US Bridges

Thorp Prairie RD over I-90

Fair

Kittitas County, Washington · 3.9 E JCT SR 970 · Structure no. 0007574A0000000

Built
1965
60 years old
Condition
Fair
inspected August 2023
Type
Stringer/Multi-beam or Girder
Prestressed Concrete
Length
271 ft
4 main spans
Daily traffic
565
2012 count
Owner
State
State Highway Agency

About this bridge

Thorp Prairie RD over I-90 is a prestressed concrete stringer/multi-beam or girder carrying Thorp Prairie RD over I-90 in Kittitas County, Washington. It was built in 1965, so it is 60 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 565 vehicles a day, roughly 5% of them trucks, projected to reach 646 by 2036. The structure is 271 ft (82.6 m) long and 32 ft wide. If it were closed, the detour would be 9.9 mi (16 km).

Location

Open in Google Maps
CarriesThorp Prairie RD
CrossesI-90
Location3.9 E JCT SR 970
RouteCounty Highway 0
CountyKittitas County
StateWashington
Coordinates47.15797, -120.83378
Functional classRural Local

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.
Substructure7 GoodSome minor problems.
Last inspectionAugust 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourBridge not over waterway
Structural evaluation4: Meets minimum tolerable limits to be left in place as is
Deck geometry4: Meets minimum tolerable limits to be left in place as is
Approach roadway alignment6: Equal to present minimum criteria
Operating rating19.6 US tons
Inventory rating15 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialPrestressed Concrete
DeckConcrete, cast-in-place
Main spans4
Design loadHS 15
Structure length271 ft (82.6 m)
Longest span76 ft (23.2 m)
Deck width32 ft (9.8 m)
Roadway width24 ft (7.3 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic565 (2012)
Projected traffic646 by 2036
Trucks5%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway and pedestrian
CrossesHighway
Detour if closed9.9 mi (16 km)
TollOn a free road
National Highway SystemNo

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$3.9 million (2022 estimate)
NavigationNot applicable (no waterway)

Frequently asked questions

When was Thorp Prairie RD over I-90 built?

It was built in 1965, making it 60 years old in 2025.

What condition is Thorp Prairie RD over I-90 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 August 2023.

How much traffic does Thorp Prairie RD over I-90 carry?

About 565 vehicles per day (2012 count), of which roughly 5% are trucks.

How long is Thorp Prairie RD over I-90?

The structure is 271 ft (82.6 m) long with a longest span of 76 ft (23.2 m) and a deck 32 ft wide.

Who owns Thorp Prairie RD over I-90?

It is owned by the State Highway Agency.