US Bridges

SR 518 over SR 509

Fair

King County, Washington · JCT SR 509 · Structure no. 0008745E0000000

Built
1971
54 years old
Condition
Fair
inspected March 2024
Type
Stringer/Multi-beam or Girder
Prestressed Concrete Continuous
Length
241 ft
4 main spans
Daily traffic
40,718
2023 count
Owner
State
State Highway Agency

About this bridge

SR 518 over SR 509 is a prestressed concrete continuous stringer/multi-beam or girder carrying SR 518 over SR 509 in King County, Washington. It was built in 1971, so it is 54 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 40,718 vehicles a day, roughly 2% of them trucks, projected to reach 64,203 by 2039. The structure is 241 ft (73.5 m) long and 105 ft wide. If it were closed, the detour would be 1.2 mi (2 km).

Location

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CarriesSR 518
CrossesSR 509
LocationJCT SR 509
RouteState Highway 518
CountyKing County
StateWashington
Coordinates47.47033, -122.33214
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.
Superstructure7 GoodSome minor problems.
Substructure7 GoodSome minor problems.
Last inspectionMarch 2024
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourBridge not over waterway
Structural evaluation4: Meets minimum tolerable limits to be left in place as is
Deck geometry4: Meets minimum tolerable limits to be left in place as is
Approach roadway alignment8: Equal to present desirable criteria
Operating rating23.6 US tons
Inventory rating18.2 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialPrestressed Concrete Continuous
DeckConcrete, cast-in-place
Main spans4
Design loadHS 20
Structure length241 ft (73.5 m)
Longest span77 ft (23.5 m)
Deck width105 ft (32 m)
Roadway width94 ft (28.7 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic40,718 (2023)
Projected traffic64,203 by 2039
Trucks2%
Lanes on structure7
Traffic directionTwo-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 statusNot eligible for the National Register of Historic Places
Work proposedRehabilitation because of general structure deterioration or inadequate strength
Estimated improvement cost$11 million (2022 estimate)
NavigationNot applicable (no waterway)

Frequently asked questions

When was SR 518 over SR 509 built?

It was built in 1971, making it 54 years old in 2025.

What condition is SR 518 over SR 509 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 March 2024.

How much traffic does SR 518 over SR 509 carry?

About 40,718 vehicles per day (2023 count), of which roughly 2% are trucks.

How long is SR 518 over SR 509?

The structure is 241 ft (73.5 m) long with a longest span of 77 ft (23.5 m) and a deck 105 ft wide.

Who owns SR 518 over SR 509?

It is owned by the State Highway Agency.