US Bridges

M-21 over Shiawassee River

Fair

Shiawassee County, Michigan · In Owosso · Structure no. 000000000009773

Built
1970
55 years old
Condition
Fair
inspected July 2023
Type
Stringer/Multi-beam or Girder
Steel
Length
132 ft
2 main spans
Daily traffic
22,689
2007 count
Owner
State
State Highway Agency

About this bridge

M-21 over Shiawassee River is a steel stringer/multi-beam or girder carrying M-21 over Shiawassee River in Shiawassee County, Michigan. It was built in 1970, so it is 55 years old, older than the Michigan average of 48.3 years.

The most recent inspection reported to the Federal Highway Administration rates it in fair condition with a lowest component rating of 6 out of 9. The lowest-rated primary component is rated 5 or 6. Minor deterioration is present but the structure is sound.

It carries about 22,689 vehicles a day, roughly 2% of them trucks, projected to reach 26,205 by 2018. The structure is 132 ft (40.2 m) long and 88 ft wide. If it were closed, the detour would be 1.9 mi (3 km).

Location

Open in Google Maps
CarriesM-21
CrossesShiawassee River
LocationIn Owosso
RouteState Highway 21
CountyShiawassee County
StateMichigan
Coordinates42.99756, -84.17384
Functional classUrban Minor Arterial

Condition and inspection

Fair

The lowest-rated primary component is rated 5 or 6. Minor deterioration is present but the structure is sound.

ComponentRatingMeaning
Deck6 SatisfactoryStructural elements show some minor deterioration.
Superstructure6 SatisfactoryStructural elements show some minor deterioration.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Channel and channel protection6 SatisfactoryStructural elements show some minor deterioration.
Last inspectionJuly 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourScour critical; foundations unstable for calculated scour conditions
Structural evaluation6: Equal to present minimum criteria
Deck geometry7: Better than present minimum criteria
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating69.3 US tons
Inventory rating41.4 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialSteel
DeckConcrete, cast-in-place
Main spans2
Design loadHS 20
Structure length132 ft (40.2 m)
Longest span66 ft (20.1 m)
Deck width88 ft (26.8 m)
Roadway width64 ft (19.5 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic22,689 (2007)
Projected traffic26,205 by 2018
Trucks2%
Lanes on structure4
Traffic directionTwo-way traffic
CarriesHighway and pedestrian
CrossesWaterway
Detour if closed1.9 mi (3 km)
TollOn a free road
National Highway SystemNo

Ownership and planned work

OwnerState Highway Agency
Maintained byState Highway Agency
Historic statusNot eligible for the National Register of Historic Places
Work proposedNone recorded
Estimated improvement cost—
NavigationNo navigation control on waterway

Frequently asked questions

When was M-21 over Shiawassee River built?

It was built in 1970, making it 55 years old in 2025.

What condition is M-21 over Shiawassee River in?

The National Bridge Inventory rates it in fair condition. The lowest-rated primary component is rated 5 or 6. Minor deterioration is present but the structure is sound. The last reported inspection was in July 2023.

How much traffic does M-21 over Shiawassee River carry?

About 22,689 vehicles per day (2007 count), of which roughly 2% are trucks.

How long is M-21 over Shiawassee River?

The structure is 132 ft (40.2 m) long with a longest span of 66 ft (20.1 m) and a deck 88 ft wide.

Who owns M-21 over Shiawassee River?

It is owned by the State Highway Agency.