US Bridges

SR 18 over Kent-Black Diamond RD SE

Fair

King County, Washington · 6.2 E JCT SR 164 · Structure no. 0006068C0000000

Built
1959
66 years old, rebuilt 1993
Condition
Fair
inspected March 2024
Type
Stringer/Multi-beam or Girder
Prestressed Concrete
Length
202 ft
3 main spans
Daily traffic
26,257
2023 count
Owner
State
State Highway Agency

About this bridge

SR 18 over Kent-Black Diamond RD SE is a prestressed concrete stringer/multi-beam or girder carrying SR 18 over Kent-Black Diamond RD SE in King County, Washington. It was built in 1959 and reconstructed in 1993, so it is 66 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 26,257 vehicles a day, roughly 14% of them trucks, projected to reach 37,992 by 2039. The structure is 202 ft (61.6 m) long and 35 ft wide. If it were closed, the detour would be 3.7 mi (6 km).

Location

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CarriesSR 18
CrossesKent-Black Diamond RD SE
Location6.2 E JCT SR 164
RouteState Highway 18
CountyKing County
StateWashington
Coordinates47.34789, -122.13921
Functional classUrban Principal Arterial - Other Freeway or Expressway

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.
Last inspectionMarch 2024
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourBridge not over waterway
Structural evaluation6: Equal to present minimum criteria
Deck geometry4: Meets minimum tolerable limits to be left in place as is
Approach roadway alignment8: Equal to present desirable criteria
Operating rating62.9 US tons
Inventory rating37 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialPrestressed Concrete
DeckConcrete, cast-in-place
Main spans3
Design loadHS 20
Structure length202 ft (61.6 m)
Longest span88 ft (26.8 m)
Deck width35 ft (10.7 m)
Roadway width32 ft (9.8 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic26,257 (2023)
Projected traffic37,992 by 2039
Trucks14%
Lanes on structure2
Traffic directionOne-way traffic
CarriesHighway
CrossesHighway
Detour if closed3.7 mi (6 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$4.1 million (2022 estimate)
NavigationNot applicable (no waterway)

Frequently asked questions

When was SR 18 over Kent-Black Diamond RD SE built?

It was built in 1959, making it 66 years old in 2025. It was reconstructed in 1993.

What condition is SR 18 over Kent-Black Diamond RD SE 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 March 2024.

How much traffic does SR 18 over Kent-Black Diamond RD SE carry?

About 26,257 vehicles per day (2023 count), of which roughly 14% are trucks.

How long is SR 18 over Kent-Black Diamond RD SE?

The structure is 202 ft (61.6 m) long with a longest span of 88 ft (26.8 m) and a deck 35 ft wide.

Who owns SR 18 over Kent-Black Diamond RD SE?

It is owned by the State Highway Agency.