US Bridges

I-90 Ramp over Mercer Slough I-90

Good

King County, Washington · 6.4 E JCT I-5 · Structure no. 0014177A0000000

Built
1995
30 years old
Condition
Good
inspected June 2023
Type
Stringer/Multi-beam or Girder
Steel Continuous
Length
2,996 ft
13 main spans
Daily traffic
2,421
2010 count
Owner
State
State Highway Agency

About this bridge

I-90 Ramp over Mercer Slough I-90 is a steel continuous stringer/multi-beam or girder carrying I-90 Ramp over Mercer Slough I-90 in King County, Washington. It was built in 1995, so it is 30 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 7 out of 9. All primary components (deck, superstructure, substructure, or culvert) are rated 7 or higher. No significant problems were noted.

It carries about 2,421 vehicles a day, roughly 5% of them trucks. The structure is 2,996 ft (913.2 m) long and 29 ft wide. If it were closed, the detour would be 1.2 mi (2 km).

Location

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CarriesI-90 Ramp
CrossesMercer Slough I-90
Location6.4 E JCT I-5
RouteInterstate 90
CountyKing County
StateWashington
Coordinates47.58075, -122.17883
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
Deck7 GoodSome minor problems.
Superstructure7 GoodSome minor problems.
Substructure7 GoodSome minor problems.
Channel and channel protection8 Very GoodNo problems noted.
Last inspectionJune 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour above top of footing
Structural evaluation7: Better than present minimum criteria
Deck geometry8: Equal to present desirable criteria
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating65 US tons
Inventory rating39 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialSteel Continuous
DeckConcrete, cast-in-place
Main spans13 (+3 approach)
Design loadHS 25 or greater
Structure length2,996 ft (913.2 m)
Longest span257 ft (78.3 m)
Deck width29 ft (8.8 m)
Roadway width26 ft (7.9 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic2,421 (2010)
Projected traffic—
Trucks5%
Lanes on structure1
Traffic directionOne-way traffic
CarriesHighway
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 statusHistorical significance not determinable at this time
Work proposedRehabilitation because of general structure deterioration or inadequate strength
Estimated improvement cost$39.8 million (2022 estimate)
NavigationNo navigation control on waterway

Frequently asked questions

When was I-90 Ramp over Mercer Slough I-90 built?

It was built in 1995, making it 30 years old in 2025.

What condition is I-90 Ramp over Mercer Slough 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 June 2023.

How much traffic does I-90 Ramp over Mercer Slough I-90 carry?

About 2,421 vehicles per day (2010 count), of which roughly 5% are trucks.

How long is I-90 Ramp over Mercer Slough I-90?

The structure is 2,996 ft (913.2 m) long with a longest span of 257 ft (78.3 m) and a deck 29 ft wide.

Who owns I-90 Ramp over Mercer Slough I-90?

It is owned by the State Highway Agency.