Frost Laws in Michigan: Spring Axle Limits and Truck Loads

The short answer

Michigan's frost laws are spring weight restrictions for trucks. While the ground under the roads thaws, the legal axle weight on "seasonal" routes drops by 25% on concrete (rigid) pavements and 35% on asphalt and other flexible pavements, and the allowed load per inch of tire width drops too. MDOT also notes a 35 mph maximum speed for some vehicles on those routes. All-season routes keep their normal limits. MDOT announces when the restrictions start and end each year, and county road commissions and cities set their own, which usually line up with the state's but not always.

For anyone who buys asphalt, gravel or topsoil by the ton, the practical effect is simple: a dump truck that normally hauls a full load may only be able to carry a fraction of it on a restricted road.

Why roads need frost laws

In a Michigan winter the soil and gravel under a road freeze solid, and frozen ground is strong. The trouble starts when it warms up. MDOT explains that frozen roads thaw from the surface downward, so the top layers soften while the ground deeper down is still frozen. Melting snow and ice soak into that softened layer, and the frozen soil below keeps the water from draining away. A roadbed full of trapped water cannot support heavy wheels the way it can in summer, and the pavement on top flexes, cracks and breaks into potholes.

The restrictions stay on until the frost has left the ground deep enough for the water to drain and the base to firm up again. That is why the end date moves around from year to year and from the southern Lower Peninsula to the Upper Peninsula.

Asphalt roads get the bigger cut because a stiff concrete slab generally spreads a wheel load over more of the base than a flexible asphalt layer does, so a soft base shows up sooner under asphalt. It is the same weak-base problem behind frost heave damage on driveways, just on a public road with loaded trucks on it.

Michigan frost law limits by axle

Michigan's truck weight law (section 257.722 of the Michigan Vehicle Code, as amended in 2024) sets the reductions, and MDOT's T-1 sheet on maximum legal truck loadings turns them into numbers. Here are the main rows from that sheet:

Axle type (spacing)	Normal limit	Spring, rigid (−25%)	Spring, flexible (−35%)
Single axle, 9 ft or more from the next axle	18,000 lb (20,000 lb if the vehicle is 80,000 lb gross or less)	13,500 lb	11,700 lb
Axle 3½ ft to under 9 ft from the next axle	13,000 lb	9,750 lb	8,450 lb
Axle in a tandem assembly	16,000 lb per axle (34,000 lb per tandem at 80,000 lb gross or less)	12,000 lb per axle	10,400 lb per axle
Axle less than 3½ ft from the next axle	9,000 lb	6,750 lb	5,850 lb
Load per inch of tire width	700 lb	525 lb	450 lb

The T-1 sheet labels the spring columns with a 35 mph speed limit. It also notes that on a legal combination, only one tandem assembly may run at the 12,000 lb (rigid) or 10,400 lb (flexible) per-axle figure, with other tandems held lower, so multi-axle trailers need a closer read of the footnotes. Vehicles operating within 5 miles of a special designated highway to reach a pickup or drop-off point on a restricted route must still come down to the spring single and tandem figures.

Notice the tire-width rule. It can be tighter than the axle limit, especially on a steer axle with two tires. Tire width means the rated size the manufacturer publishes, so check the sidewall rather than measuring the tread.

When frost laws start and end

The statute ties the reductions to March, April and May, but in practice MDOT decides the dates by measuring frost depth along state highways, watching road conditions and following the weather forecast. In 2026, for example, MDOT put restrictions in place at 6 p.m. on February 17 on state trunklines from the Indiana and Ohio borders north to a line running roughly along US-10 from Ludington to Clare and over to Standish, then lifted the last of them statewide at 7 a.m. on May 15.

The law also requires MDOT and every local road agency that applies the restrictions to post the dates and the affected roads on its website, or on a statewide road association's site if the agency has none. MDOT publishes numbered Spring Weight Restriction Bulletins each season and runs a recorded line at 1-800-787-8960. To see which state highways are seasonal and which are all-season, use the MDOT Truck Operators Map: green and gold routes are all-season, solid or dashed red routes are seasonal. For county roads and city streets, check the county road commission or the city's public works department, and watch for posted signs.

Who is exempt

Under the 2024 version of the statute, the spring reductions do not apply to:

Vehicles hauling agricultural commodities, subject to conditions in the law.
Public utility vehicles on local roads, also with conditions.
School buses.
Propane trucks making residential deliveries with the tank no more than 50% full and traveling no faster than 35 mph.

Construction materials are not on that list. A load of hot mix, crushed stone or sand on a seasonal road plays by the reduced numbers. MDOT also stops issuing single-trip permits for overweight loads, and for loads over 14 feet wide, 11 axles or 150 feet long, on restricted routes during the restriction period.

Worked example: a tandem dump truck in spring

Here is what the rules do to a typical three-axle dump truck (a steer axle plus a rear tandem) hauling asphalt. The axle limits come from the T-1 table above. The truck details are assumptions for illustration only: an empty weight of 27,000 lb, two steer tires rated 12 inches wide, eight rear tires rated 11 inches wide, and a gross weight under 80,000 lb. Your hauler's real numbers will differ.

Item	Normal season	Spring, concrete route	Spring, asphalt route
Steer axle limit	20,000 lb	13,500 lb	11,700 lb
Steer tire limit (2 × 12 in × lb/in)	16,800 lb	12,600 lb	10,800 lb
Steer axle allowed (lower of the two)	16,800 lb	12,600 lb	10,800 lb
Rear tandem allowed	34,000 lb	24,000 lb	20,800 lb
Total allowed	50,800 lb	36,600 lb	31,600 lb
Minus empty truck (assumed)	27,000 lb	27,000 lb	27,000 lb
Legal payload	23,800 lb (11.9 tons)	9,600 lb (4.8 tons)	4,600 lb (2.3 tons)

On an asphalt road under frost laws, this truck loses more than 80% of its payload, because the empty truck itself uses up most of the reduced allowance. That is the real reason spring deliveries cost more and take more trips: the truck still weighs the same, but the road will carry less on top of it. In practice the load also has to be spread so no single axle goes over its own limit, which a scale ticket will show. For the normal-season picture, see how many tons of asphalt fit in a dump truck.

What that means on the ground: at a 2-inch compacted depth and a planning density of 145 lb per cubic foot, one ton of hot mix covers about 83 square feet. So the normal 11.9-ton load paves roughly 985 square feet, while the 2.3-ton spring load on an asphalt route covers only about 190 square feet. A small driveway that one truck could handle in June might need four or five trips in April. Run your own job through the how many tons of asphalt calculator to see how many loads you need.

Why the cut is bigger than it looks

Pavement damage climbs much faster than axle weight. Engineers express that with the equivalent single axle load (ESAL), and a common rule of thumb says damage rises with roughly the fourth power of the axle weight compared with an 18,000 lb axle. By that approximation, an 11,700 lb axle does about 18% of the damage of an 18,000 lb axle on a healthy road, and a 13,500 lb axle about 32%. It is a rough guide, but it shows why a one-third cut matters when the base is at its weakest.

How other states handle it

Michigan is not alone. Minnesota calls its version spring load restrictions. MnDOT starts them when its cumulative thawing index for a frost zone is forecast to pass 25 degree-days Fahrenheit and longer-range forecasts call for continued warmth, a threshold based on deflection and frost-depth measurements at the MnROAD test site. During the restriction period Minnesota limits single axles to 5 tons on unpaved roads and 10 tons on paved roads unless signs say otherwise, and some routes are posted at lower limits such as 7 tons. Minnesota also allows winter load increases while the ground is frozen hard, the reverse of the spring rule.

Tips for spring paving and material deliveries

Ask your supplier about the route. The plant, quarry or contractor knows which roads between them and you are seasonal. A short detour onto an all-season route can mean a fuller truck.
Expect smaller loads and more trips. Smaller loads usually raise the cost per ton. Our guide to asphalt hauling cost per ton explains how delivery pricing works.
Wait if you can. Work that can wait until restrictions lift gets fuller trucks.
Check the tires. Owners of their own dump trucks or trailers should read the rated tire width on each sidewall and do the 450 or 525 lb per inch math, since it may be the tighter limit. Keep a heavy-duty dual-head truck tire gauge in the cab to keep tires at their rated pressure.
Plan routes ahead. MDOT's map is the authority for Michigan, but a printed trucker's atlas such as the Rand McNally Motor Carriers' Road Atlas helps with low clearances, weigh stations and restricted routes when you are planning trips out of state.

Frost laws FAQ

What are frost laws in Michigan?

They are seasonal weight restrictions that lower legal truck axle weights while roads thaw in spring. On seasonal routes, Michigan cuts axle limits by 25% on concrete pavements and 35% on asphalt and other flexible pavements, and lowers the allowed load per inch of tire width to 525 and 450 pounds.

When do Michigan frost laws start and end?

The statute ties them to March, April and May, but MDOT sets the actual dates each year from frost-depth readings, road conditions and forecasts. In 2026 MDOT started them on February 17 in the southern Lower Peninsula and lifted the last ones statewide on May 15.

Do frost laws apply to all roads?

No. MDOT all-season routes, shown in green and gold on the Truck Operators Map, keep normal axle limits. Seasonal routes, shown in red, are restricted. County road commissions and cities set their own restrictions and post signs.

Who is exempt from frost laws in Michigan?

Under the 2024 statute, school buses, vehicles hauling agricultural commodities and public utility vehicles on local roads (both with conditions), and residential propane deliveries with the tank no more than half full at 35 mph or less are exempt.

How much less can a dump truck haul during frost laws?

It depends on the truck, but the cut comes out of the payload. In our example, a tandem dump truck with an assumed 27,000 lb empty weight drops from about 11.9 tons of legal payload to about 2.3 tons on a restricted asphalt route.

The bottom line

Michigan's frost laws protect thawing roads by cutting truck axle weights 25% on concrete routes and 35% on asphalt routes, with tighter tire limits and a 35 mph speed cap. MDOT and local road agencies set the dates each spring from frost-depth readings and post them online. For a dump truck, the cut comes almost entirely out of the payload, so a spring asphalt or gravel delivery can carry a small fraction of a summer load. Check the route, ask your hauler early, and if the job can wait until the restrictions lift, it will usually cost less.

Sources checked for this article

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