Frost Law in Michigan: Weight Limits, Exemptions, and Fines

Michigan’s frost laws temporarily cut how much weight trucks can carry on public roads during the spring thaw. Axle loads drop 25% on concrete roads and roads with a concrete base, and 35% on asphalt, gravel, dirt, and other surfaces, under MCL 257.722.¹ The restrictions exist because the ground thaws from the top down, trapping water between the softening road surface and the still-frozen subsoil. That saturated layer cannot support summer loads, and heavy traffic over it cracks and deforms pavement that costs far more to rebuild than to protect.

When the Restrictions Are in Effect

The statute names March, April, and May as the seasonal restriction months, but the Michigan Department of Transportation can start restrictions earlier or lift them sooner depending on actual conditions.¹ MDOT sets the dates each year by measuring frost depths along state highways, watching road conditions, and tracking weather forecasts. Restrictions remain in place until the frost line drops far enough for trapped moisture to drain and the roadbed to firm up again.²

Restrictions roll out from south to north as spring progresses. In 2026, MDOT imposed restrictions across southern Michigan starting February 17 and began lifting them in the southernmost areas by March 9, while northern Michigan stayed restricted for weeks longer.³ Because dates shift year to year, check the MDOT Spring Weight Restriction Bulletins and the MDOT Truck Operator’s Map before routing any heavy load in late winter or spring. County road agencies post the same information for their roads.

How Much Weight You Can Carry

The reduction depends on what the road is made of. Concrete roads and roads with a concrete base get a 25% cut from the normal axle maximums. Everything else (asphalt, gravel, dirt) gets a steeper 35% cut because those surfaces deform more easily when the subgrade is saturated.¹

Normal maximum single-axle load under MCL 257.722 is 18,000 pounds when axles are spaced nine feet or more apart. During restrictions, that becomes 13,500 pounds on concrete and 11,700 pounds on other surfaces. Axles spaced between 3.5 and 9 feet apart, normally capped at 13,000 pounds, drop proportionally. On designated heavier-loading highways, tandem axles that normally carry up to 16,000 pounds each fall to 10,400 pounds on non-concrete roads.¹

Wheel load by tire width also drops. The normal cap of 700 pounds per inch of tire width falls to 525 pounds per inch on concrete and 450 pounds per inch on other surfaces.¹ Enforcement is based on per-axle measurements, not just gross vehicle weight, so verify both before you move.

Speed Limits During the Thaw

Frost-law season brings reduced speeds on some roads along with the weight cuts. County road commissions commonly cap vehicles over 10,000 pounds at 35 miles per hour on roads under their jurisdiction during the restricted period. The statute itself requires a 35 mph cap for certain exempt vehicles, including public utility trucks heading to emergency work and propane delivery vehicles operating under the residential exception.¹ Confirm specific limits with the county road commission or watch for posted signs on the route.

Who Is Exempt

Several categories of vehicles can run at or near normal weights during restrictions, but most exemptions come with conditions that must be followed to the letter.

Agricultural Haulers

Vehicles picking up or delivering agricultural commodities to or from a farm are exempt from the seasonal reductions, but only if the operator notifies the relevant county road commission at least 48 hours before the pickup or delivery. The commission then issues a permit specifying the approved route, the time window, and a maximum speed if the commission requires one. The fee is limited to the commission’s actual administrative cost.¹ Skip the 48-hour notice and the exemption is gone, even if the cargo qualifies.

Public Utility Vehicles

Public utility vehicles responding to emergencies on restricted roads are exempt, but they must travel at no more than 35 miles per hour. For non-emergency work, the utility or its subcontractor applies to the county road commission for a seasonal truck permit. The commission may charge a fee and may require proof of insurance.¹

Propane Delivery and School Buses

Propane delivery vehicles serving residential customers are exempt if the tank is filled to no more than 50% of capacity and the vehicle stays at or below 35 miles per hour. School buses are also exempt from the seasonal reductions.¹

Permits If You Don’t Qualify for an Exemption

Operators who need to move heavy loads during restrictions but don’t fit a statutory exemption can apply for a variance permit through the relevant county road commission. These permits specify the approved route, travel dates, and any conditions such as speed limits or time-of-day windows. Fees vary by county; some commissions charge $25 or more and may require a bond to cover potential road damage.⁴ Permits are not automatic. The commission weighs the urgency of the move against the likely road damage, so apply well in advance.

What a Violation Costs

Overweight fines during frost-law season are punishing because the reduced limits make it easy to trigger a large overage. MCL 257.724 sets a graduated civil fine based on how far over the limit the vehicle is:⁵

Up to 2,000 lbs over: 3 cents per pound of excess over 1,000
2,001–3,000 lbs over: 6 cents per pound of excess
3,001–4,000 lbs over: 9 cents per pound of excess
4,001–5,000 lbs over: 12 cents per pound of excess
5,001–10,000 lbs over: 15 cents per pound of excess
Over 10,000 lbs: 20 cents per pound of excess

A vehicle 5,000 pounds over the restricted limit faces a fine of roughly $600; 10,000 pounds over runs about $1,500.⁵ The “limit” during frost-law season is the reduced limit, not the normal summer limit. A truck loaded to its normal legal weight and driven on a restricted road is already 25% or 35% over the seasonal cap, which can push the overage straight into the higher brackets.

How Enforcement Works

Michigan State Police Commercial Vehicle Enforcement officers patrol restricted routes and weigh individual axles at roadside inspections. If a vehicle exceeds the restricted weight, the officer can require the driver to shift or offload cargo on the spot before continuing.⁵ The violation is a civil infraction, and both the vehicle owner and the person who loaded the vehicle can be held liable, so shippers cannot pass the fine to the driver by default.

Enforcement tends to concentrate on county and local roads, which carry the 35% reduction and are more vulnerable to damage than state trunklines built to higher standards. Operators who try to route around weigh stations on back roads during frost-law season are often the ones who end up with both the inspection and the steeper fine.

1
Michigan Legislature. Michigan Compiled Laws 257.722 – Maximum Axle Load
2
Michigan Department of Transportation. Correction: Annual Spring Weight Restrictions Changing on Some Michigan Roads
3
Michigan Department of Transportation. Spring Weight Restriction Bulletins
4
Michigan County Road Association. Seasonal Weight Restrictions
5
Michigan Legislature. Michigan Compiled Laws 257.724 – Stopping Vehicle for Weighing; Shifting or Removing Load; Civil Fine and Costs