The Commissioner, upon written application made by the owner or operator, shall issue overweight permits for operation of certain vehicles used to haul concrete. Permits under this section shall be issued only for vehicles that are used exclusively for the mixing of concrete in transit or at a project site or for transporting necessary components in a compartmentalized vehicle to produce concrete immediately upon arrival at a project site and either have (i) four axles with more than 22 feet between the first and last axle of the vehicle or (ii) three axles. Any vehicle operating under a permit issued pursuant to this section shall have a gross weight of no more than 60,000 pounds for three-axle vehicles and 70,000 pounds for four-axle vehicles, a single axle weight of no more than 20,000 pounds, tandem axle weight of no more than 40,000 pounds, and a tri-axle grouping weight of no more than 50,000 pounds, with no single axle of such tri-axle grouping exceeding the weight permitted for a single axle. The fee for such permits shall be as provided in § 46.2-1140.1. Such permit shall not designate the route to be traversed nor contain restrictions or conditions not applicable to other vehicles in their general use of the highways. Each vehicle, when loaded according to the provisions of a permit issued under this section, shall be operated at a reduced speed. The reduced speed limit is to be 10 miles per hour slower than the legal speed limit in 55, 45, and 35 miles per hour speed limit zones.