US Bridges

Mountain Loop HWY over S.F. Stillaguamish River

Fair

Snohomish County, Washington · 1.8 NE JCT SR 92 · Structure no. 080625000000000

Built
1934
91 years old
Condition
Fair
inspected June 2024
Type
Arch - Deck
Steel
Length
340 ft
1 main span
Daily traffic
6,285
2021 count
Owner
County
County Highway Agency

About this bridge

Mountain Loop HWY over S.F. Stillaguamish River is a steel arch - deck carrying Mountain Loop HWY over S.F. Stillaguamish River in Snohomish County, Washington. It was built in 1934, so it is 91 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 6,285 vehicles a day, roughly 13% of them trucks, projected to reach 10,000 by 2044. The structure is 340 ft (103.6 m) long and 29 ft wide. If it were closed, the detour would be 93.8 mi (151 km).

Location

Open in Google Maps
CarriesMountain Loop HWY
CrossesS.F. Stillaguamish River
Location1.8 NE JCT SR 92
RouteCounty Highway 98960
CountySnohomish County
StateWashington
Coordinates48.10253, -121.95358
Functional classUrban 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
Deck6 SatisfactoryStructural elements show some minor deterioration.
Superstructure6 SatisfactoryStructural elements show some minor deterioration.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Channel and channel protection8 Very GoodNo problems noted.
Last inspectionJune 2024
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations on dry land well above flood water elevations
Structural evaluation6: Equal to present minimum criteria
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 rating66 US tons
Inventory rating40 US tons

Structure

Structure typeArch - Deck
MaterialSteel
DeckConcrete, cast-in-place
Main spans1 (+5 approach)
Design loadH 15
Structure length340 ft (103.6 m)
Longest span160 ft (48.8 m)
Deck width29 ft (8.7 m)
Roadway width20 ft (6.1 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic6,285 (2021)
Projected traffic10,000 by 2044
Trucks13%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway and pedestrian
CrossesWaterway
Detour if closed93.8 mi (151 km)
TollOn a free road
National Highway SystemNo

Ownership and planned work

OwnerCounty Highway Agency
Maintained byCounty Highway Agency
Historic statusNot eligible for the National Register of Historic Places
Work proposedReplacement because of substandard load-carrying capacity or roadway geometry
Estimated improvement cost$12.6 million (2022 estimate)
NavigationNo navigation control on waterway

Frequently asked questions

When was Mountain Loop HWY over S.F. Stillaguamish River built?

It was built in 1934, making it 91 years old in 2025.

What condition is Mountain Loop HWY over S.F. Stillaguamish River 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 2024.

How much traffic does Mountain Loop HWY over S.F. Stillaguamish River carry?

About 6,285 vehicles per day (2021 count), of which roughly 13% are trucks.

How long is Mountain Loop HWY over S.F. Stillaguamish River?

The structure is 340 ft (103.6 m) long with a longest span of 160 ft (48.8 m) and a deck 29 ft wide.

Who owns Mountain Loop HWY over S.F. Stillaguamish River?

It is owned by the County Highway Agency.