US Bridges

I-5 over SR 18

Fair

King County, Washington · 2.5 N Pierce CO · Structure no. 0006078A0000000

Built
1959
66 years old
Condition
Fair
inspected July 2023
Type
Stringer/Multi-beam or Girder
Prestressed Concrete
Length
206 ft
4 main spans
Daily traffic
70,133
2023 count
Owner
State
State Highway Agency

About this bridge

I-5 over SR 18 is a prestressed concrete stringer/multi-beam or girder carrying I-5 over SR 18 in King County, Washington. It was built in 1959, 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 5 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 70,133 vehicles a day, roughly 7% of them trucks, projected to reach 100,667 by 2039. The structure is 206 ft (62.8 m) long and 102 ft wide. If it were closed, the detour would be 1.2 mi (2 km).

Location

Open in Google Maps
CarriesI-5
CrossesSR 18
Location2.5 N Pierce CO
RouteInterstate 5
CountyKing County
StateWashington
Coordinates47.28936, -122.30644
Functional classUrban Principal Arterial - Interstate

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.
Superstructure5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Substructure7 GoodSome minor problems.
Last inspectionJuly 2023
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 geometry9: Superior to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating81 US tons
Inventory rating48.9 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialPrestressed Concrete
DeckConcrete, cast-in-place
Main spans4
Design loadHS 20
Structure length206 ft (62.8 m)
Longest span65 ft (19.8 m)
Deck width102 ft (31 m)
Roadway width100 ft (30.5 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic70,133 (2023)
Projected traffic100,667 by 2039
Trucks7%
Lanes on structure6
Traffic directionOne-way traffic
CarriesHighway
CrossesHighway
Detour if closed1.2 mi (2 km)
TollOn a free road
National Highway SystemYes
Strategic Highway NetworkInterstate STRAHNET route

Ownership and planned work

OwnerState Highway Agency
Maintained byState Highway Agency
Historic statusNot eligible for the National Register of Historic Places
Work proposedRehabilitation because of general structure deterioration or inadequate strength
Estimated improvement cost$10 million (2022 estimate)
NavigationNot applicable (no waterway)

Frequently asked questions

When was I-5 over SR 18 built?

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

What condition is I-5 over SR 18 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 July 2023.

How much traffic does I-5 over SR 18 carry?

About 70,133 vehicles per day (2023 count), of which roughly 7% are trucks.

How long is I-5 over SR 18?

The structure is 206 ft (62.8 m) long with a longest span of 65 ft (19.8 m) and a deck 102 ft wide.

Who owns I-5 over SR 18?

It is owned by the State Highway Agency.