US Bridges

S 129th ST over I-5

PoorPosted for load

King County, Washington · 0.5 N JCT SR 599 · Structure no. 0007843A0000000

Built
1966
59 years old
Condition
Poor
inspected May 2024
Type
Stringer/Multi-beam or Girder
Steel Continuous
Length
930 ft
6 main spans
Daily traffic
6,386
2017 count
Owner
State
State Highway Agency

About this bridge

S 129th ST over I-5 is a steel continuous stringer/multi-beam or girder carrying S 129th ST over I-5 in King County, Washington. It was built in 1966, so it is 59 years old, older than the Washington average of 49.8 years.

The most recent inspection reported to the Federal Highway Administration rates it in poor condition with a lowest component rating of 4 out of 9. The lowest-rated primary component is rated 4 or below, indicating advanced deterioration. Poor does not mean unsafe; such bridges are inspected more often and may carry load restrictions. Its operating status is: posted for load restriction.

It carries about 6,386 vehicles a day, roughly 1% of them trucks, projected to reach 9,336 by 2038. The structure is 930 ft (283.5 m) long and 33 ft wide. If it were closed, the detour would be 5 mi (8 km).

Location

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CarriesS 129th ST
CrossesI-5
Location0.5 N JCT SR 599
RouteCity Street 0
CountyKing County
StateWashington
Coordinates47.48906, -122.26406
Functional classUrban Collector

Condition and inspection

Poor

The lowest-rated primary component is rated 4 or below, indicating advanced deterioration. Poor does not mean unsafe; such bridges are inspected more often and may carry load restrictions.

ComponentRatingMeaning
Deck7 GoodSome minor problems.
Superstructure4 PoorAdvanced section loss, deterioration, spalling or scour.
Substructure4 PoorAdvanced section loss, deterioration, spalling or scour.
Last inspectionMay 2024
Inspection intervalevery 24 months
Operating statusPosted for load restriction
ScourBridge not over waterway
Structural evaluation3: Basically intolerable, requiring high priority of corrective action
Deck geometry3: Basically intolerable, requiring high priority of corrective action
Approach roadway alignment8: Equal to present desirable criteria
Operating rating20.9 US tons
Inventory rating14 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialSteel Continuous
DeckConcrete, cast-in-place
Main spans6 (+15 approach)
Design loadHS 15
Structure length930 ft (283.5 m)
Longest span155 ft (47.2 m)
Deck width33 ft (10.2 m)
Roadway width26 ft (7.9 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic6,386 (2017)
Projected traffic9,336 by 2038
Trucks1%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway and pedestrian
CrossesHighway and railroad
Detour if closed5 mi (8 km)
TollOn a free road
National Highway SystemNo

Ownership and planned work

OwnerState Highway Agency
Maintained byState Highway Agency
Historic statusHistorical significance not determinable at this time
Work proposedRehabilitation because of general structure deterioration or inadequate strength
Estimated improvement cost$15.9 million (2022 estimate)
NavigationNot applicable (no waterway)

Frequently asked questions

When was S 129th ST over I-5 built?

It was built in 1966, making it 59 years old in 2025.

What condition is S 129th ST over I-5 in?

The National Bridge Inventory rates it in poor condition. The lowest-rated primary component is rated 4 or below, indicating advanced deterioration. Poor does not mean unsafe; such bridges are inspected more often and may carry load restrictions. The last reported inspection was in May 2024.

How much traffic does S 129th ST over I-5 carry?

About 6,386 vehicles per day (2017 count), of which roughly 1% are trucks.

How long is S 129th ST over I-5?

The structure is 930 ft (283.5 m) long with a longest span of 155 ft (47.2 m) and a deck 33 ft wide.

Who owns S 129th ST over I-5?

It is owned by the State Highway Agency.