If the encroachment is not removed, or its removal not commenced and diligently prosecuted, prior to the expiration of 10 days from and after the service or posting of the notice, the person causing, owning, or controlling the encroachment forfeits three hundred fifty dollars ($350) for each day the encroachment continues unremoved. The road commissioner shall immediately remove an encroachment that effectually obstructs and prevents the use of the highway by vehicles.