US Bridges

I-75 N Appr over Straits of Mackinac

FairPosted for load

Emmet County, Michigan · N of Mackinac Br (causway · Structure no. 000000000002457

Built
1942
83 years old, rebuilt 1985
Condition
Fair
inspected July 2024
Type
Stringer/Multi-beam or Girder
Steel
Length
90 ft
3 main spans
Daily traffic
11,076
2007 count
Owner
Toll Authority
State Toll Authority

About this bridge

I-75 N Appr over Straits of Mackinac is a steel stringer/multi-beam or girder carrying I-75 N Appr over Straits of Mackinac in Emmet County, Michigan. It was built in 1942 and reconstructed in 1985, so it is 83 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. Its operating status is: posted for load restriction.

It carries about 11,076 vehicles a day, roughly 7% of them trucks, projected to reach 16,229 by 2015. The structure is 90 ft (27.4 m) long and 59 ft wide. If it were closed, the detour would be 124.3 mi (200 km).

Location

Open in Google Maps
CarriesI-75 N Appr
CrossesStraits of Mackinac
LocationN of Mackinac Br (causway
RouteInterstate 75
CountyEmmet County
StateMichigan
Coordinates45.84573, -84.72347
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
Deck7 GoodSome minor problems.
Superstructure7 GoodSome minor problems.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Channel and channel protection8 Very GoodNo problems noted.
Last inspectionJuly 2024
Inspection intervalevery 12 months
Operating statusPosted for load restriction
ScourFoundations stable; scour above top of footing
Structural evaluation6: Equal to present minimum criteria
Deck geometry3: Basically intolerable, requiring high priority of corrective action
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating60.7 US tons
Inventory rating46.7 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialSteel
DeckConcrete, cast-in-place
Main spans3
Design loadHS 20
Structure length90 ft (27.4 m)
Longest span30 ft (9.1 m)
Deck width59 ft (18.1 m)
Roadway width56 ft (17.1 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic11,076 (2007)
Projected traffic16,229 by 2015
Trucks7%
Lanes on structure4
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed124.3 mi (200 km)
TollToll bridge
National Highway SystemYes
Strategic Highway NetworkInterstate STRAHNET route

Ownership and planned work

OwnerState Toll Authority
Maintained byState Toll Authority
Historic statusListed on the National Register of Historic Places
Work proposedNone recorded
Estimated improvement cost—
NavigationNavigation control on waterway (bridge permit required)

Frequently asked questions

When was I-75 N Appr over Straits of Mackinac built?

It was built in 1942, making it 83 years old in 2025. It was reconstructed in 1985.

What condition is I-75 N Appr over Straits of Mackinac 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 July 2024.

How much traffic does I-75 N Appr over Straits of Mackinac carry?

About 11,076 vehicles per day (2007 count), of which roughly 7% are trucks.

How long is I-75 N Appr over Straits of Mackinac?

The structure is 90 ft (27.4 m) long with a longest span of 30 ft (9.1 m) and a deck 59 ft wide.

Who owns I-75 N Appr over Straits of Mackinac?

It is owned by the State Toll Authority.