Aug 23, 2022 2 min read

OS/OW Thaw OPS or Frost Laws

Thaw season represents the temporary restrictions on the weight and speed limits of traffic on susceptible-to-thaw roadways. Always check the DOT's website or the appropriate resources for the most up-to-date information.

Numerous states appear to be purposefully vague regarding actual weight restrictions, preferring case-by-case determinations and limitations. Obtaining information may require contacting the state's highway department. The requirements are determined based on actual temperature, soil moisture content, and observed road conditions. Take note that different weight restrictions may apply in different parts of the state.

Today, science is more advanced in its application of "Frost Laws," also known as "Seasonal Weight Restrictions," which have demonstrated that a functional balance can be struck between preserving critical highway infrastructure and optimizing trucking operations.

Many US States enact laws that restrict vehicle loads during spring months, in climates that experience below-freezing temperatures and damage to roads from thaw-weakening.

Over the last decade, road construction technology has advanced. The most noticeable winter damage is the formation of potholes, which are caused by moisture in the pavement freezing and weakening the road's top layer. Modern road construction materials significantly reduce the amount of moisture retained in the top layers, thereby decreasing the likelihood of potholes. The base and subbase, on the other hand, are still subject to varying amounts of moisture, which are influenced by spring rain and melt water.

Thaw is defined by trapped moisture beneath the pavement that softens the roadbed and weakens the road's supporting structure. As excess moisture evaporates or drains away, the road bed stabilizes and reverts to its original design strength.

Due to the seasonal variation in temperatures, states and provinces must manage weight and speed restrictions seasonally to protect and preserve roads while ensuring maximum access for trucking interests.

Fun fact: 16 DOT’s have seasonal load regulation.

Overall, maximum axle weights and gross vehicle weights may be reduced by up to 35% during the spring thaw. Each state or province has established axle and gross vehicle weight limits for critical interstate and intrastate trucking routes.

Spring load restrictions vary significantly by state, and even within a state, and because seasonal restrictions may be posted at any given time, it is prudent to check required state's laws and freeze-thaw postings prior to each trip.