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Co Road 451 over N Br Thunder Bay River

Montmorency County, Michigan · rated Fair in the 2025 National Bridge Inventory

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

Co Road 451 over N Br Thunder Bay River in Montmorency County, Michigan, 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 1994, making it 31 years old at the 2025 inventory.
It carries about 2,126 vehicles a day (traffic count year 2021).
Its listed owner is the county highway agency.
It is one of 8 of the 21 inventoried bridges in Montmorency County rated fair (38.1%); 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	Prestressed concrete multiple box beam
Length	about 57 ft
Location	Sec 1 Montmorency Twp E
NBI structure number	000000000007546
Condition class	Fair

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

Bridge	Built	Vehicles/day	Condition
M-32 Bs\|s State St over Thunder Bay River	2009	6,400	Fair
M-32 over Miller Creek	1991	4,572	Fair
M-32 over Thunder Bay River	1927	4,572	Fair
M-33 over Gilchrist Creek	1951	1,647	Fair
M-33 over Thunder Bay River	1968	1,647	Fair
Airport Road over Thunder Bay River	1969	160	Good