This is always my first sure sign that spring is on the way! Tonight at midnight the Minnesota Department of Transportation (MnDOT) will be putting on spring load restrictions in the south and southeast zones. March 15 is the day spring road restrictions go on every spring unless MnDOT determines the weather has been warm enough that they need to go on earlier. I believe most counties and townships follow the lead of MnDOT and put their load restrictions on at the same time.

MnDOT does not just guess when the spring load restrictions need to be put on. They have a number of sites where they monitor the frost depth under the roads in each zone. I am sure the frost goes deeper under a road than in a field because there is no snow to insulate the ground. When the frost begins to melt and reach a certain point MnDOT puts on the spring load restrictions. The weather determines when MnDOT  removes the restrictions.

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