18131: Maiden Rock over Big Hole River

Silver Bow County, Montana · rated Fair in the 2025 National Bridge Inventory

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

• 18131: Maiden Rock over Big Hole River in Silver Bow County, Montana, 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 1951 and reconstructed in 1993, making it 74 years old at the 2025 inventory.
• It carries about 25 vehicles a day (traffic count year 2022).
• It is one of 57 of the 70 inventoried bridges in Silver Bow County rated fair (81.4%); 2 (2.9%) 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.
• Status change: newly posted for load since 2024.
• Its most recent inspection on record is dated August 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 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 → (45.70152, -112.73534)

Component ratings

Bridge details

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

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