Frost Laws And Spring Weight Restrictions By State

What Is A Frost Law?

When the ground thaws from the top down, melt water is trapped above the still-frozen layer and the base under the pavement loses strength. Heavy axles then break up the road. States respond with seasonal limits: lower legal weights on weaker roads, fewer overweight permits, and in some states a winter weight increase before the thaw, while the ground is frozen hard.

Each state decides its own dates. South Dakota tracks daily freeze and thaw indexes along with field observations, and North Dakota uses computer modeling checked by temperature probes under the road. That is why no calendar date holds from one year to the next.

Which States Have Frost Laws, And When?

These states publish seasonal restrictions on state highways. Dates in the table are the 2026 season where the state published them; check the 2027 notice before you plan.

Other northern states, and many counties in states not listed, post roads too. A permit for a state highway does not cover a posted county or town road.

How Do Frost Laws Affect An Oversize Permit?

Michigan is the strictest for dimension loads. Each 2026 spring bulletin said:

“Single trip permits will not be issued for overweight loads or loads exceeding 14 feet in width, 11 axles and 150 feet in overall length in the weight restricted area.”

Extended permits stay valid for oversize only inside the restricted area. Routes MDOT designates all-season keep normal axle weights.

Wisconsin suspends most divisible-load permits on all state highways during the thaw, and overweight non-divisible single-trip and multiple-trip permits must stay off Class II highways: about 1,400 miles in 94 segments. Non-divisible permits are not restricted on the Interstate system or in Milwaukee County.

Minnesota lowers weights on restricted roads, then brings heavier overweight permits back in two steps: middle-range permits when a zone’s restrictions lift, and full-summer permits about two to three weeks later. In 2026 that was April 20 and May 8 for the Metro, South and Southeast zones, and May 15 and June 1 for the North zone.

An oversize load at legal weight usually rides through frost season untouched. An overweight load may need a different route, a lighter configuration or a later date.

Where Does RouteAll Fit?

RouteAll does not track seasonal postings. Upload your permit and it lists every road it read, so you can check each one against the state’s frost map, then warns you if you leave them.

Before You Roll: Planning Around Frost Laws

• Subscribe before February. Minnesota, North Dakota and South Dakota offer email alerts; Michigan numbers its bulletins.
• Check every state and every county on the route. Wisconsin and South Dakota both say local road authorities set their own limits, and Maine lets towns post local roads.
• Use the state map. Michigan’s Truck Operators Map marks seasonal routes in red and all-season routes in green or gold.
• Move heavy loads early. North Dakota’s DOT advises moving overweight loads before restrictions start.
• Re-check after the lift. A state lifting its restrictions does not lift a county’s or town’s.

Common Questions

When do frost laws start?

Usually between mid-February and March, set each year from frost and thaw measurements. Michigan’s 2026 restrictions began February 17; Minnesota’s began March 3 in its southern zones. South Dakota law allows restrictions any time from February 15 to April 30.

Do frost laws apply to oversize loads?

Mostly to weight. A load at legal weight is usually unaffected, but Michigan issues no single-trip permits in its restricted area for overweight loads or loads over 14 feet wide, 11 axles and 150 feet long, and Wisconsin keeps overweight non-divisible permits off Class II highways.

How do I find out if frost laws are in effect?

Check the state notice: MnDOT’s load-limits page, MDOT’s spring weight bulletins, WisDOT’s seasonal map, North Dakota’s travel map and 511, and SD511’s CVO restrictions. Then check each county on your route, because local roads are posted separately.