In the exercise of power to prescribe just and reasonable rates and charges for the transportation of property by common carriers by motor vehicle, and classifications, regulations, and practices relating thereto, and to disallow rates filed by any carriers, the administrator shall give due consideration, among other factors, to the inherent advantages of transportation by the carriers; to the effect of rates upon the movement of traffic by the carrier or carriers for which the rates are prescribed; to the need, in the public interest, of adequate and efficient transportation service of the carriers at the lowest cost consistent with the furnishing of the service; and to the need of revenues sufficient to enable the carriers under honest, economical, and efficient management to provide such service. In any proceeding to determine the justness and reasonableness of any rates or charges of any common carrier, there shall not be taken into consideration or allowed, as evidence or elements of value of the property of the carrier, either good will, earning power, or the certificate under which the carrier is operating. At any hearing involving a change in rates, charges, or classification, or in a rule, regulation, or practice, the burden of proof shall be upon the carrier to show that the proposed rule, changed rate, charge, classification, regulation, or practice is just and reasonable.