I090 W over 321 Ave

Lyman County, South Dakota · rated Fair in the 2025 National Bridge Inventory

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

• I090 W over 321 Ave in Lyman County, South Dakota, is rated in fair condition in the 2025 National Bridge Inventory (as of August 20, 2026).
• Its lowest-rated component is the substructure, rated 6 (satisfactory condition) on the 0-9 scale.
• It was built in 1971, making it 54 years old at the 2025 inventory.
• It carries about 3,852 vehicles a day (traffic count year 2024).
• Its listed owner is the state highway agency.
• It is one of 56 of the 114 inventoried bridges in Lyman County rated fair (49.1%); 12 (10.5%) are rated poor.
• Its traffic status in the 2025 inventory is open, no restriction (NBI item 41).
• Its class is unchanged from 2024 (fair), but component ratings moved: deck 6 to 7, superstructure 6 to 7.
• Its most recent inspection on record is dated March 2024, on a 24-month routine inspection cycle.
• 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 → (43.87622, -99.74063)

Component ratings

Bridge details

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

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