US Bridges

I-5 over Steamboat Slough

Fair

Snohomish County, Washington · 4.1 N JCT US 2 · Structure no. 0008226D0000000

Built
1968
57 years old
Condition
Fair
inspected March 2024
Type
Stringer/Multi-beam or Girder
Prestressed Concrete Continuous
Length
1,026 ft
9 main spans
Daily traffic
64,989
2023 count
Owner
State
State Highway Agency

About this bridge

I-5 over Steamboat Slough is a prestressed concrete continuous stringer/multi-beam or girder carrying I-5 over Steamboat Slough in Snohomish County, Washington. It was built in 1968, so it is 57 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 64,989 vehicles a day, roughly 6% of them trucks, projected to reach 95,649 by 2039. The structure is 1,026 ft (312.7 m) long and 52 ft wide. If it were closed, the detour would be 1.2 mi (2 km).

Location

Open in Google Maps
CarriesI-5
CrossesSteamboat Slough
Location4.1 N JCT US 2
RouteInterstate 5
CountySnohomish County
StateWashington
Coordinates48.035, -122.17786
Functional classUrban Principal Arterial - Interstate

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.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Channel and channel protection7 GoodSome minor problems.
Last inspectionMarch 2024
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourCountermeasures installed to correct a previously existing problem
Structural evaluation5: Somewhat better than minimum adequacy to tolerate being left in place as is
Deck geometry4: Meets minimum tolerable limits to be left in place as is
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating35.4 US tons
Inventory rating22.5 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialPrestressed Concrete Continuous
DeckConcrete, cast-in-place
Main spans9
Design loadHS 20 + Mod
Structure length1,026 ft (312.7 m)
Longest span121 ft (36.9 m)
Deck width52 ft (15.7 m)
Roadway width48 ft (14.6 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic64,989 (2023)
Projected traffic95,649 by 2039
Trucks6%
Lanes on structure3
Traffic directionOne-way traffic
CarriesHighway
CrossesWaterway
Detour if closed1.2 mi (2 km)
TollOn a free road
National Highway SystemYes
Strategic Highway NetworkInterstate STRAHNET route

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$27.3 million (2022 estimate)
NavigationNavigation control on waterway (bridge permit required)

Frequently asked questions

When was I-5 over Steamboat Slough built?

It was built in 1968, making it 57 years old in 2025.

What condition is I-5 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 March 2024.

How much traffic does I-5 over Steamboat Slough carry?

About 64,989 vehicles per day (2023 count), of which roughly 6% are trucks.

How long is I-5 over Steamboat Slough?

The structure is 1,026 ft (312.7 m) long with a longest span of 121 ft (36.9 m) and a deck 52 ft wide.

Who owns I-5 over Steamboat Slough?

It is owned by the State Highway Agency.