US Bridges

M-20 over Chippewa River

Fair

Isabella County, Michigan · 7.2 MI E of Mecosta Col · Structure no. 000000000004263

Built
1934
91 years old, rebuilt 1973
Condition
Fair
inspected March 2023
Type
Stringer/Multi-beam or Girder
Steel
Length
80 ft
2 main spans
Daily traffic
6,611
2007 count
Owner
State
State Highway Agency

About this bridge

M-20 over Chippewa River is a steel stringer/multi-beam or girder carrying M-20 over Chippewa River in Isabella County, Michigan. It was built in 1934 and reconstructed in 1973, so it is 91 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 6,611 vehicles a day, roughly 6% of them trucks, projected to reach 6,683 by 2018. The structure is 80 ft (24.3 m) long and 50 ft wide. If it were closed, the detour would be 3.1 mi (5 km).

Location

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CarriesM-20
CrossesChippewa River
Location7.2 MI E of Mecosta Col
RouteState Highway 20
CountyIsabella County
StateMichigan
Coordinates43.59701, -84.94317
Functional classRural 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.
Superstructure7 GoodSome minor problems.
Substructure7 GoodSome minor problems.
Channel and channel protection7 GoodSome minor problems.
Last inspectionMarch 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourScour critical; foundations unstable for calculated scour conditions
Structural evaluation7: Better than present minimum criteria
Deck geometry9: Superior to present desirable criteria
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment7: Better than present minimum criteria
Operating rating107.1 US tons
Inventory rating69.3 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialSteel
DeckConcrete, cast-in-place
Main spans2
Design loadHS 20
Structure length80 ft (24.3 m)
Longest span40 ft (12.2 m)
Deck width50 ft (15.2 m)
Roadway width48 ft (14.6 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic6,611 (2007)
Projected traffic6,683 by 2018
Trucks6%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed3.1 mi (5 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 proposedDeck replacement with only incidental widening
Estimated improvement cost—
NavigationNo navigation control on waterway

Frequently asked questions

When was M-20 over Chippewa River built?

It was built in 1934, making it 91 years old in 2025. It was reconstructed in 1973.

What condition is M-20 over Chippewa 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 March 2023.

How much traffic does M-20 over Chippewa River carry?

About 6,611 vehicles per day (2007 count), of which roughly 6% are trucks.

How long is M-20 over Chippewa River?

The structure is 80 ft (24.3 m) long with a longest span of 40 ft (12.2 m) and a deck 50 ft wide.

Who owns M-20 over Chippewa River?

It is owned by the State Highway Agency.