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SH 21 over Chapman Creek

Boise County, Idaho · rated Good in the 2025 National Bridge Inventory

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

SH 21 over Chapman Creek in Boise County, Idaho, is rated in good condition in the 2025 National Bridge Inventory (as of August 20, 2026).
Its lowest-rated component is the deck, rated 7 (good condition) on the 0-9 scale.
It was built in 1988, making it 37 years old at the 2025 inventory.
It carries about 1,200 vehicles a day (traffic count year 2023).
Its listed owner is the state highway agency.
It is one of 45 of the 89 inventoried bridges in Boise County rated good (50.6%); 5 (5.6%) are rated poor.
A good rating means every major component - deck, superstructure, substructure, or culvert - is rated 7 or higher on FHWA's 0-9 scale: no more than minor problems.

Component ratings


Structure	Prestressed concrete stringer or multi-beam girder
Length	about 169 ft
Location	18.7 NE. Lowman
NBI structure number	000000000012915
Condition class	Good

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

Bridge	Built	Vehicles/day	Condition
SH 55 over McLEOD WAY	2024	10,500	Good
SH 55 over Payette River	2021	8,800	Good
SH 55 over Power Canal	1994	8,800	Good
SH 55 over Uprr;horseshoe Bend Op	1971	7,800	Fair
SH 55 over Payette River	1971	7,800	Fair
SH 55 over S.fk.payette River	1955	7,300	Fair