US Bridges

SR 31 over Slate Creek

Fair

Pend Oreille County, Washington · 21.1 N JCT SR 20 · Structure no. 0001745A0000000

Built
1933
92 years old
Condition
Fair
inspected August 2024
Type
Girder and Floorbeam System
Steel
Length
216 ft
1 main span
Daily traffic
146
2023 count
Owner
State
State Highway Agency

About this bridge

SR 31 over Slate Creek is a steel girder and floorbeam system carrying SR 31 over Slate Creek in Pend Oreille County, Washington. It was built in 1933, so it is 92 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 5 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 146 vehicles a day, roughly 18% of them trucks, projected to reach 358 by 2039. The structure is 216 ft (65.8 m) long and 30 ft wide. If it were closed, the detour would be 98.8 mi (159 km).

Location

Open in Google Maps
CarriesSR 31
CrossesSlate Creek
Location21.1 N JCT SR 20
RouteState Highway 31
CountyPend Oreille County
StateWashington
Coordinates48.92919, -117.30709
Functional classRural Minor Arterial

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.
Substructure5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Channel and channel protection8 Very GoodNo problems noted.
Last inspectionAugust 2024
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour above top of footing
Structural evaluation5: Somewhat better than minimum adequacy to tolerate being left in place as is
Deck geometry5: Somewhat better than minimum adequacy to tolerate being left in place as is
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment6: Equal to present minimum criteria
Operating rating41 US tons
Inventory rating25 US tons

Structure

Structure typeGirder and Floorbeam System
MaterialSteel
DeckConcrete, cast-in-place
Main spans1 (+4 approach)
Design loadH 15
Structure length216 ft (65.8 m)
Longest span80 ft (24.4 m)
Deck width30 ft (9.2 m)
Roadway width27 ft (8.2 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic146 (2023)
Projected traffic358 by 2039
Trucks18%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed98.8 mi (159 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$2.9 million (2022 estimate)
NavigationNo navigation control on waterway

Frequently asked questions

When was SR 31 over Slate Creek built?

It was built in 1933, making it 92 years old in 2025.

What condition is SR 31 over Slate 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 August 2024.

How much traffic does SR 31 over Slate Creek carry?

About 146 vehicles per day (2023 count), of which roughly 18% are trucks.

How long is SR 31 over Slate Creek?

The structure is 216 ft (65.8 m) long with a longest span of 80 ft (24.4 m) and a deck 30 ft wide.

Who owns SR 31 over Slate Creek?

It is owned by the State Highway Agency.