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US Highway 12 over Little Missouri River

Slope County, North Dakota · rated Fair in the 2025 National Bridge Inventory

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

US Highway 12 over Little Missouri River in Slope County, North Dakota, is rated in fair condition in the 2025 National Bridge Inventory (as of August 20, 2026).
Its lowest-rated component is the deck, rated 6 (satisfactory condition) on the 0-9 scale.
It was built in 1950 and reconstructed in 1987, making it 75 years old at the 2025 inventory.
It carries about 580 vehicles a day (traffic count year 2019).
Its listed owner is the state highway agency.
It is one of 7 of the 43 inventoried bridges in Slope County rated fair (16.3%); 0 (0.0%) are rated poor.
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.

Component ratings


Structure	Continuous steel stringer or multi-beam girder
Length	about 414 ft
Location	at Marmarth
NBI structure number	0012006555
Condition class	Fair

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

Bridge	Built	Vehicles/day	Condition
US Highway 85 over Creek	1991	1,080	Good
US Highway 85 over Branch-cannonball River	1963	1,010	Good
US Highway 85 over Philbrick Creek	1937	920	Good
US Highway 12 over Bnrr Separation	1984	561	Good
US Highway 12 over Little Beaver Creek	1987	520	Good
US Highway 12 over Branch of Beaver Creek	1950	510	Fair