I 15 over Sep Old US 91

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

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

• I 15 over Sep Old US 91 in Cascade County, Montana, 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 1961, making it 64 years old at the 2025 inventory.
• It carries about 2,218 vehicles a day (traffic count year 2023).
• Its listed owner is the state highway agency.
• It is one of 97 of the 185 inventoried bridges in Cascade County rated fair (52.4%); 11 (5.9%) are rated poor.
• Its traffic status in the 2025 inventory is open, no restriction (NBI item 41).
• Its condition class and component ratings are unchanged from the 2024 inventory.
• Its most recent inspection on record is dated June 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 → (47.23064, -111.75634)

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.