US Bridges

Laconner Whitney R over Sullivan Slough

Fair

Skagit County, Washington · 3.83 S JCT SR 20 · Structure no. 084170000000000

Built
1962
63 years old
Condition
Fair
inspected September 2023
Type
Stringer/Multi-beam or Girder
Prestressed Concrete
Length
68 ft
1 main span
Daily traffic
5,550
2023 count
Owner
County
County Highway Agency

About this bridge

Laconner Whitney R over Sullivan Slough is a prestressed concrete stringer/multi-beam or girder carrying Laconner Whitney R over Sullivan Slough in Skagit County, Washington. It was built in 1962, so it is 63 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 5,550 vehicles a day, roughly 6% of them trucks, projected to reach 10,024 by 2043. The structure is 68 ft (20.7 m) long and 28 ft wide. If it were closed, the detour would be 8.1 mi (13 km).

Location

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CarriesLaconner Whitney R
CrossesSullivan Slough
Location3.83 S JCT SR 20
RouteCounty Highway 42410
CountySkagit County
StateWashington
Coordinates48.39481, -122.48464
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
Deck7 GoodSome minor problems.
Superstructure6 SatisfactoryStructural elements show some minor deterioration.
Substructure7 GoodSome minor problems.
Channel and channel protection8 Very GoodNo problems noted.
Last inspectionSeptember 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour within limits of footing or piles
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 adequacy7: Better than present minimum criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating37.5 US tons
Inventory rating22.5 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialPrestressed Concrete
DeckConcrete, cast-in-place
Main spans1
Design loadHS 20
Structure length68 ft (20.7 m)
Longest span65 ft (19.8 m)
Deck width28 ft (8.5 m)
Roadway width26 ft (7.9 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic5,550 (2023)
Projected traffic10,024 by 2043
Trucks6%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed8.1 mi (13 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 proposedRehabilitation because of general structure deterioration or inadequate strength
Estimated improvement cost$1.2 million (2022 estimate)
NavigationNo navigation control on waterway

Frequently asked questions

When was Laconner Whitney R over Sullivan Slough built?

It was built in 1962, making it 63 years old in 2025.

What condition is Laconner Whitney R over Sullivan 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 September 2023.

How much traffic does Laconner Whitney R over Sullivan Slough carry?

About 5,550 vehicles per day (2023 count), of which roughly 6% are trucks.

How long is Laconner Whitney R over Sullivan Slough?

The structure is 68 ft (20.7 m) long with a longest span of 65 ft (19.8 m) and a deck 28 ft wide.

Who owns Laconner Whitney R over Sullivan Slough?

It is owned by the County Highway Agency.