US Bridges

M-66 over Prairie River

Fair

St. Joseph County, Michigan · 0.4 MI S of Findley Road · Structure no. 000000000010276

Built
1931
94 years old, rebuilt 1980
Condition
Fair
inspected September 2023
Type
Stringer/Multi-beam or Girder
Steel
Length
60 ft
1 main span
Daily traffic
5,400
2018 count
Owner
State
State Highway Agency

About this bridge

M-66 over Prairie River is a steel stringer/multi-beam or girder carrying M-66 over Prairie River in St. Joseph County, Michigan. It was built in 1931 and reconstructed in 1980, so it is 94 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 5,400 vehicles a day, roughly 6% of them trucks, projected to reach 6,000 by 2038. The structure is 60 ft (18.3 m) long and 49 ft wide. If it were closed, the detour would be 3.7 mi (6 km).

Location

Open in Google Maps
CarriesM-66
CrossesPrairie River
Location0.4 MI S of Findley Road
RouteState Highway 66
CountySt. Joseph County
StateMichigan
Coordinates41.88864, -85.40967
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
Deck7 GoodSome minor problems.
Superstructure5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Channel and channel protection6 SatisfactoryStructural elements show some minor deterioration.
Last inspectionSeptember 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 geometry9: Superior to present desirable criteria
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating71.8 US tons
Inventory rating42.9 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialSteel
DeckConcrete, cast-in-place
Main spans1
Design loadHS 20
Structure length60 ft (18.3 m)
Longest span60 ft (18.3 m)
Deck width49 ft (14.9 m)
Roadway width45 ft (13.7 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic5,400 (2018)
Projected traffic6,000 by 2038
Trucks6%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed3.7 mi (6 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-66 over Prairie River built?

It was built in 1931, making it 94 years old in 2025. It was reconstructed in 1980.

What condition is M-66 over Prairie 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 September 2023.

How much traffic does M-66 over Prairie River carry?

About 5,400 vehicles per day (2018 count), of which roughly 6% are trucks.

How long is M-66 over Prairie River?

The structure is 60 ft (18.3 m) long with a longest span of 60 ft (18.3 m) and a deck 49 ft wide.

Who owns M-66 over Prairie River?

It is owned by the State Highway Agency.