US Bridges

SR 529 over Steamboat Slough

Fair

Snohomish County, Washington · 6.3 N JCT SR 529 Spur · Structure no. 0004373A0000000

Built
1954
71 years old
Condition
Fair
inspected July 2024
Type
Movable - Swing
Steel
Length
910 ft
2 main spans
Daily traffic
16,592
2023 count
Owner
State
State Highway Agency

About this bridge

SR 529 over Steamboat Slough is a steel movable - swing carrying SR 529 over Steamboat Slough in Snohomish County, Washington. It was built in 1954, so it is 71 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 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 16,592 vehicles a day, roughly 6% of them trucks, projected to reach 24,319 by 2039. The structure is 910 ft (277.4 m) long and 34 ft wide. If it were closed, the detour would be 1.2 mi (2 km).

Location

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CarriesSR 529
CrossesSteamboat Slough
Location6.3 N JCT SR 529 Spur
RouteState Highway 529
CountySnohomish County
StateWashington
Coordinates48.03489, -122.1815
Functional classUrban Principal Arterial - Other Freeway or Expressway

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.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Channel and channel protection7 GoodSome minor problems.
Last inspectionJuly 2024
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourScour critical; foundations unstable for calculated scour conditions
Structural evaluation5: Somewhat better than minimum adequacy to tolerate being left in place as is
Deck geometry3: Basically intolerable, requiring high priority of corrective action
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating52 US tons
Inventory rating31 US tons

Structure

Structure typeMovable - Swing
MaterialSteel
DeckConcrete, cast-in-place
Main spans2 (+10 approach)
Design loadHS 20
Structure length910 ft (277.4 m)
Longest span182 ft (55.5 m)
Deck width34 ft (10.4 m)
Roadway width28 ft (8.5 m)
Vertical clearance over deck15 ft (4.6 m)

Traffic and service

Average daily traffic16,592 (2023)
Projected traffic24,319 by 2039
Trucks6%
Lanes on structure2
Traffic directionOne-way traffic
CarriesHighway and pedestrian
CrossesHighway and waterway
Detour if closed1.2 mi (2 km)
TollOn a free road
National Highway SystemYes

Ownership and planned work

OwnerState Highway Agency
Maintained byState Highway Agency
Historic statusPossibly eligible for the National Register; requires further investigation
Work proposedRehabilitation because of general structure deterioration or inadequate strength
Estimated improvement cost$13.8 million (2022 estimate)
NavigationNavigation control on waterway (bridge permit required)

Frequently asked questions

When was SR 529 over Steamboat Slough built?

It was built in 1954, making it 71 years old in 2025.

What condition is SR 529 over Steamboat 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 July 2024.

How much traffic does SR 529 over Steamboat Slough carry?

About 16,592 vehicles per day (2023 count), of which roughly 6% are trucks.

How long is SR 529 over Steamboat Slough?

The structure is 910 ft (277.4 m) long with a longest span of 182 ft (55.5 m) and a deck 34 ft wide.

Who owns SR 529 over Steamboat Slough?

It is owned by the State Highway Agency.