US-23 over Thunder Bay River
Alpena County, Michigan · rated Fair in the 2025 National Bridge Inventory
United States Bridge Conditions2025 National Bridge Inventory, FHWACompiled
- US-23 over Thunder Bay River in Alpena 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 1932 and reconstructed in 1998, making it 93 years old at the 2025 inventory.
- It carries about 16,200 vehicles a day (traffic count year 2007).
- Its listed owner is the state highway agency.
- It is one of 19 of the 32 inventoried bridges in Alpena County rated fair (59.4%); 2 (6.2%) 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 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 → (45.07461, -83.4481)
Component ratings
| Component | Rating (2024) | Rating (2025) | FHWA scale meaning |
|---|---|---|---|
| Deck | 6 | 6 | Satisfactory condition |
| Superstructure | 7 | 7 | Good condition |
| Substructure | 7 | 7 | Good condition |
Bridge details
| Structure | Prestressed concrete multiple box beam |
| Length | about 183 ft |
| Location | In Alpena |
| NBI structure number | 000000000000335 |
| Condition class | Fair |
| Traffic status (item 41) | Open, no restriction |
| Last inspection (item 90) | May 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 Michigan department of transportation.
Busiest bridges in Alpena County
| Bridge | Built | Vehicles/day | Condition |
|---|---|---|---|
| Second Avenue over Thunder Bay River | 1939 | 15,700 | Fair |
| Bagley Street over Thunder Bay River | 2021 | 15,000 | Good |
| US-23 over S Br Devil River | 1936 | 5,537 | Fair |
| US-23 over N Br Devil River | 1933 | 5,537 | Fair |
| M-32 over Bean Creek | 1934 | 5,505 | Fair |
| M-32 over S Br Thunder Bay River | 1931 | 5,505 | Fair |
All bridges nearby: Alpena County, MI bridge conditions · every bridge in Alpena County · Michigan bridges.
Background: how bridge ratings work · what "poor" and "structurally deficient" actually mean · how often bridges are inspected.