US Bridges

N-N Ramp over SR 599 SB / SR 99 SB

Fair

King County, Washington · 2.4 N JCT SR 518 · Structure no. 0007967A0000000

Built
1966
59 years old
Condition
Fair
inspected May 2024
Type
Stringer/Multi-beam or Girder
Prestressed Concrete
Length
263 ft
3 main spans
Daily traffic
1,802
2023 count
Owner
State
State Highway Agency

About this bridge

N-N Ramp over SR 599 SB / SR 99 SB is a prestressed concrete stringer/multi-beam or girder carrying N-N Ramp over SR 599 SB / SR 99 SB in King County, Washington. It was built in 1966, so it is 59 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 1,802 vehicles a day, roughly 5% of them trucks, projected to reach 3,233 by 2039. The structure is 263 ft (80.2 m) long and 26 ft wide. If it were closed, the detour would be 1.9 mi (3 km).

Location

Open in Google Maps
CarriesN-N Ramp
CrossesSR 599 SB / SR 99 SB
Location2.4 N JCT SR 518
RouteState Highway 99
CountyKing County
StateWashington
Coordinates47.49703, -122.29344
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.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Last inspectionMay 2024
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourBridge not over waterway
Structural evaluation5: Somewhat better than minimum adequacy to tolerate being left in place as is
Deck geometry6: Equal to present minimum criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating50 US tons
Inventory rating26 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialPrestressed Concrete
DeckConcrete, cast-in-place
Main spans3
Design loadHS 20 + Mod
Structure length263 ft (80.2 m)
Longest span106 ft (32.3 m)
Deck width26 ft (8 m)
Roadway width23 ft (7 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic1,802 (2023)
Projected traffic3,233 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$3.7 million (2022 estimate)
NavigationNot applicable (no waterway)

Frequently asked questions

When was N-N Ramp over SR 599 SB / SR 99 SB built?

It was built in 1966, making it 59 years old in 2025.

What condition is N-N Ramp over SR 599 SB / SR 99 SB 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 2024.

How much traffic does N-N Ramp over SR 599 SB / SR 99 SB carry?

About 1,802 vehicles per day (2023 count), of which roughly 5% are trucks.

How long is N-N Ramp over SR 599 SB / SR 99 SB?

The structure is 263 ft (80.2 m) long with a longest span of 106 ft (32.3 m) and a deck 26 ft wide.

Who owns N-N Ramp over SR 599 SB / SR 99 SB?

It is owned by the State Highway Agency.