M-21 over Flat River
GoodKent County, Michigan · In Lowell (107 E Main St) · Structure no. 000000000004856
- Built
- 1940
- 85 years old, rebuilt 2010
- Condition
- Good
- inspected October 2024
- Type
- Box Beam or Girders - Single or Spread
- Prestressed Concrete
- Length
- 49 ft
- 1 main span
- Daily traffic
- 18,836
- 2007 count
- Owner
- State
- State Highway Agency
About this bridge
M-21 over Flat River is a prestressed concrete box beam or girders - single or spread carrying M-21 over Flat River in Kent County, Michigan. It was built in 1940 and reconstructed in 2010, so it is 85 years old, older than the Michigan average of 48.3 years.
The most recent inspection reported to the Federal Highway Administration rates it in good condition with a lowest component rating of 7 out of 9. All primary components (deck, superstructure, substructure, or culvert) are rated 7 or higher. No significant problems were noted.
It carries about 18,836 vehicles a day, roughly 4% of them trucks, projected to reach 14,750 by 2030. The structure is 49 ft (14.9 m) long and 74 ft wide. If it were closed, the detour would be 1.9 mi (3 km).
Location
Open in Google MapsCondition and inspection
All primary components (deck, superstructure, substructure, or culvert) are rated 7 or higher. No significant problems were noted.
| Component | Rating | Meaning |
|---|---|---|
| Deck | 7 Good | Some minor problems. |
| Superstructure | 8 Very Good | No problems noted. |
| Substructure | 7 Good | Some minor problems. |
| Channel and channel protection | 8 Very Good | No problems noted. |
Structure
Traffic and service
Ownership and planned work
Frequently asked questions
When was M-21 over Flat River built?
It was built in 1940, making it 85 years old in 2025. It was reconstructed in 2010.
What condition is M-21 over Flat River in?
The National Bridge Inventory rates it in good condition. All primary components (deck, superstructure, substructure, or culvert) are rated 7 or higher. No significant problems were noted. The last reported inspection was in October 2024.
How much traffic does M-21 over Flat River carry?
About 18,836 vehicles per day (2007 count), of which roughly 4% are trucks.
How long is M-21 over Flat River?
The structure is 49 ft (14.9 m) long with a longest span of 46 ft (14.1 m) and a deck 74 ft wide.
Who owns M-21 over Flat River?
It is owned by the State Highway Agency.