56TH Ave So over Duwamish River
King County, Washington · rated Fair in the 2025 National Bridge Inventory
United States Bridge Conditions2025 National Bridge Inventory, FHWACompiled
- 56TH Ave So over Duwamish River in King County, Washington, is rated in fair condition in the 2025 National Bridge Inventory (as of ).
- Its lowest-rated component is the substructure, rated 6 (satisfactory condition) on the 0-9 scale.
- It was built in 1985, making it 40 years old at the 2025 inventory.
- It carries about 2,900 vehicles a day (traffic count year 2023).
- Its listed owner is a city or municipal 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.
- 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 → (47.4825, -122.26744)
Component ratings
| Component | Rating (2025) | FHWA scale meaning |
|---|---|---|
| Deck | 7 | Good condition |
| Superstructure | 7 | Good condition |
| Substructure | 6 | Satisfactory condition |
Bridge details
| Structure | Continuous concrete multiple box beam |
| Length | about 244 ft |
| Location | 0.1E Interurban Ave |
| NBI structure number | 081662000000000 |
| Condition class | Fair |
Source: FHWA National Bridge Inventory, 2025 data as reported by the Washington department of transportation.
Busiest bridges in King County
| Bridge | Built | Vehicles/day | Condition |
|---|---|---|---|
| I-90 EB over Sunset Creek | 2024 | 139,482 | Good |
| I-90 WB over Sunset Creek | 2024 | 139,482 | Good |
| N Queen Anne Dr over Ravine | 1935 | 125,000 | Fair |
| I-5 over Terrain | 1966 | 122,487 | Fair |
| SW Spokane St over Duwamish River W Waterwy | 1983 | 108,179 | Fair |
| I-5 over Terrain | 1966 | 106,282 | Fair |
All bridges nearby: King County, WA bridge conditions · every bridge in King County · Washington bridges.
Background: how bridge ratings work · what "poor" and "structurally deficient" actually mean · how often bridges are inspected.