US Bridges

M-46 over Black River

Poor

Sanilac County, Michigan · 5.6 MI E of M-19 · Structure no. 000000000009478

Built
1947
78 years old
Condition
Poor
inspected May 2024
Type
Stringer/Multi-beam or Girder
Steel
Length
75 ft
1 main span
Daily traffic
5,462
2007 count
Owner
State
State Highway Agency

About this bridge

M-46 over Black River is a steel stringer/multi-beam or girder carrying M-46 over Black River in Sanilac County, Michigan. It was built in 1947, so it is 78 years old, older than the Michigan average of 48.3 years.

The most recent inspection reported to the Federal Highway Administration rates it in poor condition with a lowest component rating of 4 out of 9. The lowest-rated primary component is rated 4 or below, indicating advanced deterioration. Poor does not mean unsafe; such bridges are inspected more often and may carry load restrictions.

It carries about 5,462 vehicles a day, roughly 3% of them trucks, projected to reach 9,011 by 2018. The structure is 75 ft (22.8 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-46
CrossesBlack River
Location5.6 MI E of M-19
RouteState Highway 46
CountySanilac County
StateMichigan
Coordinates43.42499, -82.72181
Functional classRural Principal Arterial - Other

Condition and inspection

Poor

The lowest-rated primary component is rated 4 or below, indicating advanced deterioration. Poor does not mean unsafe; such bridges are inspected more often and may carry load restrictions.

ComponentRatingMeaning
Deck4 PoorAdvanced section loss, deterioration, spalling or scour.
Superstructure4 PoorAdvanced section loss, deterioration, spalling or scour.
Substructure4 PoorAdvanced section loss, deterioration, spalling or scour.
Channel and channel protection4 PoorAdvanced section loss, deterioration, spalling or scour.
Last inspectionMay 2024
Inspection intervalevery 12 months
Operating statusOpen, no restriction
ScourScour critical; foundations unstable for calculated scour conditions
Structural evaluation4: Meets minimum tolerable limits to be left in place as is
Deck geometry4: Meets minimum tolerable limits to be left in place as is
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating63.6 US tons
Inventory rating38.3 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialSteel
DeckConcrete, cast-in-place
Main spans1
Design loadHS 20
Structure length75 ft (22.8 m)
Longest span75 ft (22.8 m)
Deck width43 ft (13.2 m)
Roadway width38 ft (11.5 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic5,462 (2007)
Projected traffic9,011 by 2018
Trucks3%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed3.1 mi (5 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 proposedDeck replacement with only incidental widening
Estimated improvement cost$38,000
NavigationNo navigation control on waterway

Frequently asked questions

When was M-46 over Black River built?

It was built in 1947, making it 78 years old in 2025.

What condition is M-46 over Black River in?

The National Bridge Inventory rates it in poor condition. The lowest-rated primary component is rated 4 or below, indicating advanced deterioration. Poor does not mean unsafe; such bridges are inspected more often and may carry load restrictions. The last reported inspection was in May 2024.

How much traffic does M-46 over Black River carry?

About 5,462 vehicles per day (2007 count), of which roughly 3% are trucks.

How long is M-46 over Black River?

The structure is 75 ft (22.8 m) long with a longest span of 75 ft (22.8 m) and a deck 43 ft wide.

Who owns M-46 over Black River?

It is owned by the State Highway Agency.