SR 99 over Lake Union

King County, Washington · rated Fair in the 2025 National Bridge Inventory

United States Bridge Conditions2025 National Bridge Inventory, FHWACompiled August 20, 2026

• SR 99 over Lake Union in King County, Washington, is rated in fair condition in the 2025 National Bridge Inventory (as of August 20, 2026).
• Its lowest-rated component is the superstructure, rated 5 (fair condition) on the 0-9 scale.
• It was built in 1931, making it 94 years old at the 2025 inventory.
• It carries about 61,259 vehicles a day (traffic count year 2023).
• Its listed owner is the state highway agency.
• It is one of 607 of the 1,252 inventoried bridges in King County rated fair (48.5%); 50 (4.0%) are rated poor.
• Its traffic status in the 2025 inventory is open, no restriction (NBI item 41).
• Its condition class and component ratings are unchanged from the 2024 inventory.
• Its most recent inspection on record is dated August 2023, on a 24-month routine inspection cycle.
• It has fracture-critical members (NBI item 92A): steel tension members without a redundant load path, which get their own scheduled inspections.
• A fair rating means the lowest-rated major component scores 5 or 6 on FHWA's 0-9 scale: some deterioration or minor section loss, but the structure is sound. It is the middle class, not a warning.

View this bridge on a map → (47.64317, -122.34719)

Component ratings

Bridge details

Source: FHWA National Bridge Inventory, 2025 data as reported by the Washington department of transportation.

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Background: how bridge ratings work · what "poor" and "structurally deficient" actually mean · how often bridges are inspected.