US Bridges

SR 20 Extension over Keystone Harbor

Fair

Island County, Washington · 3.4 W JCT SR 525 · Structure no. 0001697A0000000

Built
1979
46 years old
Condition
Fair
inspected June 2023
Type
Movable - Lift
Steel
Length
105 ft
2 main spans
Daily traffic
1,863
2010 count
Owner
State
State Highway Agency

About this bridge

SR 20 Extension over Keystone Harbor is a steel movable - lift carrying SR 20 Extension over Keystone Harbor in Island County, Washington. It was built in 1979, so it is 46 years old, younger 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 1,863 vehicles a day, roughly 2% of them trucks, projected to reach 3,268 by 2036. The structure is 105 ft (32 m) long and 24 ft wide. If it were closed, the detour would be 83.3 mi (134 km).

Location

Open in Google Maps
CarriesSR 20 Extension
CrossesKeystone Harbor
Location3.4 W JCT SR 525
RouteState Highway 20
CountyIsland County
StateWashington
Coordinates48.15936, -122.67272
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
Deck5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Superstructure5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Channel and channel protection8 Very GoodNo problems noted.
Last inspectionJune 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourScour critical; foundations unstable for calculated scour conditions
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 rating30 US tons
Inventory rating18 US tons

Structure

Structure typeMovable - Lift
MaterialSteel
DeckClosed grating
Main spans2
Design loadHS 20
Structure length105 ft (32 m)
Longest span100 ft (30.5 m)
Deck width24 ft (7.3 m)
Roadway width20 ft (6.1 m)
Vertical clearance over deck16 ft (4.9 m)

Traffic and service

Average daily traffic1,863 (2010)
Projected traffic3,268 by 2036
Trucks2%
Lanes on structure2
Traffic directionOne-way traffic
CarriesHighway and pedestrian
CrossesWaterway
Detour if closed83.3 mi (134 km)
TollToll bridge
National Highway SystemYes

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$1.2 million (2022 estimate)
NavigationNo navigation control on waterway

Frequently asked questions

When was SR 20 Extension over Keystone Harbor built?

It was built in 1979, making it 46 years old in 2025.

What condition is SR 20 Extension over Keystone Harbor 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 June 2023.

How much traffic does SR 20 Extension over Keystone Harbor carry?

About 1,863 vehicles per day (2010 count), of which roughly 2% are trucks.

How long is SR 20 Extension over Keystone Harbor?

The structure is 105 ft (32 m) long with a longest span of 100 ft (30.5 m) and a deck 24 ft wide.

Who owns SR 20 Extension over Keystone Harbor?

It is owned by the State Highway Agency.