US Bridges

US 12 over Slough

Fair

Thurston County, Washington · 1.5 E Grays Hbr CO · Structure no. 0001000A0000000

Built
1926
99 years old, rebuilt 1983
Condition
Fair
inspected April 2024
Type
Tee Beam
Concrete
Length
45 ft
1 main span
Daily traffic
10,063
2023 count
Owner
State
State Highway Agency

About this bridge

US 12 over Slough is a concrete tee beam carrying US 12 over Slough in Thurston County, Washington. It was built in 1926 and reconstructed in 1983, so it is 99 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 10,063 vehicles a day, roughly 14% of them trucks, projected to reach 14,456 by 2039. The structure is 45 ft (13.7 m) long and 39 ft wide. If it were closed, the detour would be 3.1 mi (5 km).

Location

Open in Google Maps
CarriesUS 12
CrossesSlough
Location1.5 E Grays Hbr CO
RouteU.S. Route 12
CountyThurston County
StateWashington
Coordinates46.82519, -123.12972
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 protection7 GoodSome minor problems.
Last inspectionApril 2024
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour within limits of footing or piles
Structural evaluation6: Equal to present minimum criteria
Deck geometry4: Meets minimum tolerable limits to be left in place as is
Waterway adequacy3: Basically intolerable, requiring high priority of corrective action
Approach roadway alignment8: Equal to present desirable criteria
Operating rating39.2 US tons
Inventory rating30.3 US tons

Structure

Structure typeTee Beam
MaterialConcrete
DeckConcrete, cast-in-place
Main spans1
Design loadH 15
Structure length45 ft (13.7 m)
Longest span45 ft (13.7 m)
Deck width39 ft (11.9 m)
Roadway width36 ft (11 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic10,063 (2023)
Projected traffic14,456 by 2039
Trucks14%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed3.1 mi (5 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$812,000 (2022 estimate)
NavigationNo navigation control on waterway

Frequently asked questions

When was US 12 over Slough built?

It was built in 1926, making it 99 years old in 2025. It was reconstructed in 1983.

What condition is US 12 over Slough 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 April 2024.

How much traffic does US 12 over Slough carry?

About 10,063 vehicles per day (2023 count), of which roughly 14% are trucks.

How long is US 12 over Slough?

The structure is 45 ft (13.7 m) long with a longest span of 45 ft (13.7 m) and a deck 39 ft wide.

Who owns US 12 over Slough?

It is owned by the State Highway Agency.