Load restrictions are put in place to reduce damage to roadways caused by heavy loads at a time of year when highway pavements are most vulnerable. As the frost is leaving the ground during the spring thaw every year, the gravel under the roadbed has high moisture content, which weakens the load carrying capacity of the bituminous (asphalt concrete) road. "Therefore, in order to protect and prolong the service life of the roadways, axle weight restrictions are imposed during the spring thaw every year, when the roadbeds are most susceptible to damage (due to the weakened subgrade)," notes the Minnesota Department of Transportation (MnDOT).
Wisconsin Department of Transportation (WisDOT) notes on their website, "During this time when some pavements and base materials are at their weakest due to the freezing and thawing cycle occurring, most divisible load multiple trip permits exceeding legal axle weights or 80,000 pounds are suspended. (Divisible load permits authorized by Wis. Stat. ss. 348.27(9m)(a)4. and 348.27(9t) may operate during spring thaw subject to terms of each permit.) During the thaw period, overweight non-divisible multiple trip and single trip permits must stay off highway sections designated as Class II."
South Dakota Department of Transportation (SDDOT) notes on their website, "It is the Department's position to not implement Spring Load Restrictions any earlier than necessary. The Department monitors the daily high/low temperatures at numerous locations throughout the state. The high/low temperatures are used to calculate accumulated freeze and thaw indexes. Please be aware that this method is only one decision tool the Department uses to determine when to implement and remove load restrictions. The Department still relies heavily on the existing highway conditions and past experience of its field personnel when making the final decision of when to implement and remove load restrictions."
Spring load restrictions for counties in Minnesota are based on the Central Frost Zone starting and ending dates determined by MnDot. According to state statute, the weight on any single axle shall not exceed 5 tons on any unpaved street or highway; 10 tons on a paved street or highway unless posted otherwise between the dates set by the transportation commissioner. There are exceptions to spring load restrictions on the interstate according to MnDOT:
--- 10-ton limit does not apply to interstates (axle group or GVW). That is, full summer weight is allowed.
--- Interstate travel must be through movement only (no starting or stopping off the interstate system).
--- All other state highways are 10-ton, unless posted for less.
Many states/counties may grant other exemptions, so be sure to check all statutes. Some roadway sections are too weak to withstand even the legal load limit (80,000 pounds) during the seasonal freezing and thawing period. These highway sections have signs posted, indicating the allowable weight limits during the period normally from the second week in March until late April or early May, according to WisDOT.
While many farmers are still harvesting their 2019 corn, soybean and sunflower crops, especially in North Dakota, there are no "harvest" permits allowed during the spring load restriction period. North Dakota has a combination harvest/winter (durational) 10% weight exemption permit, which is valid from July 15 through March 7. During harvest season, July 15 through Nov. 30, applicable permit rules apply and during the winter season, Dec. 1 through March 7, or sooner if spring weight limits go into effect.
North Dakota permit rules state, "Overweight permits will not be issued during the period of spring road restrictions and on highways with road restrictions other than during the spring thaw, except as provided for in the Road Restriction Permit Policy (Policy 9-17) or unless an emergency has been declared." https://www.nd.gov/…
Every state provides information about when spring load restrictions begin, along with specific road postings. Here are links to some of the Upper Midwest DOTs:
Information on the MnDOT Seasonal Load limits can be found here: http://dotapp7.dot.state.mn.us/…
Information on the NDDOT Seasonal Load limits can be found here: https://www.dot.nd.gov/…
Information on the WisDOT Seasonal Load limits can be found here: https://wisconsindot.gov/…
Information on the SDDOT Seasonal Load limits can be found here: https://dot.sd.gov/…
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