Frost heaving and weight limits
Frost heaving is a problem that arises on gravel roads in the spring. Due to the warming climate, surface frost heaving is also common in the autumn, and in Southern and Central Finland it can even be seen in winter.
In the spring, when the ground frost melts, the roads are at their most vulnerable; frozen water inside the structure of the road starts to melt, but it cannot evaporate or flow out quickly enough. The water in the structure weakens the load-bearing capacity of the road, and if a lot of heavy vehicles pass along the road at these moments, the road can give in completely.
This phenomenon caused by the melting process is called frost heaving. Frost heaving is a familiar problem on gravel roads, but the same principles also apply on paved roads. As the climate changes, these problems on paved roads are also increasing.
Water may also enter road structures in the autumn – and due to the warming climate even in winter – because the structures do not freeze as a result of heavy rainfall and poor drainage conditions. This leads to surface frost heaving which softens the road surface, weakens its load capacity, and worsens drivability.
It is important that heavy transports are carried out in good time before the frost heaving season. For example, builders should anticipate the imposition of weight restrictions and obtain the supplies they need before the frost heaving begins. The surest approach is to purchase supplies such as building materials already in the winter, otherwise it may take a long time to get them on site in the spring.
It is necessary to set weight limits for some of the roads that experience frost heaving. This helps to prevent excessive damage to roads by heavy traffic and ensures access for essential transports. The most commonly used weight limit is 12 tonnes, with a 4 tonne weight limit only being applied in exceptional cases. Weight limits do not apply to vital transports.
Vital transports include:
- Emergency vehicles
- Road maintenance vehicles
- Coaches and mobile libraries on their scheduled routes
- Commuting (commuting to the work site in an empty heavy-duty vehicle)
- Milk transports
- Regular and essential transports of peat, fuel wood and other similar transport services for the daily operation of energy plants
- Transport of slaughtered animals
- Transfers of heavy agricultural machinery related to spring sowing and transport of seed grain, fertilisers etc between the farm and the fields
- Transport of animal feed and peat bedding (where consumption in relation to the size of storage facilities does not allow for advance transports)
- Collection of household waste (organised by the municipality, based on legislation and operating according to the agreed schedule)
- Farm-specific transport of liquid manure
- Daily goods transport to shops
- Mobile shops
Forecasts on the need to set weight limits are made around the turn of the year The forecast is revised at the beginning of March once the forecasts on the extent of frost heaving problems have been prepared. The weather conditions in the spring are monitored actively, and regular communications are provided on the development of frost heaving and the need for weight limits.
In individual, unforeseen cases, the ELY Centre may grant, subject to a fee, a temporary transport permit for a road with a weight limit. The necessity and weight of the transport are taken into account in the permit process, and the permits are granted by the ELY Centre for the area in question. The processing of the permit application takes a couple of working days. The price of the permit is EUR 110. (Permit application form).
List with examples of transports for which an exemption permit is required:
- Soil materials
- Industrial fertilisers for farms
- Building supplies
- Forestry and construction machinery
- Special transports