US Bridges

SR 509 over S 128th ST

Fair

King County, Washington · 1.3 N JCT SR 518 · Structure no. 0008276C0000000

Built
1968
57 years old
Condition
Fair
inspected May 2023
Type
Stringer/Multi-beam or Girder
Prestressed Concrete Continuous
Length
203 ft
3 main spans
Daily traffic
21,456
2023 count
Owner
State
State Highway Agency

About this bridge

SR 509 over S 128th ST is a prestressed concrete continuous stringer/multi-beam or girder carrying SR 509 over S 128th ST in King 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 21,456 vehicles a day, roughly 3% of them trucks, projected to reach 32,252 by 2039. The structure is 203 ft (61.9 m) long and 85 ft wide. If it were closed, the detour would be 1.2 mi (2 km).

Location

Open in Google Maps
CarriesSR 509
CrossesS 128th ST
Location1.3 N JCT SR 518
RouteState Highway 509
CountyKing County
StateWashington
Coordinates47.48836, -122.32614
Functional classUrban Principal Arterial - Other Freeway or Expressway

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.
Substructure7 GoodSome minor problems.
Last inspectionMay 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourBridge not over waterway
Structural evaluation6: Equal to present minimum criteria
Deck geometry9: Superior to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating35.4 US tons
Inventory rating27.1 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialPrestressed Concrete Continuous
DeckConcrete, cast-in-place
Main spans3
Design loadHS 20
Structure length203 ft (61.9 m)
Longest span108 ft (32.9 m)
Deck width85 ft (25.9 m)
Roadway width82 ft (25 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic21,456 (2023)
Projected traffic32,252 by 2039
Trucks3%
Lanes on structure4
Traffic directionOne-way traffic
CarriesHighway
CrossesHighway
Detour if closed1.2 mi (2 km)
TollOn a free road
National Highway SystemYes

Ownership and planned work

OwnerState Highway Agency
Maintained byState Highway Agency
Historic statusHistorical significance not determinable at this time
Work proposedRehabilitation because of general structure deterioration or inadequate strength
Estimated improvement cost$8.1 million (2022 estimate)
NavigationNot applicable (no waterway)

Frequently asked questions

When was SR 509 over S 128th ST built?

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

What condition is SR 509 over S 128th ST 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 May 2023.

How much traffic does SR 509 over S 128th ST carry?

About 21,456 vehicles per day (2023 count), of which roughly 3% are trucks.

How long is SR 509 over S 128th ST?

The structure is 203 ft (61.9 m) long with a longest span of 108 ft (32.9 m) and a deck 85 ft wide.

Who owns SR 509 over S 128th ST?

It is owned by the State Highway Agency.