You’re not imagining it: Mud season has arrived and it’s early, maybe the earliest ever.

On Friday the state began posting weight limits on roads to keep heavy vehicles from damaging pavement as it thaws and buckles. The N.H. Department of Transportation makes this announcement every year but since 2005, when records became available, it has never been made this early in the season.

Only three previous times in the 16 years for which records exist has the announcement been made in late February rather than in March. The closest to this year’s date was in 2018 when the state road posting announcement came on Feb. 21, but usually it is made in the first or second week of March. In 2005, a late winter meant the announcement wasn’t made until March 31.

Alan Hanscom, state maintenance engineer for the DOT, said the state has “done some brief periods in January at times, but it did get colder and the signs came back down.” It takes an uninterrupted period of below-freezing temperatures to make highways become “solidly frozen” again, as required by regulations, and with Concord daytime temperatures slated to be in the 40s or 50s in the coming week and the March forecast calling for average temperatures, that seems unlikely to happen this year.

An early mud season is, like canceled outdoor winter sporting events and shortage of snow cover, the latest effect of this unseasonably warm winter.

Except for the brutally cold weekend of Feb. 3-5, temperatures have consistently been at or above long-term averages throughout New England since before Christmas. Seven Northeast states had the warmest January on record.

Warmer weather means sections of roads are vulnerable to breaking up as frost melts from under the road base.

Water, almost uniquely among all compounds, expands rather than shrinks when it freezes. When temperatures in late winter or early spring vacillate between freezing and thawing, water that has seeped underneath roads grows in the cold, pushing up pavement, then shrinks when it’s warm, leaving gaps where more liquid water can enter.

As this process repeats itself the road becomes weaker and more likely to break up when vehicles drive over it. Heavier vehicle are more likely to cause the damage; hence the need for weight limits at this time of year.

Weight limits can also limit damage to unpaved roads, surfaced with loose gravel or dirt.

Road postings are determined by local DOT district engineers. Many cities and towns make similar postings on their own roads as determined by their own road crews.

The maximum allowable vehicular weight posted sections of state highways is 30,000 pounds gross weight or the cumulative width in inches of all tires contacting the road surface multiplied by 300, whichever is less.

Under state law (Section 236:3-a), trucks carrying home heating oil, processed milk products or maple sap and septic pumper trucks are exempted from seasonal bans, as long as they get the approval of local district engineers.

Affected roads can be found on the Web at newengland511.org/under the top banner “Trucking-New Hampshire-Seasonal Posting.”

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