Frost Laws & Seasonal Weight Restrictions
Last reviewed September 2026
Every spring, roads across Canada and the northern United States temporarily lose a share of their legal capacity. As frost leaves the ground, the roadbed softens, and a weight that pavement carries easily in January will destroy it in March. Frost laws, also called spring weight restrictions or half-load season, are the annual response, and they are one of the most underestimated schedule risks in heavy freight.
Why thawing roads lose strength
Frozen ground is structural: ice binds the road base into something close to rock. During thaw, meltwater is trapped between the softening surface and still-frozen layers beneath, and the roadbed turns spongy. Axle loads that would be legal year-round pump that water through the base and break the pavement from below. Restricting weight for a few weeks costs far less than rebuilding the road, so jurisdictions restrict.
How restrictions work
During the restricted window, posted roads drop to a percentage of their normal axle limits, commonly expressed as reduced load periods or half-load limits. Primary highways built to full depth often stay unrestricted while secondary and municipal roads post reductions, which matters because the last mile to a farm, mine, or rural jobsite is usually exactly the road that posts. Overweight permits are often suspended or tightened on restricted roads for the duration.
When and where
Windows follow the climate, not the calendar: restrictions typically begin between late February and April and lift between May and June, announced by each jurisdiction each year, sometimes zone by zone as the thaw moves north. Northern jurisdictions may also RAISE limits in deep winter, when frozen roads temporarily carry more than their summer rating, a winter-weights premium the resource industries plan around.
Planning shipments around thaw
If your load is heavy and your window is flexible, shipping before the thaw or after the lift can be the difference between a routine move and a re-routed, re-permitted one. Dispatch checks current restriction orders on every heavy move during the season; if your delivery point sits on a posted road, we tell you before booking, not at the town line.
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Get an instant quote →Common questions
Do frost laws affect normal-weight freight?▾
Usually not: a legally loaded five-axle at normal limits clears most restrictions. The exposure starts with heavy single items, dense freight, and anything already near axle limits.
Are the dates the same every year?▾
No. Each jurisdiction declares start and end dates yearly, by weather, and can vary them by zone. That is why we check current orders rather than a calendar.
Can a permit override a frost restriction?▾
Sometimes, at reduced weights, with conditions, and sometimes not at all; posted municipal roads are often absolute. It is a route-by-route answer that dispatch resolves during planning.
This guide is provided free, for general information, so shippers can see how oversize and overweight moves work. It is not legal advice and not a permit determination. Limits, escort bands, fees, and seasonal restrictions change regularly; before relying on any figure, verify it with the jurisdiction's transportation department or permit office, or a licensed permit service. When you book with LoadLoom, our dispatch desk and your assigned carrier confirm the current rules for your exact load and route; that confirmation, not this page, governs your shipment. Spot an error? Email customercare@loadloom.com.