US Bridges

SR 203 over Slough

Poor

King County, Washington · 0.5 N JCT SR 202 · Structure no. 0002999B0000000

Built
1945
80 years old
Condition
Poor
inspected July 2023
Type
Stringer/Multi-beam or Girder
Wood or Timber
Length
52 ft
3 main spans
Daily traffic
7,813
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 poor condition with a lowest component rating of 4 out of 9. The lowest-rated primary component is rated 4 or below, indicating advanced deterioration. Poor does not mean unsafe; such bridges are inspected more often and may carry load restrictions.

It carries about 7,813 vehicles a day, roughly 10% of them trucks, projected to reach 10,989 by 2039. The structure is 52 ft (15.8 m) long and 39 ft wide. If it were closed, the detour would be 5 mi (8 km).

Location

Open in Google Maps
CarriesSR 203
CrossesSlough
Location0.5 N JCT SR 202
RouteState Highway 203
CountyKing County
StateWashington
Coordinates47.5755, -121.89044
Functional classRural Minor Arterial

Condition and inspection

Poor

The lowest-rated primary component is rated 4 or below, indicating advanced deterioration. Poor does not mean unsafe; such bridges are inspected more often and may carry load restrictions.

ComponentRatingMeaning
Deck4 PoorAdvanced section loss, deterioration, spalling or scour.
Superstructure7 GoodSome minor problems.
Substructure5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
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 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 adequacy6: Equal to present minimum criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating48.9 US tons
Inventory rating34 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialWood or Timber
DeckConcrete, cast-in-place
Main spans3
Design loadH 15
Structure length52 ft (15.8 m)
Longest span17 ft (5.2 m)
Deck width39 ft (11.8 m)
Roadway width36 ft (11 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic7,813 (2023)
Projected traffic10,989 by 2039
Trucks10%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesRelief for waterway
Detour if closed5 mi (8 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$790,000 (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 poor condition. The lowest-rated primary component is rated 4 or below, indicating advanced deterioration. Poor does not mean unsafe; such bridges are inspected more often and may carry load restrictions. The last reported inspection was in July 2023.

How much traffic does SR 203 over Slough carry?

About 7,813 vehicles per day (2023 count), of which roughly 10% are trucks.

How long is SR 203 over Slough?

The structure is 52 ft (15.8 m) long with a longest span of 17 ft (5.2 m) and a deck 39 ft wide.

Who owns SR 203 over Slough?

It is owned by the State Highway Agency.