Frost Laws by State

How do frost laws work?

Frost laws cover the few weeks when a road is weakest. WisDOT's own explanation: in spring the ground thaws from the pavement surface down while frost can still reach 48 to 72 in below it, so meltwater cannot drain through the frozen layer and the base under the asphalt turns unstable. Sun on asphalt can push pavement temperatures into the 50s while the air sits in the 20s and 30s, and the road refreezes at night. Heavy axles on that wet base crack and break the pavement.

That is why the dates come from measurements, not the calendar. WisDOT declares Class II restrictions zone by zone when the thaw reaches 6 in below the pavement. MnDOT schedules spring load restrictions when the 3-day forecast thawing index passes 25 F degree-days and aims to keep them to 8 weeks or less. NDDOT uses temperature probes in the road base and deflection testing, and says the worst damage happens in the first 4 weeks after the thaw begins.

The restriction itself takes one of four forms, and one trip can meet all of them:

• Percentage cuts. Michigan reduces axle loads 25% or 35% (MCL 257.722(8)). Ohio lets ODOT cut weight or speed up to 25% on state highways and counties up to 50% (ORC 5577.07).
• Tons per axle. Minnesota 10 tons on paved and 5 tons on unpaved roads; North Dakota 8, 7, 6 or 5 tons; South Dakota 6 or 7 tons; Wisconsin's posted segments 6 tons single axle, 10 tons tandem, 24 tons gross.
• Tire-width or per-tire caps. New Hampshire allows 300 lb per inch of tire width up to 30,000 lb gross; Michigan 525 or 450 lb per inch; Washington caps each tire by size, such as 4,000 lb on an 11-22.5 tire.
• Permit suspensions. Michigan issues no overweight single-trip permits in its restricted area, Montana none on restricted highways, and Wisconsin keeps overweight-permit vehicles off its Class II roads.

Michigan frost laws

Michigan's seasonal weight restrictions are written into MCL 257.722(8): during March, April and May, maximum axle loads drop 25% on concrete pavements and concrete-base roads and 35% on all other roads, and wheel loads drop from 700 lb to 525 or 450 lb per inch of tire width. MDOT or a local road agency can start them earlier or suspend them (257.722(10)), and MCL 257.627(3) holds trucks of 10,000 lb or more to 35 mph while the reduced loadings are enforced. MDOT sets state trunkline dates from frost-depth readings, road conditions and forecasts; county road commissions and cities set their own.

How much weight Michigan's frost law takes off

Seasonal columns from MDOT's 2026 Truck Operators Map table "Seasonal Load Limitations (Speed Limit 35 mph)". Rigid means concrete or a concrete base; flexible means bituminous surfaces on a gravel base.

By our arithmetic from that table, a tandem that carries 16,000 lb per axle in summer drops to 12,000 lb per axle on a solid-red route and 10,400 lb on a dashed-red route: 8,000 to 11,200 lb less on that pair before the rest of the trailer is counted. Overweight is a civil infraction with per-pound fines that start at 3 cents per pound and reach 20 cents per pound when the excess is over 10,000 lb (MCL 257.724(3)).

Will there be a frost law in Michigan in 2026?

Yes, and it is over. MDOT's Bulletin #1 imposed restrictions at 6 p.m. on February 17, 2026, and Bulletin #8 lifted the last of them at 7 a.m. on May 15. As of October 17, 2026, no seasonal weight restrictions are in effect: MDOT's latest bulletin is #8 (May 15, 2026, season completed), and the County Road Association map shows all 83 counties with no restriction in effect. The next season starts when MDOT's first bulletin says so; from 2019 to 2026 that bulletin came between February 2 and March 11, and the final statewide lift between April 15 and May 15.

Michigan frost law map and hotline

There are two maps. MDOT's 2026 Truck Operators Map shows all-season routes in green (Special Designated Highways) and gold (National Truck Network), where legal axle weights are not reduced, and seasonal routes in solid red (rigid pavement, 25% cut) or dashed red (flexible pavement, 35% cut). County roads are on the County Road Association of Michigan's statewide map, which shows each of the 83 counties' status, its all-season and restricted road lists and permit links. MDOT's weight restriction hotline is 800-787-8960; carriers based in New Jersey or Canada call 517-373-6256.

County calendars run on their own: in 2026 Kent County imposed restrictions on January 10 for an early thaw, and Marquette County kept them until May 18, three days after MDOT's final lift. 2026 county dates we confirmed:

• Kent: Jan 10 (early thaw), suspended Jan 19, re-imposed Feb 16, lifted Mar 30
• Washtenaw: Feb 17 to Mar 23
• Oakland (RCOC): Feb 18 to Mar 25
• Livingston: Lifted Apr 1
• Grand Traverse: Lifted Apr 14
• Marquette: Lifted May 18, three days after MDOT's final lift

Permits during Michigan's restrictions

In the weight-restricted area MDOT issues no single-trip permits for overweight loads or for loads over 14 ft wide, 11 axles or 150 ft long, and extended permits are valid for oversize only; a public emergency is the exception (MDOT T-2). MDOT permits never cover county roads or city streets, so a county leg needs that county's permit, and some counties suspend their own oversize and overweight permits while restrictions are on (Kent County did on January 10, 2026). An overweight machine bound for the restricted area waits for the bulletin that lifts it.

What are the frost laws in Wisconsin?

Wisconsin runs three programs, all on state highways only. The frozen road declaration (Dec 14, 2025 to Feb 20, 2026 in Zones 1 and 2; Feb 6 to Feb 20, 2026 in Zones 4 and 5) lets trucks hauling forest products cut crosswise or road salt exceed normal gross limits with no permit. In spring, Class II highways, about 1,400 miles (94 segments, 12% of state highways), close to overweight-permit vehicles, and about 170 miles (13 segments, under 2% of state highways) are posted at 6 tons single axle, 10 tons tandem, 24 tons gross (Wis. Stat. 349.16). Most divisible-load multiple-trip permits are suspended statewide during the thaw; raw forest products permits at 98,000 lb and potato seed permits continue.

Dates from WisDOT's Class II Roadway Weight Restriction History; averages are WisDOT's for 2015 to 2026.

Overweight non-divisible permits are not restricted in Milwaukee County or on the Interstate system, and annual non-divisible permits still work on Class I roads. Local roads are the catch: annual permits are not valid on county and town roads during the thaw unless the carrier gets a single-trip permit from the local road authority. WisDOT's recorded status line is (608) 266-8417.

Indiana and Iowa frost laws are mostly county rules

We found no INDOT frost program in Indiana. IC 9-20-1-3 lets counties, cities and towns restrict their roads for up to 90 days a year, effective only once signs stand at each end. Each county writes its own rule: Newton County bars vehicles over 5 tons from county roads February 1 to April 1, Jasper County caps gross weight at 16,000 lb January 15 to April 15, and Porter County limits single axles to 10 tons, tandems to 15 tons and tri-axles to 20 tons when it declares a frost law. In 2026 LaPorte County's frost law ran only from February 16 to 23. State permits do not cover county roads; LaPorte and Porter sell frost-law permits at $100, and Newton issues none.

Iowa splits the job. Counties and cities may embargo roads for up to 90 days a year (Iowa Code 321.471); in 2026 Linn County set a 5-ton embargo on its secondary roads except paved ones. Iowa DOT restricts selected primary highway segments each spring for all trucks over 80,000 lb (2026 map dated March 6) and answers status calls at 515-237-3268 from February 1 to May 30. An Iowa oversize or overweight permit does not waive an embargo unless it says so (761 IAC 511.2(4)).

How frost laws change a heavy haul plan

For general freight a frost law means lighter loads on seasonal routes. For heavy haul it can mean no permit at all, because the loads that need overweight permits are the ones the restrictions target. For heavy haul transport between February and May in the northern states, the plan changes in three places: when the load moves, which roads it uses and which permits are possible.

Time the move

NDDOT's own advice is to move overweight loads before restrictions are placed. Michigan's first bulletin has come between February 2 and March 11 since 2019, and its final lift between April 15 and May 15. Minnesota reopens middle-range permits on the day a zone lifts but full summer permits only 2 to 3 weeks later, so a load that needs full summer axle weights waits longer than the lift date suggests.

Route around the posted roads

Restrictions are not uniform along a route. Michigan's green and gold all-season routes keep legal axle weights, Minnesota's Interstates carry full summer weights for through trips, and Wisconsin does not restrict non-divisible permits in Milwaukee County or on Interstates. The delivery leg is where plans fail: county roads often stay restricted after the state lifts, as Marquette County's did until May 18, 2026. Start from axle-by-axle weights; our bridge formula calculator shows what each axle group may carry at legal weight, and the seasonal posting then cuts from that number.

Permits during the season

Expect fewer permits, not more. Michigan and Montana issue no overweight permits on restricted highways, Wisconsin bars overweight-permit vehicles from Class II roads, and Minnesota issues them only when every axle is legal. In Michigan, Minnesota and Indiana a state permit does not cover county or town roads at all, so each county on the route issues its own permit or none. Our guide to oversize permits by state covers the normal permit rules, the legal load limits page explains when a load becomes overweight in the first place, and the oversize load checker shows which states need permits and escorts for a load's size and weight.

Spring farm equipment moves

Planting season overlaps frost season. Iowa exempts implements of husbandry and implements hauled for repair from county embargoes (Iowa Code 321.471). Michigan's farm exemption is written for vehicles hauling agricultural commodities and needs 48 hours' notice to the county road commission (MCL 257.722(5)). Minnesota's seasonal statute (169.87) lists no general farm exemption. A tractor or planter on a lowboy is still a heavy axle load, so farm equipment transport in March and April gets the same route check as a dozer.

How we plan a move in frost-law season

1. Get axle weights and spacings, not just the gross. Michigan, Minnesota and the Dakotas write their limits per axle; New Hampshire and Washington per inch or per tire.
2. List every road authority on the route (state DOT, each county, each town or township) and check its current status: MDOT bulletins, MnDOT zone dates, WisDOT zones, county maps.
3. Pick the plan: move before the first bulletin, stay on all-season or Interstate routes, spread the load over more axles, or wait for the lift and the permit reopening.
4. Order state permits through each state's system once the route clears the restricted areas, and local permits separately where counties issue them.
5. Recheck the day before loading. WisDOT gives at least 24 hours' notice and MnDOT at least 3 days, and county roads change on their own schedule.

HTS Logistics is a licensed property broker (MC 1178470) in East Northport, New York. We plan moves around these restrictions, order permits through each state's system and book a carrier whose trailer fits the axle limits on the route.