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Old Mil. RR Grade over Slough Bridge

Shoshone County, Idaho · rated Poor in the 2025 National Bridge Inventory

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

Old Mil. RR Grade over Slough Bridge in Shoshone County, Idaho, 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 1912 and reconstructed in 1991, making it 113 years old at the 2025 inventory.
It carries about 15 vehicles a day (traffic count year 2023).
Its listed owner is the county highway agency.
It is one of 26 of the 261 inventoried bridges in Shoshone County rated poor (10.0%); 26 (10.0%) 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	Timber stringer or multi-beam girder
Length	about 97 ft
Location	1.4N 3.1W Calder
NBI structure number	000000000037080
Condition class	Poor

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

Bridge	Built	Vehicles/day	Condition
I 90 over Stc 5766;SILVERTON Ic	1978	11,000	Fair
I 90 EB & WB over S.fk.cda R;fr.rd.	1978	11,000	Fair
I 90 over S.fk.coeur Dalene River	1987	11,000	Fair
I 90 Ebl & Wbl over Crossroad Bd;w.wallace I	1987	11,000	Fair
I 90 over I 90B;CANYON CR	1991	11,000	Fair
I 90 Spur over Canyon Creek	1940	10,500	Fair