US Bridges

NW Sammamish Road over Tributary 170

Good

King County, Washington · 0.5 M West of SR-900 · Structure no. 088029000000000

Built
2008
17 years old
Condition
Good
inspected September 2023
Type
Culvert
Concrete
Length
26 ft
1 main span
Daily traffic
13,500
2023 count
Owner
City
City or Municipal Highway Agency

About this bridge

NW Sammamish Road over Tributary 170 is a concrete culvert carrying NW Sammamish Road over Tributary 170 in King County, Washington. It was built in 2008, so it is 17 years old, younger than the Washington average of 49.8 years.

The most recent inspection reported to the Federal Highway Administration rates it in good condition with a lowest component rating of 8 out of 9. All primary components (deck, superstructure, substructure, or culvert) are rated 7 or higher. No significant problems were noted.

It carries about 13,500 vehicles a day, roughly 5% of them trucks, projected to reach 18,000 by 2043. The structure is 26 ft (7.9 m) long and 62 ft wide. If it were closed, the detour would be 5 mi (8 km).

Location

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CarriesNW Sammamish Road
CrossesTributary 170
Location0.5 M West of SR-900
RouteCity Street 590
CountyKing County
StateWashington
Coordinates47.55192, -122.06514
Functional classUrban Minor Arterial

Condition and inspection

Good

All primary components (deck, superstructure, substructure, or culvert) are rated 7 or higher. No significant problems were noted.

ComponentRatingMeaning
Channel and channel protection6 SatisfactoryStructural elements show some minor deterioration.
Culvert8 Very GoodNo problems noted.
Last inspectionSeptember 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour within limits of footing or piles
Structural evaluation8: Equal to present desirable criteria
Deck geometry4: Meets minimum tolerable limits to be left in place as is
Waterway adequacy7: Better than present minimum criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating106.8 US tons
Inventory rating89 US tons

Structure

Structure typeCulvert
MaterialConcrete
DeckNot applicable
Main spans1
Design loadHS 20 + Mod
Structure length26 ft (7.9 m)
Longest span26 ft (7.9 m)
Deck width62 ft (18.9 m)
Roadway width42 ft (12.8 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic13,500 (2023)
Projected traffic18,000 by 2043
Trucks5%
Lanes on structure3
Traffic directionTwo-way traffic
CarriesHighway and pedestrian
CrossesWaterway
Detour if closed5 mi (8 km)
TollOn a free road
National Highway SystemNo

Ownership and planned work

OwnerCity or Municipal Highway Agency
Maintained byCity or Municipal Highway Agency
Historic statusHistorical significance not determinable at this time
Work proposedWidening of existing bridge without deck rehabilitation
Estimated improvement cost$543,000 (2022 estimate)
NavigationNo navigation control on waterway

Frequently asked questions

When was NW Sammamish Road over Tributary 170 built?

It was built in 2008, making it 17 years old in 2025.

What condition is NW Sammamish Road over Tributary 170 in?

The National Bridge Inventory rates it in good condition. All primary components (deck, superstructure, substructure, or culvert) are rated 7 or higher. No significant problems were noted. The last reported inspection was in September 2023.

How much traffic does NW Sammamish Road over Tributary 170 carry?

About 13,500 vehicles per day (2023 count), of which roughly 5% are trucks.

How long is NW Sammamish Road over Tributary 170?

The structure is 26 ft (7.9 m) long with a longest span of 26 ft (7.9 m) and a deck 62 ft wide.

Who owns NW Sammamish Road over Tributary 170?

It is owned by the City or Municipal Highway Agency.