US Bridges

SW Michigan ST over Wetland Mit. Channel

Good

King County, Washington · Under S Appr 99/530 · Structure no. 0014459C0000000

Built
1996
29 years old
Condition
Good
inspected September 2023
Type
Slab
Concrete
Length
64 ft
1 main span
Daily traffic
515
2002 count
Owner
State
State Highway Agency

About this bridge

SW Michigan ST over Wetland Mit. Channel is a concrete slab carrying SW Michigan ST over Wetland Mit. Channel in King County, Washington. It was built in 1996, so it is 29 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 515 vehicles a day, roughly 5% of them trucks, projected to reach 690 by 2036. The structure is 64 ft (19.5 m) long and 38 ft wide. If it were closed, the detour would be 1.2 mi (2 km).

Location

Open in Google Maps
CarriesSW Michigan ST
CrossesWetland Mit. Channel
LocationUnder S Appr 99/530
RouteCity Street 99
CountyKing County
StateWashington
Coordinates47.54065, -122.33496
Functional classUrban Local

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 protection5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Last inspectionSeptember 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour within limits of footing or piles
Structural evaluation7: Better than present minimum criteria
Deck geometry7: Better than present minimum criteria
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment6: Equal to present minimum criteria
Operating rating59 US tons
Inventory rating34.9 US tons

Structure

Structure typeSlab
MaterialConcrete
DeckConcrete, cast-in-place
Main spans1
Design loadHS 25 or greater
Structure length64 ft (19.5 m)
Longest span64 ft (19.5 m)
Deck width38 ft (11.7 m)
Roadway width36 ft (11 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic515 (2002)
Projected traffic690 by 2036
Trucks5%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed1.2 mi (2 km)
TollOn a free road
National Highway SystemNo

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$1.2 million (2022 estimate)
NavigationNo navigation control on waterway

Frequently asked questions

When was SW Michigan ST over Wetland Mit. Channel built?

It was built in 1996, making it 29 years old in 2025.

What condition is SW Michigan ST over Wetland Mit. Channel 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 September 2023.

How much traffic does SW Michigan ST over Wetland Mit. Channel carry?

About 515 vehicles per day (2002 count), of which roughly 5% are trucks.

How long is SW Michigan ST over Wetland Mit. Channel?

The structure is 64 ft (19.5 m) long with a longest span of 64 ft (19.5 m) and a deck 38 ft wide.

Who owns SW Michigan ST over Wetland Mit. Channel?

It is owned by the State Highway Agency.