In the matter of motor vehicle taxation, on the other hand, durable and consistent results have been achieved. This is because most such taxation has been readily classifiable as the exaction of a toll for the use of the State's highways, and the only question was whether the toll was exorbitant. Moreover, such taxation is apt to be designed not merely to raise revenue but to promote safety on the highways. In the leading case, Hendrick _v._ Maryland,[738] decided in 1915, the Court took cognizance of the fact that "the movement of motor vehicles over the highways is attended by constant and serious dangers to the public, and is also abnormally destructive to the ways themselves";[739] and on this factual basis it has held that registration may be required by a State for out-of-State vehicles operated therein,[740] or passing through from one State to another;[741] that a special fee may be exacted for the privilege of transporting motor vehicles on their own wheels in caravans,[742] unless excessive;[743] that taxes may also be imposed on carriers based on capacity[744] or mileage,[745] or as a flat fee;[746] but that a privilege tax on motor busses operated exclusively in interstate commerce, cannot be sustained unless it appears affirmatively in some way, that it is levied only as compensation for use of the highways in the State or to defray the expense of regulating motor traffic.[747] Later decisions follow in the same general track,[748] the most recent one being Capitol Greyhound Lines _v._ Brice,[749] in which the Court, speaking by Justice Black passed upon a Maryland excise tax on the fair market value of motor vehicles used in interstate commerce as a condition to the issuance of certificates of title as prerequisites to the registration and operation of motor vehicles in the State. Because the tax was applied to vehicles used in both interstate and intrastate commerce and the proceeds were used for road purposes and because the Court considered the tax, though actually separate, to be an adjunct of Maryland's mileage tax, it was able to find that the total charge varied substantially with the mileage travelled, and on that ground sustained it, being constant, it said with "rough approximation rather than precision," no showing having been made that Maryland's taxes considered as a whole exceeded "fair compensation for the privilege of using State roads." Justice Frankfurter, who was joined by Justice Jackson, dissented, and in so doing contributed as an Appendix to his opinion a useful analysis of decisions involving State taxation of motor vehicles engaged in interstate commerce, for highway purposes.[750] Public Utilities; Regulatory Charges