US Bridges

I-75 NB over Mackinac Trail

Fair

Mackinac County, Michigan · 4.0 MI NE of M-123 · Structure no. 000000000005957

Built
1963
62 years old
Condition
Fair
inspected August 2024
Type
Stringer/Multi-beam or Girder
Steel
Length
120 ft
3 main spans
Daily traffic
2,039
2007 count
Owner
State
State Highway Agency

About this bridge

I-75 NB over Mackinac Trail is a steel stringer/multi-beam or girder carrying I-75 NB over Mackinac Trail in Mackinac County, Michigan. It was built in 1963, so it is 62 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 2,039 vehicles a day, roughly 9% of them trucks, projected to reach 5,205 by 2018. The structure is 120 ft (36.6 m) long and 44 ft wide. If it were closed, the detour would be 1.2 mi (2 km).

Location

Open in Google Maps
CarriesI-75 NB
CrossesMackinac Trail
Location4.0 MI NE of M-123
RouteInterstate 75
CountyMackinac County
StateMichigan
Coordinates46.01721, -84.71699
Functional classRural Principal Arterial - Interstate

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.
Substructure5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Last inspectionAugust 2024
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourBridge not over waterway
Structural evaluation5: Somewhat better than minimum adequacy to tolerate being left in place as is
Deck geometry6: Equal to present minimum criteria
Approach roadway alignment7: Better than present minimum criteria
Operating rating66 US tons
Inventory rating39.7 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialSteel
DeckConcrete, cast-in-place
Main spans3
Design loadHS 20 + Mod
Structure length120 ft (36.6 m)
Longest span46 ft (14.1 m)
Deck width44 ft (13.3 m)
Roadway width38 ft (11.7 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic2,039 (2007)
Projected traffic5,205 by 2018
Trucks9%
Lanes on structure2
Traffic directionOne-way traffic
CarriesHighway
CrossesHighway
Detour if closed1.2 mi (2 km)
TollOn a free road
National Highway SystemYes
Strategic Highway NetworkInterstate STRAHNET route

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—
NavigationNot applicable (no waterway)

Frequently asked questions

When was I-75 NB over Mackinac Trail built?

It was built in 1963, making it 62 years old in 2025.

What condition is I-75 NB over Mackinac Trail 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 August 2024.

How much traffic does I-75 NB over Mackinac Trail carry?

About 2,039 vehicles per day (2007 count), of which roughly 9% are trucks.

How long is I-75 NB over Mackinac Trail?

The structure is 120 ft (36.6 m) long with a longest span of 46 ft (14.1 m) and a deck 44 ft wide.

Who owns I-75 NB over Mackinac Trail?

It is owned by the State Highway Agency.