SH 21 over Clear Creek;at Lowman
Boise County, Idaho · rated Fair in the 2025 National Bridge Inventory
United States Bridge Conditions2025 National Bridge Inventory, FHWACompiled
- SH 21 over Clear Creek;at Lowman in Boise County, Idaho, is rated in fair condition in the 2025 National Bridge Inventory (as of ).
- Its lowest-rated component is the substructure, rated 5 (fair condition) on the 0-9 scale.
- It was built in 1939, making it 86 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 39 of the 89 inventoried bridges in Boise County rated fair (43.8%); 5 (5.6%) are rated poor.
- Its traffic status in the 2025 inventory is open, no restriction (NBI item 41).
- Its class is unchanged from 2024 (fair), but component ratings moved: deck 5 to 6, superstructure 5 to 6.
- Its most recent inspection on record is dated October 2024, on a 24-month routine inspection cycle.
- It is coded scour critical (NBI item 113 = 3): scour critical: foundations unstable for the assessed or calculated scour.
- 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.
View this bridge on a map → (44.08248, -115.61271)
Component ratings
| Component | Rating (2024) | Rating (2025) | FHWA scale meaning |
|---|---|---|---|
| Deck | 5 | 6 | Satisfactory condition |
| Superstructure | 5 | 6 | Satisfactory condition |
| Substructure | 5 | 5 | Fair condition |
Bridge details
| Structure | Continuous steel stringer or multi-beam girder |
| Length | about 149 ft |
| Location | at Lowman |
| NBI structure number | 000000000012890 |
| Condition class | Fair |
| Traffic status (item 41) | Open, no restriction |
| Last inspection (item 90) | October 2024 |
| Inspection interval (item 91) | 24 months |
| Scour (item 113) | 3: scour critical: foundations unstable for the assessed or calculated scour |
Source: FHWA National Bridge Inventory, 2025 data as reported by the Idaho department of transportation.
Busiest bridges in Boise County
| 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 |
All bridges nearby: Boise County, ID bridge conditions · every bridge in Boise County · Idaho bridges.
Background: how bridge ratings work · what "poor" and "structurally deficient" actually mean · how often bridges are inspected.