2020 Frost laws introduction and overview.
Frost/thaw damages to surface.
2020 frost laws, seasonal load weight and speed restrictions by State/Province (USA and Canada).
Section 1. The United States: Restrictions and guidance on seasonal weight restriction laws.
Many states incorporate temporary special weight limits and restrictions (frost laws) during the spring months of the year. These temporary restrictions are usually referred to as “frost laws” and implemented typically during the month or March and April. In some Northern States and Provinces frost laws can still be in effect in July as it’s much colder in the North. Since these restrictions are implemented on a “as needed” basis it is possible many of the official government websites may not have published this temporary restriction in a convenient place as frost laws are also subject to change at any moment based on the temperature of the roads core. You want to be certain to check with the appropriate department officials to verify the latest changes in the laws.
It is very typical for States and Provinces to not be clear about their exact weight requirements during frost law season. This gives them the opportunity to examine each proposal individually on a case-by-case basis to determine if any damages may occur at the time should the shipment be approved. Information may only be available by contacting the SPECIFIC DEPARTMENT. The axle weight limits and spacings are determined by many factors including road conditions, temperature, moisture content in the soil, etc. Note multiple weight limits can be in effect at the exact same time in different parts of the region due to temperature as well as the actual construction of the road.
Visit any of the links below to view state frost laws:
Section 2. Canada: Restrictions and guidance on seasonal weight restriction laws.
Many Canadian provinces issue spring frost law weight restrictions in the month of March and current Province websites may not be all inclusive of temporary changes in their laws. It is wise to check with the province’s DOT office (or appropriate department) for the most current and latest frost law information.
Visit any of the links below to view province frost laws:
Protection of our roads and highways.
There’s a delicate balance between protecting roadways during the spring thaw. In order to keep the trucking industry operating the Northern US states and Canadian provinces rely on engineers and scientific data to determine which dates frost laws will be in effect. With fairly recent advances in science and technology, data is much more reliable. This helps with the implementation of “Frost Laws” or “Seasonal Weight Restrictions” ensuring they are not implemented to early or late. While no State or Province desires to delay the transportation of goods through their territory it is imperative public assets are protected.
In areas that constantly get negative temperatures the amount of damages has forced Northern US States as well as Canadian Provinces to create and enact laws that restrict vehicle weights during spring months (specifically trucking companies), when the roads and bridges are thawing. There are all kinds of things that can go wrong with different types of roads and pavements. For example the State of Michigan has implemented permanent frost laws that go into effect during the months of March through May (and in some cases even June). Some routes require the legal axle weight limits be decreased by as much as 35%. Some States and local governments may also limit heavy-haul vehicle speeds to a maximum of 35 miles per hour during the frost law months regardless of posted limits.
Most major highways are constructed in 3 layers. The top layer you see or the pavement usually averages about 4″ to 6″ in thickness depending on it’s age. This layer of pavement is supported by 2 more layers. One is called the base layer and the other a sub-base layer. Together these three layers are typically at least 36″ in depth with most much more thicker. For instance in Southern Oregon on old US Highway 1 which follows the coast line from Mexico to Canada the road is a much as 16 feet thick as years of pavement has been laid. It should be noted that today’s technology is able to provide us with roads that are flexible due to the engineering of the construction process and the materials used. Excessive weight exerted by overloaded axles (or a weakened supporting base) can cause the pavement to bend or deform. The strength of the road combined with its resistance to bending determines the amount of weight the roadway can handle.
Road building technology has improved significantly during the last decade. The most obvious winter damage is the occurrence of potholes that are the result of moisture in the pavement freezing and weakening the top layer of the road. However, modern road building materials significantly reduce the amount of moister retained in the top layers, reducing the occurrence of pot holes. The base and sub-base however are still subject varying amounts of moisture that is influenced by rain, run-off and general moisture content during the spring months.
Roadways are built to carry normal maximum axle and gross weights based a certain level of residual moisture in the layers of the road bed. During the normal winters in the northern states and Canadian provinces, water in the soil typically freezes down to depths of a meter or more, preventing excess water from escaping. In fact, some areas in Canada allow up to a 25% increase in axle and gross weights because the solidly frozen base layers strengthen the road structure. During the spring thaw, however, axle and gross weights may be reduced by as much as 35%.
What exactly are frost laws?
Frost laws are seasonal restrictions on traffic weight limits and speeds on roadways subject to thaw weakening.
During the spring thaw, the roadbed is softened by trapped moisture beneath the pavement, reducing the supporting strength of the road to less than the original construction strengths. As the excess moisture evaporates or drains away, the road bed will stabilize and return to normal design strengths.
Because of the variability of temperatures each year States and Provinces must manage maximum weight and speed restrictions on a seasonal basis to both protect and preserve roads and ensure maximum access to trucking interests.
“Seasonal weight restrictions” typically start in early March and continue through mid-June. Since conditions vary from year to year, from below-normal to above-normal temperatures, most states and provinces reserve the authority to adjust spring load restrictions based on observed seasonal rain and temperature conditions, weather forecasts, as well as soil moisture sampling, to determine the dates for setting and removing weight restrictions. Weight restrictions remain in effect until sufficient moisture has escaped and the roadbeds regain stability. The most significant pavement damage occurs during the first four weeks after the onset of spring thaw.
Some states plan seasonal weight restrictions. For example, Pennsylvania schedules restrictions from February 15th to April 15th based on years of weather data. However, they reserve the authority to post additional restrictions due to unforeseen severe weather conditions.
The State of North Dakota has taken a much more different approach. They utilize temperature probes in the base layer sections, long range temperature forecasts, and sensors in the pavement to evaluate the strength of roadway bases to forecast when load restrictions should be imposed or removed.
A review of transportation departments indicates 16 states have implemented frost laws or seasonal load restrictions. In many states, seasonal weight restrictions are managed by local governments or jurisdictions. Most Canadian provinces also have established spring thaw speed and weight laws.
Note: The strength of a roadway is affected by moisture in the base materials supporting the roadway. The condition of road surface—moisture or frost on the roadway—does not affect roadway strength.
In general, during the spring thaw, maximum axle weights and gross vehicle weights will be reduced as much as 35%. Each state or province has established maximum axle and gross vehicle weights for key national and state trucking routes.
Because these spring load restrictions will vary so widely by state, and even within a state and because seasonal restrictions may be posted on short notice, it is best to check each state’s freeze/thaw laws prior to each trip. Links to seasonal restriction information for each US state or Canadian province are posted above.
Frost laws are created for the States and Providences in the USA and Canada that experience very low temperatures in the winter months frost laws may be enacted. These frost laws have been created to protect the State of Providences from highway and road damage caused by the surface cracking which is a direct result of too much weight being placed on the pavement which causes stress cracks thus damaging it. Also, when the freezing temperatures start to thaw out at times the water can not escape quickly which will cause the water to build up which can weaken the base structure of the road or highway which again causes damages the the pavement. Damages from thawing are just as severe if not even more extreme than frozen damages as they occur to the upper structure of the pavement rather than the base structure. In some areas during the winter months actual federal weight limits for the trucking industry (80,000 pounds gross) have been reduced with a reduction in driving speeds as well. This reduction has been observed as high as 35% in weight and even more in maximum speeds. Some States and Providences close winter and spring travel in certain areas.
It is very important that managers of trucking and transportation companies are aware of the open and closed months, days and times these particular laws are in effect as you can’t make an arrangement with a customer to ship their item if the state will not let you ship it due to frost or thaw laws being in effect. We are creating a contact list (EDIT ADD LINK) of each state that has frost laws enacted for the trucking industry for you to contact for further information.
It is important for you to check with the DOT, DMV, Port of entry or governing office of that particular area for clarification of the specific rules and regulations.