The owner of any motor vehicle used for hauling Virginia-grown forest or farm products, as defined in § 3.2-4709, from the place where they are first produced, cut, harvested, or felled to the location where they are first processed may obtain from the Commissioner an extension for such vehicle of the single axle, tandem axle, and gross weight limits set forth in this title. The permit shall extend the single axle, tandem axle, and gross weight limits set forth in this title. The permit shall extend the single axle, tandem axle, and gross weight limits based on axle spacing and number of axles on such vehicle by five percent, respectively. However, no such permit shall authorize the operation of a motor vehicle whose gross weight exceeds 84,000 pounds. No permit issued under this section shall permit the operation on an interstate highway of any vehicle with (i) a single axle weight in excess of 20,000 pounds, or (ii) a tandem axle weight in excess of 34,000 pounds, or (iii) a gross weight, based on axle spacing, greater than that permitted in § 46.2-1126, or (iv) a gross weight, regardless of axle spacing, in excess of 80,000 pounds. The Commissioner may promulgate regulations governing such permits. Weight extensions provided in this section shall be in addition to those provided in § 46.2-1128, but no weights beyond those permitted by the combination of the extensions provided in this section and § 46.2-1128 shall be tolerated. Vehicles that are registered as farm use vehicles as provided in § 46.2-698 may operate as authorized under this section; provided, however, that should such vehicle violate the weight limits permitted by this section and § 46.2-1128, such vehicle shall no longer be permitted to operate as authorized in this section.