US Bridges

Diablo Dam RD over Diablo Gorge

Fair

King County, Washington · Diablo Access Road · Structure no. 087462000000000

Built
1962
63 years old
Condition
Fair
inspected August 2022
Type
Girder and Floorbeam System
Steel
Length
45 ft
1 main span
Daily traffic
580
2022 count
Owner
Local
Other Local Agency

About this bridge

Diablo Dam RD over Diablo Gorge is a steel girder and floorbeam system carrying Diablo Dam RD over Diablo Gorge in King County, Washington. It was built in 1962, so it is 63 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 580 vehicles a day, roughly 15% of them trucks, projected to reach 620 by 2042. The structure is 45 ft (13.7 m) long and 20 ft wide.

Location

Open in Google Maps
CarriesDiablo Dam RD
CrossesDiablo Gorge
LocationDiablo Access Road
CountyKing County
StateWashington
Coordinates48.71231, -121.13392
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
Deck6 SatisfactoryStructural elements show some minor deterioration.
Superstructure6 SatisfactoryStructural elements show some minor deterioration.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Last inspectionAugust 2022
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourBridge not over waterway
Structural evaluation6: Equal to present minimum criteria
Deck geometry2: Basically intolerable, requiring high priority of replacement
Approach roadway alignment8: Equal to present desirable criteria
Operating rating99 US tons
Inventory rating71 US tons

Structure

Structure typeGirder and Floorbeam System
MaterialSteel
DeckConcrete, precast panels
Main spans1
Design loadUnknown
Structure length45 ft (13.7 m)
Longest span44 ft (13.4 m)
Deck width20 ft (6 m)
Roadway width18 ft (5.5 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic580 (2022)
Projected traffic620 by 2042
Trucks15%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesOther
Detour if closed—
TollOn a free road
National Highway SystemNo

Ownership and planned work

OwnerOther Local Agency
Maintained byOther Local Agency
Historic statusHistorical significance not determinable at this time
Work proposedReplacement because of substandard load-carrying capacity or roadway geometry
Estimated improvement cost$2 million (2022 estimate)
NavigationNot applicable (no waterway)

Frequently asked questions

When was Diablo Dam RD over Diablo Gorge built?

It was built in 1962, making it 63 years old in 2025.

What condition is Diablo Dam RD over Diablo Gorge 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 2022.

How much traffic does Diablo Dam RD over Diablo Gorge carry?

About 580 vehicles per day (2022 count), of which roughly 15% are trucks.

How long is Diablo Dam RD over Diablo Gorge?

The structure is 45 ft (13.7 m) long with a longest span of 44 ft (13.4 m) and a deck 20 ft wide.

Who owns Diablo Dam RD over Diablo Gorge?

It is owned by the Other Local Agency.