US Bridges

I-5 over Nisqually Overflow-South

Fair

Thurston County, Washington · 2.7 N JCT SR 510 · Structure no. 0012137A0000000

Built
1982
43 years old
Condition
Fair
inspected November 2023
Type
Stringer/Multi-beam or Girder
Prestressed Concrete Continuous
Length
200 ft
2 main spans
Daily traffic
50,433
2023 count
Owner
State
State Highway Agency

About this bridge

I-5 over Nisqually Overflow-South is a prestressed concrete continuous stringer/multi-beam or girder carrying I-5 over Nisqually Overflow-South in Thurston County, Washington. It was built in 1982, so it is 43 years old, younger 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 50,433 vehicles a day, roughly 11% of them trucks, projected to reach 74,353 by 2039. The structure is 200 ft (61 m) long and 60 ft wide. If it were closed, the detour would be 3.7 mi (6 km).

Location

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CarriesI-5
CrossesNisqually Overflow-South
Location2.7 N JCT SR 510
RouteInterstate 5
CountyThurston County
StateWashington
Coordinates47.06883, -122.71097
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.
Superstructure7 GoodSome minor problems.
Substructure7 GoodSome minor problems.
Channel and channel protection8 Very GoodNo problems noted.
Last inspectionNovember 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour within limits of footing or piles
Structural evaluation7: Better than present minimum criteria
Deck geometry7: Better than present minimum criteria
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating47.5 US tons
Inventory rating36.8 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialPrestressed Concrete Continuous
DeckConcrete, cast-in-place
Main spans2
Design loadHS 20 + Mod
Structure length200 ft (61 m)
Longest span100 ft (30.5 m)
Deck width60 ft (18.3 m)
Roadway width58 ft (17.6 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic50,433 (2023)
Projected traffic74,353 by 2039
Trucks11%
Lanes on structure3
Traffic directionOne-way traffic
CarriesHighway
CrossesWaterway
Detour if closed3.7 mi (6 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$6 million (2022 estimate)
NavigationNo navigation control on waterway

Frequently asked questions

When was I-5 over Nisqually Overflow-South built?

It was built in 1982, making it 43 years old in 2025.

What condition is I-5 over Nisqually Overflow-South 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 November 2023.

How much traffic does I-5 over Nisqually Overflow-South carry?

About 50,433 vehicles per day (2023 count), of which roughly 11% are trucks.

How long is I-5 over Nisqually Overflow-South?

The structure is 200 ft (61 m) long with a longest span of 100 ft (30.5 m) and a deck 60 ft wide.

Who owns I-5 over Nisqually Overflow-South?

It is owned by the State Highway Agency.