Michigan Bridge Conditions: Salt, Steel, and a Ticking Clock

The Headline Numbers

Michigan has 11,397 bridges, and 1,250 of them are rated in poor condition. That is an 11% poor rate, which puts the state 9th nationally and nearly double the 6.7% national average. (ARTBA 2025)

Three states share the 11% tier: Louisiana, North Dakota, and Michigan. But their inventories are very different in size. Louisiana has 12,684 bridges with 1,423 in poor condition, and North Dakota has 4,250 with 470 poor. Michigan sits between them with the second-largest count and the second-highest raw number of poor bridges in the group. (ARTBA 2025)

The three states also share a rate but not a story. Louisiana's 11% is driven by water, hurricanes, and coastal subsidence. North Dakota's is the aftermath of the Bakken oil boom breaking county bridges faster than oil revenue could repair them. Michigan's version centers on industrial-scale road salt and a funding structure that is about to lose its largest backstop. (ARTBA 2025)

The full state profile is available on ARTBA's Michigan bridge report.

The False Equilibrium

Michigan's 11% headline has held steady since at least 2018, which on the surface looks like stability. It is not. The underlying composition of the state's bridge inventory has been shifting in the wrong direction throughout that period, and the percentage has remained flat only because repair programs are removing bridges from the poor category at roughly the same pace that new bridges are falling into it.

Between 2018 and 2022, the share of Michigan bridges rated in good condition dropped from 40% to 35%, while bridges rated fair rose from 50% to 54%. (MDOT) The pipeline of bridges sliding from fair toward poor is growing. MDOT projections show fair-condition bridges reaching 56% by 2027 under current funding levels, and a TRIP/Michigan Public projection puts the poor rate at 15% by 2036 without additional investment. (MDOT; TRIP)

The state has done real work during this period. More than 1,900 bridges have been repaired or replaced since 2019. (MDOT) That volume kept the 11% number from climbing, but it did not prevent the broader inventory from deteriorating underneath the headline figure. The balance between repair output and incoming deterioration is what created the appearance of stability, and that balance depends on a funding source that is about to disappear.

The Funding Cliff

The Rebuilding Michigan bonding program, a $3.5 billion initiative launched in 2020, has been the primary backstop keeping the 11% number stable. Approximately $700 million in authorized bond funding remains. When the program ends, MDOT's annual reconstruction budget drops from $495 million to $222 million, a cut of more than half. (MDOT)

The 2025 fuel tax reform restructured the state excise tax to 52.4 cents per gallon and dedicated all revenue to transportation, but the net increase to motorists was only about 1.5 cents per gallon. That does not close the gap. (Michigan Legislature)

Federal IIJA money helps. Michigan received a $563 million Bridge Formula Program allocation, and the state is eligible for additional competitive grants. But IIJA funding is time-limited. It extends the runway without changing the underlying math. (FHWA)

MDOT has released region-by-region lists identifying more than 100 trunkline bridges at risk of closure by 2035, a deliberate public accounting of what reduced funding would mean in practice. (MDOT)

Road Salt and the Great Lakes Corrosion Cycle

Michigan applies roughly 2 million tons of road salt every year, about 400 pounds per resident. The EPA estimates that every $50 ton of road salt causes approximately $750 in damage to concrete, bridges, and vehicles. Applied to Michigan's volume, that translates to roughly $1.5 billion in salt-related infrastructure damage per year. (EPA-derived estimate)

Chloride corrosion is the primary mechanism, but it does not work alone. Michigan's freeze-thaw cycling compounds the damage: repeated midwinter thaws crack and spall concrete deck surfaces and substructures, and the salt penetrates deeper with each cycle. Lake-effect snow on both peninsulas drives the salt volume higher than most other cold-climate states, which means both the chemical exposure and the mechanical stress are more severe than national averages. (MDOT)

Two-thirds of MDOT's bridges have exceeded their original design lives, and an MDOT study found that prestressed concrete box beam service life in Michigan is less than 50 years. (MDOT) Roads that would otherwise last 20 years need repair in 10. The combination of aggressive deicing, Great Lakes weather, and an aging inventory means Michigan's bridges deteriorate faster than the national norm, which is why holding at 11% requires spending at a rate the state cannot sustain after the bonding program ends.

The Ownership Gap

MDOT owns about 4,500 of Michigan's 11,000+ bridges, roughly 40% of the inventory. The remaining 60% belong to counties, cities, villages, and townships. The condition gap between state-owned and locally owned bridges is substantial: 6% of state-owned bridges are rated poor, compared with 13% of city- and county-owned bridges. (ASCE 2023 Michigan Infrastructure Report)

County / Category	Bridges	% Poor	Key Context
Benzie	—	28%	Highest county poor rate
Arenac	—	23.8%
Crawford	—	23.6%
Metro Region	—	—	180 anticipated poor; 37 at risk of closure by 2035
Statewide	11,397	11%	#9 nationally

MDOT's bridge bundling program, which completed 28 local bridge replacements and removals in four years, exists specifically to close the gap between state and local conditions. The FY2026 budget includes a $100 million per year Neighborhood Roads Fund for local critical bridge repairs, running through FY2030. (MDOT)

But local agencies own the majority of the worst bridges and operate with the thinnest budgets. The bundling program and the Neighborhood Roads Fund are real commitments, but they are working against an inventory where the local poor rate is more than double the state rate.

What Poor Bridges Cost Michigan

Approximately $860 billion in freight moves through Michigan annually, and 38% of the half-trillion-dollar annual U.S.-Canada trade crosses the state. (TRIP) The auto industry's just-in-time supply chains depend on reliable bridge access between plants, suppliers, and assembly facilities. A posted bridge on a truck route does not just create a detour; it can disrupt the timing of an entire production line.

TRIP estimates that poor roads and bridges cost Michigan drivers $17.3 billion annually in vehicle repair costs, congestion delays, and safety impacts (TRIP), according to the TRIP Michigan report. More than 1,000 bridges now carry posted weight limits, forcing heavier vehicles onto longer routes. (MDOT)

If the 100+ bridge closures MDOT projects by 2035 materialize, roughly 1.8 million daily road users will be affected. That projection is not a worst case. It is the department's own assessment of what happens at current funding levels. (MDOT)

The Zilwaukee Bridge

The 1.4-mile prestressed concrete bridge on I-75 over the Saginaw River is Michigan's most prominent bridge story, and it connects every theme on this page: salt damage, aging infrastructure, and the cost of keeping a critical span functional without replacing it.

Construction in the 1980s was plagued by an engineering error that caused a dramatic sag in one of the spans, delaying completion by years. In 2008, a bearing replacement project went wrong when crews drilled into reinforcing steel and installed improperly designed bearings. MDOT added external steel reinforcement to compensate. (MDOT)

Conventional road salt has been banned on the Zilwaukee Bridge entirely. MDOT uses calcium magnesium acetate instead, a deicing agent that costs 50 times as much. The bridge required $2.9 million in preventive maintenance in 2025 alone, with span closures lasting months at a time. In December 2025, freezing rain caused 11 or more crashes and forced a full closure of the bridge. (MDOT)

The Zilwaukee Bridge carries heavy I-75 traffic between Detroit and northern Michigan. It is one bridge, but it illustrates the broader math: when salt has already shortened a structure's life and the original construction had problems of its own, the cost of maintenance escalates well beyond normal budgets. Michigan has thousands of bridges aging under similar chemical and thermal stress, most of them without the political visibility that keeps Zilwaukee funded.