US Bridges

SB Airport Expy over S 170th ST

Fair

King County, Washington · 1 MI S of SR 518 · Structure no. 085812000000000

Built
1972
53 years old
Condition
Fair
inspected May 2023
Type
Box Beam or Girders - Multiple
Concrete Continuous
Length
148 ft
3 main spans
Daily traffic
45,000
2016 count
Owner
Local
Other Local Agency

About this bridge

SB Airport Expy over S 170th ST is a concrete continuous box beam or girders - multiple carrying SB Airport Expy over S 170th ST in King County, Washington. It was built in 1972, so it is 53 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 45,000 vehicles a day, roughly 12% of them trucks, projected to reach 42,000 by 2036. The structure is 148 ft (45.1 m) long and 71 ft wide.

Location

Open in Google Maps
CarriesSB Airport Expy
CrossesS 170th ST
Location1 MI S of SR 518
CountyKing County
StateWashington
Coordinates47.45068, -122.30062
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
Deck7 GoodSome minor problems.
Superstructure6 SatisfactoryStructural elements show some minor deterioration.
Substructure7 GoodSome minor problems.
Last inspectionMay 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourBridge not over waterway
Structural evaluation6: Equal to present minimum criteria
Deck geometry5: Somewhat better than minimum adequacy to tolerate being left in place as is
Approach roadway alignment6: Equal to present minimum criteria
Operating rating40.7 US tons
Inventory rating31.4 US tons

Structure

Structure typeBox Beam or Girders - Multiple
MaterialConcrete Continuous
DeckConcrete, cast-in-place
Main spans3
Design loadHS 20
Structure length148 ft (45.1 m)
Longest span98 ft (29.9 m)
Deck width71 ft (21.7 m)
Roadway width68 ft (20.7 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic45,000 (2016)
Projected traffic42,000 by 2036
Trucks12%
Lanes on structure5
Traffic directionOne-way traffic
CarriesHighway
CrossesHighway
Detour if closed—
TollOn a free road
National Highway SystemYes

Ownership and planned work

OwnerOther Local Agency
Maintained byOther Local Agency
Historic statusHistorical significance not determinable at this time
Work proposedReplacement because of substandard load-carrying capacity or roadway geometry
Estimated improvement cost$11.1 million (2022 estimate)
NavigationNot applicable (no waterway)

Frequently asked questions

When was SB Airport Expy over S 170th ST built?

It was built in 1972, making it 53 years old in 2025.

What condition is SB Airport Expy over S 170th ST 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 May 2023.

How much traffic does SB Airport Expy over S 170th ST carry?

About 45,000 vehicles per day (2016 count), of which roughly 12% are trucks.

How long is SB Airport Expy over S 170th ST?

The structure is 148 ft (45.1 m) long with a longest span of 98 ft (29.9 m) and a deck 71 ft wide.

Who owns SB Airport Expy over S 170th ST?

It is owned by the Other Local Agency.