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Capitol Avenue over Swauger Slough

Custer County, Idaho · rated Fair in the 2025 National Bridge Inventory

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

Capitol Avenue over Swauger Slough in Custer County, Idaho, 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 1940 and reconstructed in 1999, making it 85 years old at the 2025 inventory.
It carries about 1,220 vehicles a day (traffic count year 2023).
Its listed owner is a city or municipal highway agency.
It is one of 72 of the 126 inventoried bridges in Custer County rated fair (57.1%); 14 (11.1%) 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	Steel stringer or multi-beam girder
Length	about 22 ft
Location	In Mackay
NBI structure number	000000000031815
Condition class	Fair

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

Bridge	Built	Vehicles/day	Condition
US 93 over Garden Creek	1941	2,300	Fair
SH 21 over Crooked Creek	1968	2,200	Fair
US 93 over Big Lost River	1987	1,500	Fair
US 93 over Challis Creek	1991	1,400	Good
US 93 over Salmon River;challis Br.	1995	1,400	Good
SH 75 over Redfish Lake Creek	1960	1,100	Fair