US Bridges

US 101 over Lilliwaup R

Fair

Mason County, Washington · 12.6 S Jefferson CO · Structure no. 0000948A0000000

Built
1925
100 years old
Condition
Fair
inspected September 2023
Type
Tee Beam
Concrete
Length
111 ft
3 main spans
Daily traffic
3,173
2023 count
Owner
State
State Highway Agency

About this bridge

US 101 over Lilliwaup R is a concrete tee beam carrying US 101 over Lilliwaup R in Mason County, Washington. It was built in 1925, so it is 100 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 3,173 vehicles a day, roughly 13% of them trucks, projected to reach 4,356 by 2039. The structure is 111 ft (33.8 m) long and 27 ft wide. If it were closed, the detour would be 37.9 mi (61 km).

Location

Open in Google Maps
CarriesUS 101
CrossesLilliwaup R
Location12.6 S Jefferson CO
RouteU.S. Route 101
CountyMason County
StateWashington
Coordinates47.46344, -123.11428
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.
Superstructure7 GoodSome minor problems.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Channel and channel protection6 SatisfactoryStructural elements show some minor deterioration.
Last inspectionSeptember 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour within limits of footing or piles
Structural evaluation5: Somewhat better than minimum adequacy to tolerate being left in place as is
Deck geometry2: Basically intolerable, requiring high priority of replacement
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment6: Equal to present minimum criteria
Operating rating32.2 US tons
Inventory rating24.7 US tons

Structure

Structure typeTee Beam
MaterialConcrete
DeckConcrete, cast-in-place
Main spans3
Design loadUnknown
Structure length111 ft (33.8 m)
Longest span40 ft (12.2 m)
Deck width27 ft (8.3 m)
Roadway width24 ft (7.3 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic3,173 (2023)
Projected traffic4,356 by 2039
Trucks13%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed37.9 mi (61 km)
TollOn a free road
National Highway SystemYes

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$2.1 million (2022 estimate)
NavigationNo navigation control on waterway

Frequently asked questions

When was US 101 over Lilliwaup R built?

It was built in 1925, making it 100 years old in 2025.

What condition is US 101 over Lilliwaup R 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 September 2023.

How much traffic does US 101 over Lilliwaup R carry?

About 3,173 vehicles per day (2023 count), of which roughly 13% are trucks.

How long is US 101 over Lilliwaup R?

The structure is 111 ft (33.8 m) long with a longest span of 40 ft (12.2 m) and a deck 27 ft wide.

Who owns US 101 over Lilliwaup R?

It is owned by the State Highway Agency.