US Bridges

SR 9 over Thunder Creek

Fair

Skagit County, Washington · 6.3 N JCT SR 20 · Structure no. 0003349A0000000

Built
1900
125 years old, rebuilt 1947
Condition
Fair
inspected April 2023
Type
Tee Beam
Concrete
Length
31 ft
1 main span
Daily traffic
3,684
2023 count
Owner
State
State Highway Agency

About this bridge

SR 9 over Thunder Creek is a concrete tee beam carrying SR 9 over Thunder Creek in Skagit County, Washington. It was built in 1900 and reconstructed in 1947, so it is 125 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 3,684 vehicles a day, roughly 12% of them trucks, projected to reach 5,383 by 2039. The structure is 31 ft (9.4 m) long and 29 ft wide. If it were closed, the detour would be 3.1 mi (5 km).

Location

Open in Google Maps
CarriesSR 9
CrossesThunder Creek
Location6.3 N JCT SR 20
RouteState Highway 9
CountySkagit County
StateWashington
Coordinates48.59978, -122.23192
Functional classRural Major Collector

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 protection8 Very GoodNo problems noted.
Last inspectionApril 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourCountermeasures installed to correct a previously existing problem
Structural evaluation4: Meets minimum tolerable limits to be left in place as is
Deck geometry2: Basically intolerable, requiring high priority of replacement
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating22.2 US tons
Inventory rating17.2 US tons

Structure

Structure typeTee Beam
MaterialConcrete
DeckConcrete, cast-in-place
Main spans1
Design loadHS 15
Structure length31 ft (9.4 m)
Longest span30 ft (9.1 m)
Deck width29 ft (8.7 m)
Roadway width24 ft (7.3 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic3,684 (2023)
Projected traffic5,383 by 2039
Trucks12%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed3.1 mi (5 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$383,000 (2022 estimate)
NavigationNo navigation control on waterway

Frequently asked questions

When was SR 9 over Thunder Creek built?

It was built in 1900, making it 125 years old in 2025. It was reconstructed in 1947.

What condition is SR 9 over Thunder Creek 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 2023.

How much traffic does SR 9 over Thunder Creek carry?

About 3,684 vehicles per day (2023 count), of which roughly 12% are trucks.

How long is SR 9 over Thunder Creek?

The structure is 31 ft (9.4 m) long with a longest span of 30 ft (9.1 m) and a deck 29 ft wide.

Who owns SR 9 over Thunder Creek?

It is owned by the State Highway Agency.