US Bridges

M-33|M-72|N Mount over Au Sable River

Fair

Oscoda County, Michigan · 0.7 MI N of S JCT M-72 · Structure no. 000000000008658

Built
1984
41 years old
Condition
Fair
inspected May 2023
Type
Stringer/Multi-beam or Girder
Steel
Length
160 ft
1 main span
Daily traffic
8,950
2021 count
Owner
State
State Highway Agency

About this bridge

M-33|M-72|N Mount over Au Sable River is a steel stringer/multi-beam or girder carrying M-33|M-72|N Mount over Au Sable River in Oscoda County, Michigan. It was built in 1984, so it is 41 years old, younger 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 8,950 vehicles a day, roughly 3% of them trucks, projected to reach 9,875 by 2041. The structure is 160 ft (48.8 m) long and 52 ft wide. If it were closed, the detour would be 11.2 mi (18 km).

Location

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CarriesM-33|M-72|N Mount
CrossesAu Sable River
Location0.7 MI N of S JCT M-72
RouteState Highway 33
CountyOscoda County
StateMichigan
Coordinates44.65993, -84.12896
Functional classRural Principal Arterial - Other

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.
Superstructure5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Substructure7 GoodSome minor problems.
Channel and channel protection8 Very GoodNo problems noted.
Last inspectionMay 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 alignment7: Better than present minimum criteria
Operating rating81.5 US tons
Inventory rating48.9 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialSteel
DeckConcrete, cast-in-place
Main spans1
Design loadHS 25 or greater
Structure length160 ft (48.8 m)
Longest span157 ft (48 m)
Deck width52 ft (15.8 m)
Roadway width48 ft (14.6 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic8,950 (2021)
Projected traffic9,875 by 2041
Trucks3%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed11.2 mi (18 km)
TollOn a free road
National Highway SystemYes

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-33|M-72|N Mount over Au Sable River built?

It was built in 1984, making it 41 years old in 2025.

What condition is M-33|M-72|N Mount over Au Sable 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 May 2023.

How much traffic does M-33|M-72|N Mount over Au Sable River carry?

About 8,950 vehicles per day (2021 count), of which roughly 3% are trucks.

How long is M-33|M-72|N Mount over Au Sable River?

The structure is 160 ft (48.8 m) long with a longest span of 157 ft (48 m) and a deck 52 ft wide.

Who owns M-33|M-72|N Mount over Au Sable River?

It is owned by the State Highway Agency.