170TH St over Drainage

Plymouth County, Iowa · rated Poor in the 2025 National Bridge Inventory

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

• 170TH St over Drainage in Plymouth County, Iowa, 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 1900, making it 125 years old at the 2025 inventory.
• It carries about 34 vehicles a day (traffic count year 2022).
• Its listed owner is the county highway agency.
• It is one of 90 of the 430 inventoried bridges in Plymouth County rated poor (20.9%); 90 (20.9%) 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 12-month routine inspection cycle.
• It is coded scour critical (NBI item 113 = 3): scour critical: foundations unstable for the assessed or calculated scour.
• 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 → (42.80786, -96.30817)

Component ratings

Bridge details

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

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