US Bridges

SR 9 over Slough

Fair

Whatcom County, Washington · 9.2 N Skagit CO · Structure no. 0004281C0000000

Built
1952
73 years old, rebuilt 1976
Condition
Fair
inspected August 2024
Type
Slab
Wood or Timber
Length
36 ft
2 main spans
Daily traffic
3,517
2023 count
Owner
State
State Highway Agency

About this bridge

SR 9 over Slough is a wood or timber slab carrying SR 9 over Slough in Whatcom County, Washington. It was built in 1952 and reconstructed in 1976, so it is 73 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 3,517 vehicles a day, roughly 15% of them trucks, projected to reach 4,774 by 2039. The structure is 36 ft (11 m) long and 30 ft wide. If it were closed, the detour would be 3.7 mi (6 km).

Location

Open in Google Maps
CarriesSR 9
CrossesSlough
Location9.2 N Skagit CO
RouteState Highway 9
CountyWhatcom County
StateWashington
Coordinates48.77242, -122.20164
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.
Superstructure7 GoodSome minor problems.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Channel and channel protection8 Very GoodNo problems noted.
Last inspectionAugust 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 geometry4: Meets minimum tolerable limits to be left in place as is
Waterway adequacy6: Equal to present minimum criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating70 US tons
Inventory rating50 US tons

Structure

Structure typeSlab
MaterialWood or Timber
DeckWood or timber
Main spans2
Design loadHS 15
Structure length36 ft (11 m)
Longest span17 ft (5.2 m)
Deck width30 ft (9.1 m)
Roadway width30 ft (9 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic3,517 (2023)
Projected traffic4,774 by 2039
Trucks15%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed3.7 mi (6 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$530,000 (2022 estimate)
NavigationNo navigation control on waterway

Frequently asked questions

When was SR 9 over Slough built?

It was built in 1952, making it 73 years old in 2025. It was reconstructed in 1976.

What condition is SR 9 over 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 August 2024.

How much traffic does SR 9 over Slough carry?

About 3,517 vehicles per day (2023 count), of which roughly 15% are trucks.

How long is SR 9 over Slough?

The structure is 36 ft (11 m) long with a longest span of 17 ft (5.2 m) and a deck 30 ft wide.

Who owns SR 9 over Slough?

It is owned by the State Highway Agency.