US Bridges

US 101 over Niawiakum River

Fair

Pacific County, Washington · 14.8 N JCT SR 4 · Structure no. 0013743A0000000

Built
1991
34 years old
Condition
Fair
inspected May 2023
Type
Stringer/Multi-beam or Girder
Prestressed Concrete Continuous
Length
1,375 ft
23 main spans
Daily traffic
3,145
2023 count
Owner
State
State Highway Agency

About this bridge

US 101 over Niawiakum River is a prestressed concrete continuous stringer/multi-beam or girder carrying US 101 over Niawiakum River in Pacific County, Washington. It was built in 1991, so it is 34 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 3,145 vehicles a day, roughly 11% of them trucks, projected to reach 3,712 by 2039. The structure is 1,375 ft (419.1 m) long and 39 ft wide. If it were closed, the detour would be 18 mi (29 km).

Location

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CarriesUS 101
CrossesNiawiakum River
Location14.8 N JCT SR 4
RouteU.S. Route 101
CountyPacific County
StateWashington
Coordinates46.62794, -123.92314
Functional classRural Principal Arterial - Other

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.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Channel and channel protection8 Very GoodNo problems noted.
Last inspectionMay 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour above top of footing
Structural evaluation6: Equal to present minimum criteria
Deck geometry5: Somewhat better than minimum adequacy to tolerate being left in place as is
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating69 US tons
Inventory rating41 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialPrestressed Concrete Continuous
DeckConcrete, cast-in-place
Main spans23
Design loadHS 20 + Mod
Structure length1,375 ft (419.1 m)
Longest span60 ft (18.3 m)
Deck width39 ft (11.9 m)
Roadway width36 ft (11 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic3,145 (2023)
Projected traffic3,712 by 2039
Trucks11%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed18 mi (29 km)
TollOn a free road
National Highway SystemYes
Strategic Highway NetworkNon-Interstate STRAHNET route

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$24.8 million (2022 estimate)
NavigationNavigation control on waterway (bridge permit required)

Frequently asked questions

When was US 101 over Niawiakum River built?

It was built in 1991, making it 34 years old in 2025.

What condition is US 101 over Niawiakum River 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 US 101 over Niawiakum River carry?

About 3,145 vehicles per day (2023 count), of which roughly 11% are trucks.

How long is US 101 over Niawiakum River?

The structure is 1,375 ft (419.1 m) long with a longest span of 60 ft (18.3 m) and a deck 39 ft wide.

Who owns US 101 over Niawiakum River?

It is owned by the State Highway Agency.