US Bridges

SR 18 over Bnrr Auburn-Blk Diamond

Good

King County, Washington · 2.3 E JCT SR 164 · Structure no. 0006068B0000000

Built
1959
66 years old, rebuilt 1992
Condition
Good
inspected July 2024
Type
Stringer/Multi-beam or Girder
Prestressed Concrete
Length
307 ft
4 main spans
Daily traffic
27,343
2023 count
Owner
State
State Highway Agency

About this bridge

SR 18 over Bnrr Auburn-Blk Diamond is a prestressed concrete stringer/multi-beam or girder carrying SR 18 over Bnrr Auburn-Blk Diamond in King County, Washington. It was built in 1959 and reconstructed in 1992, 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 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 27,343 vehicles a day, roughly 11% of them trucks, projected to reach 39,584 by 2039. The structure is 307 ft (93.6 m) long and 54 ft wide. If it were closed, the detour would be 1.2 mi (2 km).

Location

Open in Google Maps
CarriesSR 18
CrossesBnrr Auburn-Blk Diamond
Location2.3 E JCT SR 164
RouteState Highway 18
CountyKing County
StateWashington
Coordinates47.30014, -122.18011
Functional classUrban Principal Arterial - Other Freeway or Expressway

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.
Last inspectionJuly 2024
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourBridge not over waterway
Structural evaluation5: Somewhat better than minimum adequacy to tolerate being left in place as is
Deck geometry4: Meets minimum tolerable limits to be left in place as is
Approach roadway alignment8: Equal to present desirable criteria
Operating rating28.2 US tons
Inventory rating21.8 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialPrestressed Concrete
DeckConcrete, cast-in-place
Main spans4
Design loadHS 20
Structure length307 ft (93.6 m)
Longest span74 ft (22.6 m)
Deck width54 ft (16.5 m)
Roadway width50 ft (15.1 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic27,343 (2023)
Projected traffic39,584 by 2039
Trucks11%
Lanes on structure3
Traffic directionOne-way traffic
CarriesHighway
CrossesHighway and railroad
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$7.3 million (2022 estimate)
NavigationNot applicable (no waterway)

Frequently asked questions

When was SR 18 over Bnrr Auburn-Blk Diamond built?

It was built in 1959, making it 66 years old in 2025. It was reconstructed in 1992.

What condition is SR 18 over Bnrr Auburn-Blk Diamond 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 July 2024.

How much traffic does SR 18 over Bnrr Auburn-Blk Diamond carry?

About 27,343 vehicles per day (2023 count), of which roughly 11% are trucks.

How long is SR 18 over Bnrr Auburn-Blk Diamond?

The structure is 307 ft (93.6 m) long with a longest span of 74 ft (22.6 m) and a deck 54 ft wide.

Who owns SR 18 over Bnrr Auburn-Blk Diamond?

It is owned by the State Highway Agency.