US Bridges

Larson RD over So Slough Stillaguamish

Fair

Snohomish County, Washington · 0.6 W JCT Pioneer Hy · Structure no. 079892000000000

Built
1963
62 years old
Condition
Fair
inspected June 2024
Type
Stringer/Multi-beam or Girder
Steel Continuous
Length
302 ft
1 main span
Daily traffic
3,455
2023 count
Owner
County
County Highway Agency

About this bridge

Larson RD over So Slough Stillaguamish is a steel continuous stringer/multi-beam or girder carrying Larson RD over So Slough Stillaguamish in Snohomish County, Washington. It was built in 1963, so it is 62 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 3,455 vehicles a day, roughly 13% of them trucks, projected to reach 5,000 by 2042. The structure is 302 ft (92 m) long and 31 ft wide. If it were closed, the detour would be 8.7 mi (14 km).

Location

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CarriesLarson RD
CrossesSo Slough Stillaguamish
Location0.6 W JCT Pioneer Hy
RouteCounty Highway 96847
CountySnohomish County
StateWashington
Coordinates48.19896, -122.26514
Functional classRural Minor 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.
Superstructure6 SatisfactoryStructural elements show some minor deterioration.
Substructure7 GoodSome minor problems.
Channel and channel protection6 SatisfactoryStructural elements show some minor deterioration.
Last inspectionJune 2024
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour within limits of footing or piles
Structural evaluation6: Equal to present minimum criteria
Deck geometry3: Basically intolerable, requiring high priority of corrective action
Waterway adequacy6: Equal to present minimum criteria
Approach roadway alignment6: Equal to present minimum criteria
Operating rating50 US tons
Inventory rating29 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialSteel Continuous
DeckConcrete, cast-in-place
Main spans1 (+2 approach)
Design loadH 15
Structure length302 ft (92 m)
Longest span160 ft (48.8 m)
Deck width31 ft (9.3 m)
Roadway width26 ft (8 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic3,455 (2023)
Projected traffic5,000 by 2042
Trucks13%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed8.7 mi (14 km)
TollOn a free road
National Highway SystemNo

Ownership and planned work

OwnerCounty Highway Agency
Maintained byCounty Highway Agency
Historic statusHistorical significance not determinable at this time
Work proposedReplacement because of substandard load-carrying capacity or roadway geometry
Estimated improvement cost$11.3 million (2022 estimate)
NavigationNo navigation control on waterway

Frequently asked questions

When was Larson RD over So Slough Stillaguamish built?

It was built in 1963, making it 62 years old in 2025.

What condition is Larson RD over So Slough Stillaguamish 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 June 2024.

How much traffic does Larson RD over So Slough Stillaguamish carry?

About 3,455 vehicles per day (2023 count), of which roughly 13% are trucks.

How long is Larson RD over So Slough Stillaguamish?

The structure is 302 ft (92 m) long with a longest span of 160 ft (48.8 m) and a deck 31 ft wide.

Who owns Larson RD over So Slough Stillaguamish?

It is owned by the County Highway Agency.