M-66 over Thornapple River
Barry County, Michigan · rated Fair in the 2025 National Bridge Inventory
United States Bridge Conditions2025 National Bridge Inventory, FHWACompiled
- M-66 over Thornapple River in Barry County, Michigan, is rated in fair condition in the 2025 National Bridge Inventory (as of ).
- Its lowest-rated component is the substructure, rated 6 (satisfactory condition) on the 0-9 scale.
- It was built in 1999, making it 26 years old at the 2025 inventory.
- It carries about 6,177 vehicles a day (traffic count year 2007).
- Its listed owner is the state highway agency.
- It is one of 35 of the 69 inventoried bridges in Barry County rated fair (50.7%); 15 (21.7%) 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 May 2024, on a 24-month routine inspection cycle.
- 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 → (42.6087, -85.09334)
Component ratings
| Component | Rating (2024) | Rating (2025) | FHWA scale meaning |
|---|---|---|---|
| Deck | 7 | 7 | Good condition |
| Superstructure | 7 | 7 | Good condition |
| Substructure | 6 | 6 | Satisfactory condition |
Bridge details
| Structure | Prestressed concrete stringer or multi-beam girder |
| Length | about 132 ft |
| Location | In Nashville |
| NBI structure number | 000000000000545 |
| Condition class | Fair |
| Traffic status (item 41) | Open, no restriction |
| Last inspection (item 90) | May 2024 |
| Inspection interval (item 91) | 24 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 Michigan department of transportation.
Busiest bridges in Barry County
| Bridge | Built | Vehicles/day | Condition |
|---|---|---|---|
| M-43 over Thornapple River | 1963 | 12,750 | Fair |
| M-37 over Duncan Creek | 1957 | 10,700 | Fair |
| Main Street over Thornapple River | 2015 | 8,000 | Good |
| Michigan Ave over Thornapple River | 2012 | 7,215 | Good |
| M-66 over Quaker Brook | 2019 | 6,083 | Good |
| M-66 over Quaker Brook | 1940 | 4,450 | Fair |
All bridges nearby: Barry County, MI bridge conditions · every bridge in Barry County · Michigan bridges.
Background: how bridge ratings work · what "poor" and "structurally deficient" actually mean · how often bridges are inspected.