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
- Old Mil. RR Grade over Slough Bridge in Shoshone County, Idaho, is rated in poor condition in the 2025 National Bridge Inventory (as of ).
- 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.
- Its traffic status in the 2025 inventory is posted for load (NBI item 41).
- Its condition class and component ratings are unchanged from the 2024 inventory.
- Its most recent inspection on record is dated August 2024, on a 12-month routine inspection cycle.
- 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.
View this bridge on a map → (47.29733, -116.26203)
Component ratings
| Component | Rating (2024) | Rating (2025) | FHWA scale meaning |
|---|---|---|---|
| Deck | 4 | 4 | Poor condition |
| Superstructure | 6 | 6 | Satisfactory condition |
| Substructure | 4 | 4 | Poor condition |
Bridge details
| Structure | Timber stringer or multi-beam girder |
| Length | about 97 ft |
| Location | 1.4N 3.1W Calder |
| NBI structure number | 000000000037080 |
| Condition class | Poor |
| Traffic status (item 41) | Posted for load |
| Last inspection (item 90) | August 2024 |
| Inspection interval (item 91) | 12 months |
| Scour (item 113) | 5: foundations stable, scour within the limits of the footing or piles |
Source: FHWA National Bridge Inventory, 2025 data as reported by the Idaho department of transportation.
Busiest bridges in Shoshone County
| 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 |
All bridges nearby: Shoshone County, ID bridge conditions · every bridge in Shoshone County · Idaho bridges.
Background: how bridge ratings work · what "poor" and "structurally deficient" actually mean · how often bridges are inspected.