US Bridges

US101 (hwy 9) over Half Viaduct

Fair

Tillamook County, Oregon · 023 MI N Manzanita · Structure no. 01951 009 04086

Built
1940
85 years old
Condition
Fair
inspected October 2024
Type
Tee Beam
Concrete Continuous
Length
375 ft
25 main spans
Daily traffic
5,743
2022 count
Owner
State
State Highway Agency

About this bridge

US101 (hwy 9) over Half Viaduct is a concrete continuous tee beam carrying US101 (hwy 9) over Half Viaduct in Tillamook County, Oregon. It was built in 1940, so it is 85 years old, older than the Oregon average of 49.9 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 5,743 vehicles a day, roughly 12% of them trucks, projected to reach 7,560 by 2042. The structure is 375 ft (114.3 m) long and 23 ft wide. If it were closed, the detour would be 6.2 mi (10 km).

Location

Open in Google Maps
CarriesUS101 (hwy 9)
CrossesHalf Viaduct
Location023 MI N Manzanita
RouteU.S. Route 101
CountyTillamook County
StateOregon
Coordinates45.74187, -123.9545
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
Deck8 Very GoodNo problems noted.
Superstructure8 Very GoodNo problems noted.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Last inspectionOctober 2024
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourBridge not over waterway
Structural evaluation5: Somewhat better than minimum adequacy to tolerate being left in place as is
Deck geometry4: Meets minimum tolerable limits to be left in place as is
Approach roadway alignment8: Equal to present desirable criteria
Operating rating29.7 US tons
Inventory rating22.8 US tons

Structure

Structure typeTee Beam
MaterialConcrete Continuous
DeckConcrete, cast-in-place
Main spans25
Design loadH 15
Structure length375 ft (114.3 m)
Longest span15 ft (4.6 m)
Deck width23 ft (6.9 m)
Roadway width29 ft (8.8 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic5,743 (2022)
Projected traffic7,560 by 2042
Trucks12%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesOther
Detour if closed6.2 mi (10 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 statusEligible for the National Register of Historic Places
Work proposedNone recorded
Estimated improvement cost—
NavigationNot applicable (no waterway)

Frequently asked questions

When was US101 (hwy 9) over Half Viaduct built?

It was built in 1940, making it 85 years old in 2025.

What condition is US101 (hwy 9) over Half Viaduct 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 October 2024.

How much traffic does US101 (hwy 9) over Half Viaduct carry?

About 5,743 vehicles per day (2022 count), of which roughly 12% are trucks.

How long is US101 (hwy 9) over Half Viaduct?

The structure is 375 ft (114.3 m) long with a longest span of 15 ft (4.6 m) and a deck 23 ft wide.

Who owns US101 (hwy 9) over Half Viaduct?

It is owned by the State Highway Agency.