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Old Hwy 312 over Yellowstone River 170

Yellowstone County, Montana · rated Poor in the 2025 National Bridge Inventory

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

Old Hwy 312 over Yellowstone River 170 in Yellowstone County, Montana, is rated in poor condition in the 2025 National Bridge Inventory (as of August 20, 2026).
Its lowest-rated component is the deck, rated 4 (poor condition) on the 0-9 scale.
It was built in 1949, making it 76 years old at the 2025 inventory.
It carries about 4,005 vehicles a day (traffic count year 2023).
Its listed owner is the state highway agency.
It is one of 7 of the 290 inventoried bridges in Yellowstone County rated poor (2.4%); 7 (2.4%) are rated poor.
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.

Component ratings


Structure	Continuous steel girder and floorbeam
Length	about 1,021 ft
Location	Huntley
NBI structure number	L56788012+07001
Condition class	Poor

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

Bridge	Built	Vehicles/day	Condition
I90 over MT Power RR Spur	2023	29,488	Good
I 90 over City County Drain Ditch	1966	27,985	Fair
King Ave W over Bbwa Canal	1994	26,602	Fair
Mullowney Ln over RR	2007	23,980	Good
Mullowney Ln over RR	2007	23,980	Fair
US 87 over Int Lockwood I 90	1966	23,199	Fair