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Thaw - load restrictions

Each spring, the Ministère determines the thaw period dates for the three Thaw Zones across Québec. During this time, heavy vehicles travelling on the road network must reduce their loads, in accordance with the limits imposed by the Vehicle Load and Size Limits Regulation.

During periods of thaw, the road is 30 to 70% more fragile than usual. A single overloaded vehicle can cause substantial damage. However, a slight reduction in load significantly decreases damage to the pavement. This is why load restrictions are imposed on heavy vehicles during periods of thaw. These restrictions generally range from 8 to 20%.

Thaw periods are determined after monitoring the progress of thaw on the pavement. This is done using sensors across the Québec road network. Weather forecasts are also taken into account.

Normative framework

Section 419 of the Highway Safety Code (c. C-24.2) allows the Minister, by an order published in the Gazette officielle du Québec, to determine the locations where the movement of all or some road vehicles is restricted or prohibited due to thawing, rain, erosion or flooding. The Minister also determines the periods during which these measures apply.

Section 621 of the Highway Safety Code allows the Government to regulate the loads and sizes of vehicles travelling on Québec roads.

The Vehicle Load and Size Limits Regulation combines various standards that limit the size, loads per class of axles, and total loaded mass of the road vehicles travelling on public roads.

During thaw periods, this regulation stipulates load restrictions that apply based on three geographic areas

Target clientele

Users, owners and drivers of heavy vehicles, shippers and transportation intermediaries.

General information

Spring thaw: a critical period

Everyone knows that weather conditions in Québec are particularly harsh. The ground freezes to a depth of 1.2 to 3 metres for more than four months out of the year. This factor, combined with changes in temperature and humidity, has a major impact on pavement behaviour. Freeze-thaw cycles also contribute to making pavement more vulnerable.

Longitudinal section of a roadway undergoing deformation caused by the passage of a loaded wheel. Graph showing the variation in a roadway’s load bearing capacity according to the progression of the freeze-thaw cycle. 

In spring, the layers of materials that make up the pavement are weakened by the accumulation of water. Studies conducted by the Ministère pertaining to the bearing capacity of roads have demonstrated that the reactions of the pavement under a load at this time are 50% to 70% more pronounced than those recorded during the summer.

At any given time, a vehicle that is overloaded by 25% will increase the level of damage by 150%. This phenomenon is magnified during thaw periods, and the same axle load can create a tensile strain that is 5 to 8 times greater than at other times.

The impact of heavy vehicles during thaw periods is therefore considerable, given that the number of commercial vehicles has increased significantly over the last 25 years. This is why regulations require carriers to reduce their loads.

Reduction in road vehicle loads

To protect the Québec road network, the Ministère has adopted the Vehicle Load and Size Limits Regulation. This regulation limits the class of axles load and total loaded mass of road vehicles and combinations of road vehicles. It states the more restrictive load limits applicable during thaw periods.

Information on load standards during thaw periods can be found in the Road Vehicle Load and Size Limits Guide. Information can also be obtained through the Contact us section of the Ministère’s website.

Load checks during thaw periods

Contrôle routier Québec officers, who report to the Société de l’assurance automobile du Québec (SAAQ), ensure that heavy vehicles comply with load restrictions. For these 300 or so traffic controllers, who operate across the province, the spring thaw is a time of intensive weighing operations.

To prevent accidents and adequately protect roadways, these officers enforce strict compliance. Therefore, in keeping with this policy, any vehicle that is overloaded or that presents a risk may not get back on the road until to complies with regulations. When a truck is overloaded, the driver must distribute the load over the axles or unload the excess weight before getting back on the road. An overloaded truck not only damages the roadway, but its road behaviour is also affected, thus making it less safe. Compliance with vehicle load limits is crucial, and the SAAQ is intensifying its efforts in this area, as the protection of roadways has been retained as a control priority.

During thaw periods:

  • There is a greater number of road checks;
  • In cases of overload, all heavy-vehicle drivers must distribute the load over the axles or unload the excess weight before getting back on the road.

More information on road transport control can be obtained by contacting the information centres of the Société de l'assurance automobile du Québec.


Frequently asked questions

During the thaw period, roads are 30% to 70% more fragile than during normal periods, so why are load reduction only 8% to 20%?

Damage to the road network is caused by several factors. Among these factors, the load under the wheels of a heavy vehicle has a huge influence. The relationship between the load and the damage is not linear, but rather exponential, which means that a slight overload will have a significant effect on the damage that may be caused to a road network. For example, a 20% overload on a single axle causes twice as much damage to the road as a legal load on the same axle. Conversely, a slight decrease in the authorized load results in a significant decrease in its effect on the road network. Therefore, a 20% reduction corresponds to a reduction in damage of approximately 60% compared to an axle that bears a legal load. Load reductions that are applicable during the thaw period have been staggered in order to maximize the protection of the road network while ensuring that economic activity in sustained.

Why is Québec divided into three load restriction zones during the thaw period?

The thaw zones were established by taking into consideration differences in the frost depth, which varies considerably from north to south, the progress of the thaw, the climatic conditions that are prevalent in the various regions of Québec during the spring, the geographic characteristics of the province, and heavy vehicle traffic in the east-west corridor. Obviously, it would be possible to increase the number of zones in order to take into consideration the microclimate specific to a given area to a higher degree. By doing so, the duration of the period of load restrictions in each zone could be reduced. However, inter-zone truck transport would become very constricting, which would severely restrict mobility.

Why are the weigh stations that are located along the roads not open 24 hours per day all year long?

Check stations are operated according to a sporadic opening strategy, depending on the season, the days of the week, the time, the type of transportation and the class of roads where the check station is located.


In the thaw period, depending on the traffic flow of the road where they are located, the check stations are open 4 to 8 hours a day, on the average. Some of them can remain open up to 24 hours a day, according to a synchronism that accounts for the neighbouring check stations. This approach ensures optimum coverage of the main road corridors. Contrôle routier Québec also relies on a mixed strategy, including both interventions at fixed stations and mobile interventions, particularly by creating temporary control areas.

Where do potholes come from, and how are they formed?

Potholes represent the final step in a series of surface deterioration phenomena on a pavement.

Events occur in the following sequence:

  • Appearance of cracks, which may have been caused by a number of factors, including intense traffic, the freeze/thaw cycle, production defects, etc.;
  • Deterioration of the cracks due to a concentration of constraints under the effect of traffic, and the appearance of multiple cracks;
  • Infiltration of water and brine, which contributes to a reduction in the bearing capacity of the foundation and the acceleration of the deterioration process;
  • The freeze/thaw cycle accelerates the deterioration;
  • The effects of traffic: dynamic impacts, the number of vehicles, and the severity of the phenomena described above are all factors that determine the rate at which potholes appear.

Given the climatic conditions in Québec, is it possible to avoid the appearance of potholes?

Generally speaking, the formation of a pothole is closely related to the state of the pavement. Therefore, the risk of a pothole appearing is related to the degree of cracking of the coating, traffic use, and the amount of water that is liable to penetrate beneath the coating. Maintenance work to keep the pavement in good condition is the best way to prevent the formation of potholes.

In light of this, it is possible to prevent the appearance of potholes if pavements are adapted to local weather conditions, if they are not subjected to a more intense traffic condition than they were designed for, and if it is possible to maintain them adequately within the necessary timelines.

It is important to remember that the restrictions that are placed on the loads carried by heavy vehicles during the thaw period are not intended to ensure the protection of the driving surface, which is affected by all vehicles (for example, a road in a residential district where heavy trucks do not drive may be covered in potholes), but rather to preserve the actual structure of the road.

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