421ST Avenue over Antelope Creek

Day County, South Dakota · rated Poor in the 2025 National Bridge Inventory

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

• 421ST Avenue over Antelope Creek in Day County, South Dakota, is rated in poor condition in the 2025 National Bridge Inventory (as of August 20, 2026).
• Its lowest-rated component is the substructure, rated 4 (poor condition) on the 0-9 scale.
• It was built in 1935, making it 90 years old at the 2025 inventory.
• It carries about 10 vehicles a day (traffic count year 2022).
• Its listed owner is the county highway agency.
• It is one of 9 of the 34 inventoried bridges in Day County rated poor (26.5%); 9 (26.5%) are rated poor.
• Its traffic status in the 2025 inventory is posted for load (NBI item 41).
• Its condition class and component ratings are unchanged from the 2024 inventory.
• Its most recent inspection on record is dated July 2024, 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 poor rating means at least one major component - deck, superstructure, or substructure - is rated 4 or lower on FHWA's 0-9 scale. It does not by itself mean the bridge is unsafe; bridges judged unsafe are closed or load-restricted by their owners.

View this bridge on a map → (45.57082, -97.79553)

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.