US Bridges

I-405 over I-90

Good

King County, Washington · 5.7 N JCT SR 900 · Structure no. 0017283A0000000

Built
2008
17 years old
Condition
Good
inspected February 2023
Type
Stringer/Multi-beam or Girder
Prestressed Concrete Continuous
Length
893 ft
6 main spans
Daily traffic
48,783
2023 count
Owner
State
State Highway Agency

About this bridge

I-405 over I-90 is a prestressed concrete continuous stringer/multi-beam or girder carrying I-405 over I-90 in King County, Washington. It was built in 2008, so it is 17 years old, younger than the Washington average of 49.8 years.

The most recent inspection reported to the Federal Highway Administration rates it in good condition with a lowest component rating of 8 out of 9. All primary components (deck, superstructure, substructure, or culvert) are rated 7 or higher. No significant problems were noted.

It carries about 48,783 vehicles a day, roughly 6% of them trucks, projected to reach 71,752 by 2039. The structure is 893 ft (272.2 m) long and 59 ft wide. If it were closed, the detour would be 1.2 mi (2 km).

Location

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CarriesI-405
CrossesI-90
Location5.7 N JCT SR 900
RouteInterstate 405
CountyKing County
StateWashington
Coordinates47.57914, -122.17469
Functional classUrban Principal Arterial - Interstate

Condition and inspection

Good

All primary components (deck, superstructure, substructure, or culvert) are rated 7 or higher. No significant problems were noted.

ComponentRatingMeaning
Deck8 Very GoodNo problems noted.
Superstructure8 Very GoodNo problems noted.
Substructure8 Very GoodNo problems noted.
Last inspectionFebruary 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourBridge not over waterway
Structural evaluation8: Equal to present desirable criteria
Deck geometry6: Equal to present minimum criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating66 US tons
Inventory rating40 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialPrestressed Concrete Continuous
DeckConcrete, cast-in-place
Main spans6
Design loadHL 93
Structure length893 ft (272.2 m)
Longest span161 ft (49.1 m)
Deck width59 ft (18 m)
Roadway width56 ft (17.1 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic48,783 (2023)
Projected traffic71,752 by 2039
Trucks6%
Lanes on structure3
Traffic directionOne-way traffic
CarriesHighway
CrossesHighway
Detour if closed1.2 mi (2 km)
TollOn a free road
National Highway SystemYes
Strategic Highway NetworkInterstate STRAHNET route

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$24.6 million (2022 estimate)
NavigationNot applicable (no waterway)

Frequently asked questions

When was I-405 over I-90 built?

It was built in 2008, making it 17 years old in 2025.

What condition is I-405 over I-90 in?

The National Bridge Inventory rates it in good condition. All primary components (deck, superstructure, substructure, or culvert) are rated 7 or higher. No significant problems were noted. The last reported inspection was in February 2023.

How much traffic does I-405 over I-90 carry?

About 48,783 vehicles per day (2023 count), of which roughly 6% are trucks.

How long is I-405 over I-90?

The structure is 893 ft (272.2 m) long with a longest span of 161 ft (49.1 m) and a deck 59 ft wide.

Who owns I-405 over I-90?

It is owned by the State Highway Agency.