US Bridges

I-405 N-W Ramp over Sammamish R I-405 SR 5

Fair

King County, Washington · 8.7 N JCT SR 520 · Structure no. 0008382D0000000

Built
1968
57 years old
Condition
Fair
inspected November 2024
Type
Box Beam or Girders - Multiple
Concrete Continuous
Length
1,469 ft
15 main spans
Daily traffic
8,770
2023 count
Owner
State
State Highway Agency

About this bridge

I-405 N-W Ramp over Sammamish R I-405 SR 5 is a concrete continuous box beam or girders - multiple carrying I-405 N-W Ramp over Sammamish R I-405 SR 5 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 8,770 vehicles a day, roughly 5% of them trucks, projected to reach 10,200 by 2036. The structure is 1,469 ft (447.8 m) long and 28 ft wide. If it were closed, the detour would be 1.2 mi (2 km).

Location

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CarriesI-405 N-W Ramp
CrossesSammamish R I-405 SR 5
Location8.7 N JCT SR 520
RouteInterstate 405
CountyKing County
StateWashington
Coordinates47.75597, -122.18503
Functional classUrban Principal Arterial - Interstate

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.
Channel and channel protection8 Very GoodNo problems noted.
Last inspectionNovember 2024
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour within limits of footing or piles
Structural evaluation6: Equal to present minimum criteria
Deck geometry5: Somewhat better than minimum adequacy to tolerate being left in place as is
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating55.7 US tons
Inventory rating43.2 US tons

Structure

Structure typeBox Beam or Girders - Multiple
MaterialConcrete Continuous
DeckConcrete, cast-in-place
Main spans15
Design loadHS 20
Structure length1,469 ft (447.8 m)
Longest span109 ft (33.2 m)
Deck width28 ft (8.4 m)
Roadway width24 ft (7.3 m)
Vertical clearance over deck16 ft (5 m)

Traffic and service

Average daily traffic8,770 (2023)
Projected traffic10,200 by 2036
Trucks5%
Lanes on structure1
Traffic directionOne-way traffic
CarriesOverpass structure at an interchange
CrossesHighway and waterway
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$19.5 million (2022 estimate)
NavigationNavigation control on waterway (bridge permit required)

Frequently asked questions

When was I-405 N-W Ramp over Sammamish R I-405 SR 5 built?

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

What condition is I-405 N-W Ramp over Sammamish R I-405 SR 5 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 November 2024.

How much traffic does I-405 N-W Ramp over Sammamish R I-405 SR 5 carry?

About 8,770 vehicles per day (2023 count), of which roughly 5% are trucks.

How long is I-405 N-W Ramp over Sammamish R I-405 SR 5?

The structure is 1,469 ft (447.8 m) long with a longest span of 109 ft (33.2 m) and a deck 28 ft wide.

Who owns I-405 N-W Ramp over Sammamish R I-405 SR 5?

It is owned by the State Highway Agency.