M-100 over Thornapple Drain
Eaton County, Michigan · rated Good in the 2025 National Bridge Inventory
United States Bridge Conditions2025 National Bridge Inventory, FHWACompiled
- M-100 over Thornapple Drain in Eaton County, Michigan, is rated in good condition in the 2025 National Bridge Inventory (as of ).
- Its lowest-rated component is the culvert, rated 9 (excellent condition) on the 0-9 scale.
- It was built in 2015, making it 10 years old at the 2025 inventory.
- It carries about 5,425 vehicles a day (traffic count year 2015).
- Its listed owner is the state highway agency.
- It is one of 63 of the 202 inventoried bridges in Eaton County rated good (31.2%); 11 (5.4%) 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 July 2023, on a 24-month routine inspection cycle.
- 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.
View this bridge on a map → (42.67323, -84.73942)
Component ratings
| Component | Rating (2024) | Rating (2025) | FHWA scale meaning |
|---|---|---|---|
| Culvert | 9 | 9 | Excellent condition |
Bridge details
| Structure | Concrete culvert |
| Length | about 34 ft |
| Location | 3.5 Mi N of I-69 |
| NBI structure number | 000000000002283 |
| Condition class | Good |
| Traffic status (item 41) | Open, no restriction |
| Last inspection (item 90) | July 2023 |
| Inspection interval (item 91) | 24 months |
| Scour (item 113) | 8: foundations stable, scour above the top of the footing |
Source: FHWA National Bridge Inventory, 2025 data as reported by the Michigan department of transportation.
Busiest bridges in Eaton County
| Bridge | Built | Vehicles/day | Condition |
|---|---|---|---|
| I-96 WB over Grand Riv & Billwood Hwy | 2023 | 47,900 | Good |
| I-96 EB over M-43 | 1962 | 31,250 | Fair |
| I-96 WB over M-43 | 1962 | 31,250 | Fair |
| Otto Road over I-69 | 1989 | 27,800 | Fair |
| I-96 EB over Grand River | 1962 | 27,100 | Fair |
| I-96 WB over Grand River | 1962 | 27,100 | Fair |
All bridges nearby: Eaton County, MI bridge conditions · every bridge in Eaton County · Michigan bridges.
Background: how bridge ratings work · what "poor" and "structurally deficient" actually mean · how often bridges are inspected.