I-75 over Straits of Mackinac
Emmet County, Michigan · rated Fair in the 2025 National Bridge Inventory
United States Bridge Conditions2025 National Bridge Inventory, FHWACompiled
- I-75 over Straits of Mackinac in Emmet County, Michigan, is rated in fair condition in the 2025 National Bridge Inventory (as of ).
- Its lowest-rated component is the deck, rated 6 (satisfactory condition) on the 0-9 scale.
- It was built in 1957, making it 68 years old at the 2025 inventory.
- It carries about 11,926 vehicles a day (traffic count year 2021).
- It is one of 16 of the 38 inventoried bridges in Emmet County rated fair (42.1%); 1 (2.6%) are rated poor.
- Its traffic status in the 2025 inventory is posted for load (NBI item 41).
- It was rated good in the 2024 inventory and is now fair (deck 7 to 6, superstructure 7 to 6, substructure 8 to 7).
- Its most recent inspection on record is dated July 2024, on a 12-month routine inspection cycle.
- It has fracture-critical members (NBI item 92A): steel tension members without a redundant load path, which get their own scheduled inspections.
- 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 → (45.83684, -84.72481)
Component ratings
| Component | Rating (2024) | Rating (2025) | FHWA scale meaning |
|---|---|---|---|
| Deck | 7 | 6 | Satisfactory condition |
| Superstructure | 7 | 6 | Satisfactory condition |
| Substructure | 8 | 7 | Good condition |
Bridge details
| Structure | Steel suspension |
| Length | about 19,247 ft |
| Location | Mackinaw City-st Ignace |
| NBI structure number | 000000000002456 |
| Condition class | Fair |
| Traffic status (item 41) | Posted for load |
| Last inspection (item 90) | July 2024 |
| Inspection interval (item 91) | 12 months |
| Scour (item 113) | 8: foundations stable, scour above the top of the footing |
| Fracture critical (item 92A) | Yes |
Source: FHWA National Bridge Inventory, 2025 data as reported by the Michigan department of transportation.
Busiest bridges in Emmet County
| Bridge | Built | Vehicles/day | Condition |
|---|---|---|---|
| US-31|W Mitchellst over Bear River | 1930 | 28,667 | Fair |
| I-75 S Appr over Huron Ave | 1957 | 11,076 | Fair |
| I-75 N Appr over Straits of Mackinac | 1942 | 11,076 | Fair |
| I-75 NB over D&m RR (abn) | 1957 | 10,100 | Fair |
| I-75 NB over Central St | 1957 | 10,100 | Fair |
| M-68 over Crooked River | 1937 | 8,053 | Fair |
All bridges nearby: Emmet County, MI bridge conditions · every bridge in Emmet County · Michigan bridges.
Background: how bridge ratings work · what "poor" and "structurally deficient" actually mean · how often bridges are inspected.