US Bridges

US 12 over Overflow Channel

Good

Thurston County, Washington · 0.4 E Grays Hbr CO · Structure no. 0012104A0000000

Built
1981
44 years old
Condition
Good
inspected April 2024
Type
Slab
Prestressed Concrete
Length
138 ft
4 main spans
Daily traffic
8,498
2023 count
Owner
State
State Highway Agency

About this bridge

US 12 over Overflow Channel is a prestressed concrete slab carrying US 12 over Overflow Channel in Thurston County, Washington. It was built in 1981, so it is 44 years old, younger than the Washington average of 49.8 years.

The most recent inspection reported to the Federal Highway Administration rates it in good condition with a lowest component rating of 7 out of 9. All primary components (deck, superstructure, substructure, or culvert) are rated 7 or higher. No significant problems were noted.

It carries about 8,498 vehicles a day, roughly 17% of them trucks, projected to reach 12,276 by 2039. The structure is 138 ft (42.1 m) long and 41 ft wide. If it were closed, the detour would be 3.1 mi (5 km).

Location

Open in Google Maps
CarriesUS 12
CrossesOverflow Channel
Location0.4 E Grays Hbr CO
RouteU.S. Route 12
CountyThurston County
StateWashington
Coordinates46.82664, -123.15249
Functional classRural Principal Arterial - Other

Condition and inspection

Good

All primary components (deck, superstructure, substructure, or culvert) are rated 7 or higher. No significant problems were noted.

ComponentRatingMeaning
Deck8 Very GoodNo problems noted.
Superstructure7 GoodSome minor problems.
Substructure7 GoodSome minor problems.
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 evaluation7: Better than present minimum criteria
Deck geometry5: Somewhat better than minimum adequacy to tolerate being left in place as is
Waterway adequacy3: Basically intolerable, requiring high priority of corrective action
Approach roadway alignment8: Equal to present desirable criteria
Operating rating60 US tons
Inventory rating36 US tons

Structure

Structure typeSlab
MaterialPrestressed Concrete
DeckConcrete, precast panels
Main spans4
Design loadHS 20
Structure length138 ft (42.1 m)
Longest span34 ft (10.4 m)
Deck width41 ft (12.5 m)
Roadway width38 ft (11.6 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic8,498 (2023)
Projected traffic12,276 by 2039
Trucks17%
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$2.5 million (2022 estimate)
NavigationNo navigation control on waterway

Frequently asked questions

When was US 12 over Overflow Channel built?

It was built in 1981, making it 44 years old in 2025.

What condition is US 12 over Overflow Channel in?

The National Bridge Inventory rates it in good condition. All primary components (deck, superstructure, substructure, or culvert) are rated 7 or higher. No significant problems were noted. The last reported inspection was in April 2024.

How much traffic does US 12 over Overflow Channel carry?

About 8,498 vehicles per day (2023 count), of which roughly 17% are trucks.

How long is US 12 over Overflow Channel?

The structure is 138 ft (42.1 m) long with a longest span of 34 ft (10.4 m) and a deck 41 ft wide.

Who owns US 12 over Overflow Channel?

It is owned by the State Highway Agency.