and a deck 32 ft wide.

Who owns SR 409 over Birnie Slough?

It is owned by the State Highway Agency.