US Bridges

SR 203 over Slough

Good

King County, Washington · 16.6 N JCT SR 202 · Structure no. 0002999N0000000

Built
1945
80 years old
Condition
Good
inspected July 2023
Type
Stringer/Multi-beam or Girder
Wood or Timber
Length
58 ft
3 main spans
Daily traffic
10,445
2023 count
Owner
State
State Highway Agency

About this bridge

SR 203 over Slough is a wood or timber stringer/multi-beam or girder carrying SR 203 over Slough in King County, Washington. It was built in 1945, so it is 80 years old, older than the Washington average of 49.8 years.

The most recent inspection reported to the Federal Highway Administration rates it in good condition with a lowest component rating of 7 out of 9. All primary components (deck, superstructure, substructure, or culvert) are rated 7 or higher. No significant problems were noted.

It carries about 10,445 vehicles a day, roughly 9% of them trucks, projected to reach 14,690 by 2039. The structure is 58 ft (17.7 m) long and 39 ft wide. If it were closed, the detour would be 14.3 mi (23 km).

Location

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CarriesSR 203
CrossesSlough
Location16.6 N JCT SR 202
RouteState Highway 203
CountyKing County
StateWashington
Coordinates47.75987, -121.9693
Functional classRural Minor Arterial

Condition and inspection

Good

All primary components (deck, superstructure, substructure, or culvert) are rated 7 or higher. No significant problems were noted.

ComponentRatingMeaning
Deck7 GoodSome minor problems.
Superstructure7 GoodSome minor problems.
Substructure7 GoodSome minor problems.
Channel and channel protection8 Very GoodNo problems noted.
Last inspectionJuly 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour above top of footing
Structural evaluation7: Better than 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 rating52 US tons
Inventory rating36 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialWood or Timber
DeckConcrete, cast-in-place
Main spans3
Design loadH 15
Structure length58 ft (17.7 m)
Longest span19 ft (5.8 m)
Deck width39 ft (11.8 m)
Roadway width36 ft (11 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic10,445 (2023)
Projected traffic14,690 by 2039
Trucks9%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed14.3 mi (23 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$799,000 (2022 estimate)
NavigationNo navigation control on waterway

Frequently asked questions

When was SR 203 over Slough built?

It was built in 1945, making it 80 years old in 2025.

What condition is SR 203 over Slough in?

The National Bridge Inventory rates it in good condition. All primary components (deck, superstructure, substructure, or culvert) are rated 7 or higher. No significant problems were noted. The last reported inspection was in July 2023.

How much traffic does SR 203 over Slough carry?

About 10,445 vehicles per day (2023 count), of which roughly 9% are trucks.

How long is SR 203 over Slough?

The structure is 58 ft (17.7 m) long with a longest span of 19 ft (5.8 m) and a deck 39 ft wide.

Who owns SR 203 over Slough?

It is owned by the State Highway Agency.