478TH Avenue over Six Mile Ck
Brookings County, South Dakota · rated Fair in the 2025 National Bridge Inventory
United States Bridge Conditions2025 National Bridge Inventory, FHWACompiled
- 478TH Avenue over Six Mile Ck in Brookings County, South Dakota, 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 1950, making it 75 years old at the 2025 inventory.
- It carries about 714 vehicles a day (traffic count year 2022).
- Its listed owner is the county highway agency.
- It is one of 115 of the 232 inventoried bridges in Brookings County rated fair (49.6%); 53 (22.8%) are rated poor.
- Its traffic status in the 2025 inventory is open, no restriction (NBI item 41).
- Its condition class and component ratings are unchanged from the 2024 inventory.
- Its most recent inspection on record is dated September 2023, 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 → (44.44134, -96.64615)
Component ratings
| Component | Rating (2024) | Rating (2025) | FHWA scale meaning |
|---|---|---|---|
| Deck | 6 | 6 | Satisfactory condition |
| Superstructure | 6 | 6 | Satisfactory condition |
| Substructure | 5 | 5 | Fair condition |
Bridge details
| Structure | Continuous concrete slab |
| Length | about 116 ft |
| Location | 0.5N White |
| NBI structure number | 000000006240070 |
| Condition class | Fair |
| Traffic status (item 41) | Open, no restriction |
| Last inspection (item 90) | September 2023 |
| 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 South Dakota department of transportation.
Busiest bridges in Brookings County
| Bridge | Built | Vehicles/day | Condition |
|---|---|---|---|
| I029 over Ck | 1966 | 12,240 | Fair |
| I029 over Ck | 1966 | 12,240 | Fair |
| I029 over Ck | 1970 | 9,960 | Fair |
| I029 over Ck | 1970 | 9,960 | Fair |
| I029 over Br Six Mile Ck | 1970 | 9,960 | Fair |
| US014 B over West Br Six Mile Ck | 1967 | 9,030 | Fair |
All bridges nearby: Brookings County, SD bridge conditions · every bridge in Brookings County · South Dakota bridges.
Background: how bridge ratings work · what "poor" and "structurally deficient" actually mean · how often bridges are inspected.