US Bridges

Seattle Blvd over Sound Transit Tunnel

Fair

King County, Washington · Seattle Blvd Eo 4th Ave S · Structure no. 085041000000000

Built
1910
115 years old, rebuilt 1981
Condition
Fair
inspected August 2023
Type
Girder and Floorbeam System
Steel
Length
287 ft
3 main spans
Daily traffic
22,000
2019 count
Owner
City
City or Municipal Highway Agency

About this bridge

Seattle Blvd over Sound Transit Tunnel is a steel girder and floorbeam system carrying Seattle Blvd over Sound Transit Tunnel in King County, Washington. It was built in 1910 and reconstructed in 1981, so it is 115 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 22,000 vehicles a day, roughly 5% of them trucks, projected to reach 2,035 by 2041. The structure is 287 ft (87.5 m) long and 101 ft wide. If it were closed, the detour would be 1.2 mi (2 km).

Location

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CarriesSeattle Blvd
CrossesSound Transit Tunnel
LocationSeattle Blvd Eo 4th Ave S
RouteCity Street 1140
CountyKing County
StateWashington
Coordinates47.59611, -122.32833
Functional classUrban Other Principal Arterial

Condition and inspection

Fair

The lowest-rated primary component is rated 5 or 6. Minor deterioration is present but the structure is sound.

ComponentRatingMeaning
Deck6 SatisfactoryStructural elements show some minor deterioration.
Superstructure6 SatisfactoryStructural elements show some minor deterioration.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Last inspectionAugust 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourBridge not over waterway
Structural evaluation6: Equal to present minimum criteria
Deck geometry2: Basically intolerable, requiring high priority of replacement
Approach roadway alignment8: Equal to present desirable criteria
Operating rating47 US tons
Inventory rating28 US tons

Structure

Structure typeGirder and Floorbeam System
MaterialSteel
DeckConcrete, cast-in-place
Main spans3 (+4 approach)
Design loadHS 25 or greater
Structure length287 ft (87.5 m)
Longest span75 ft (22.9 m)
Deck width101 ft (30.8 m)
Roadway width68 ft (20.7 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic22,000 (2019)
Projected traffic2,035 by 2041
Trucks5%
Lanes on structure6
Traffic directionTwo-way traffic
CarriesHighway and pedestrian
CrossesRailroad
Detour if closed1.2 mi (2 km)
TollOn a free road
National Highway SystemYes

Ownership and planned work

OwnerCity or Municipal Highway Agency
Maintained byCity or Municipal Highway Agency
Historic statusNot eligible for the National Register of Historic Places
Work proposedReplacement because of substandard load-carrying capacity or roadway geometry
Estimated improvement cost$1.9 million
NavigationNot applicable (no waterway)

Frequently asked questions

When was Seattle Blvd over Sound Transit Tunnel built?

It was built in 1910, making it 115 years old in 2025. It was reconstructed in 1981.

What condition is Seattle Blvd over Sound Transit Tunnel 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 August 2023.

How much traffic does Seattle Blvd over Sound Transit Tunnel carry?

About 22,000 vehicles per day (2019 count), of which roughly 5% are trucks.

How long is Seattle Blvd over Sound Transit Tunnel?

The structure is 287 ft (87.5 m) long with a longest span of 75 ft (22.9 m) and a deck 101 ft wide.

Who owns Seattle Blvd over Sound Transit Tunnel?

It is owned by the City or Municipal Highway Agency.