(1) Motor carriers are divided into three classes to be known as: (a) Class A motor carriers; (b) Class D motor carriers; and (c) Class E motor carriers. (2) Class A motor carriers include all motor carriers operating between fixed termini or over a regular route and under regular rates or charges, based upon either station-to-station rates or upon a mileage rate or scale. (3) Class D motor carriers include all motor carriers operating motor vehicles transporting garbage. (4) Class E motor carriers include all transportation network carriers.