US Bridges

M-20 over N Br Chippewa River

Fair

Isabella County, Michigan · 4.5 MI W of US-27BR · Structure no. 000000000004264

Built
1934
91 years old, rebuilt 1964
Condition
Fair
inspected March 2023
Type
Stringer/Multi-beam or Girder
Steel
Length
50 ft
1 main span
Daily traffic
8,359
2007 count
Owner
State
State Highway Agency

About this bridge

M-20 over N Br Chippewa River is a steel stringer/multi-beam or girder carrying M-20 over N Br Chippewa River in Isabella County, Michigan. It was built in 1934 and reconstructed in 1964, 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 5 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 8,359 vehicles a day, roughly 4% of them trucks, projected to reach 9,678 by 2018. The structure is 50 ft (15.2 m) long and 43 ft wide. If it were closed, the detour would be 3.1 mi (5 km).

Location

Open in Google Maps
CarriesM-20
CrossesN Br Chippewa River
Location4.5 MI W of US-27BR
RouteState Highway 20
CountyIsabella County
StateMichigan
Coordinates43.59704, -84.85496
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
Deck5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Superstructure7 GoodSome minor problems.
Substructure5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Channel and channel protection4 PoorAdvanced section loss, deterioration, spalling or scour.
Last inspectionMarch 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourScour critical; foundations unstable for calculated scour conditions
Structural evaluation5: Somewhat better than minimum adequacy to tolerate being left in place as is
Deck geometry5: Somewhat better than minimum adequacy to tolerate being left in place as is
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment7: Better than present minimum criteria
Operating rating80.7 US tons
Inventory rating48.2 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialSteel
DeckConcrete, cast-in-place
Main spans1
Design loadHS 20
Structure length50 ft (15.2 m)
Longest span50 ft (15.2 m)
Deck width43 ft (13.2 m)
Roadway width41 ft (12.5 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic8,359 (2007)
Projected traffic9,678 by 2018
Trucks4%
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 proposedNone recorded
Estimated improvement cost—
NavigationNo navigation control on waterway

Frequently asked questions

When was M-20 over N Br Chippewa River built?

It was built in 1934, making it 91 years old in 2025. It was reconstructed in 1964.

What condition is M-20 over N Br 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 N Br Chippewa River carry?

About 8,359 vehicles per day (2007 count), of which roughly 4% are trucks.

How long is M-20 over N Br Chippewa River?

The structure is 50 ft (15.2 m) long with a longest span of 50 ft (15.2 m) and a deck 43 ft wide.

Who owns M-20 over N Br Chippewa River?

It is owned by the State Highway Agency.