US Bridges

SR 509 over N-N Ramp

Fair

King County, Washington · 4.0 N JCT SR 518 · Structure no. 0008276F0000000

Built
1968
57 years old
Condition
Fair
inspected August 2023
Type
Box Beam or Girders - Multiple
Concrete Continuous
Length
463 ft
4 main spans
Daily traffic
10,009
2022 count
Owner
State
State Highway Agency

About this bridge

SR 509 over N-N Ramp is a concrete continuous box beam or girders - multiple carrying SR 509 over N-N Ramp 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 10,009 vehicles a day, roughly 5% of them trucks, projected to reach 16,454 by 2039. The structure is 463 ft (141.1 m) long and 27 ft wide. If it were closed, the detour would be 1.9 mi (3 km).

Location

Open in Google Maps
CarriesSR 509
CrossesN-N Ramp
Location4.0 N JCT SR 518
RouteState Highway 509
CountyKing County
StateWashington
Coordinates47.52475, -122.33411
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
Deck7 GoodSome minor problems.
Superstructure6 SatisfactoryStructural elements show some minor deterioration.
Substructure7 GoodSome minor problems.
Last inspectionAugust 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourBridge not over waterway
Structural evaluation6: Equal to present minimum criteria
Deck geometry7: Better than present minimum criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating99 US tons
Inventory rating61.9 US tons

Structure

Structure typeBox Beam or Girders - Multiple
MaterialConcrete Continuous
DeckConcrete, cast-in-place
Main spans4
Design loadHS 20
Structure length463 ft (141.1 m)
Longest span150 ft (45.7 m)
Deck width27 ft (8.2 m)
Roadway width24 ft (7.3 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic10,009 (2022)
Projected traffic16,454 by 2039
Trucks5%
Lanes on structure1
Traffic directionOne-way traffic
CarriesHighway
CrossesHighway
Detour if closed1.9 mi (3 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$5.7 million (2022 estimate)
NavigationNot applicable (no waterway)

Frequently asked questions

When was SR 509 over N-N Ramp built?

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

What condition is SR 509 over N-N Ramp 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 2023.

How much traffic does SR 509 over N-N Ramp carry?

About 10,009 vehicles per day (2022 count), of which roughly 5% are trucks.

How long is SR 509 over N-N Ramp?

The structure is 463 ft (141.1 m) long with a longest span of 150 ft (45.7 m) and a deck 27 ft wide.

Who owns SR 509 over N-N Ramp?

It is owned by the State Highway Agency.