regulations requiring motor carriers to provide adequate insurance protection for injuries caused by the negligent operation of their vehicles.[834] INVALID STATE ACTS AFFECTING MOTOR CARRIERS A State law which imposes upon all persons engaged in transporting for hire by motor vehicle over the public highways of the State the burdens and duties of common carriers and requires them to furnish bonds to secure the payment of claims and liabilities resulting from injury to property carried, may not be validly applied to a private carrier which is engaged exclusively in hauling from one State to another State the goods of particular factories under standing contracts with their owners, the said carrier enjoying neither a special franchise nor using the eminent domain power.[835] On the other hand, a State statute which prohibits common carriers for hire from using the highways of the State between fixed termini or over regular routes without having first obtained from a director of public works a certificate of public convenience, is primarily not a regulation to secure safety on the highways or to conserve them, but a ban on competition and, as applied to a common carrier by motor vehicle of passengers and express purely in interstate commerce, is both violation of the Commerce Clause and defeats the express purpose of Congressional legislation rendering federal aid for the construction of interstate highways.[836] TRANSPORTATION AGENCIES The special characteristics of motor travel have brought about a reversal of the Court's attitude toward State control of transportation agencies. Sustaining in 1941 a California statute requiring that agents engaged in negotiating for the transportation of passengers in motor vehicles over the highways of the State take out a license, Justice (later Chief Justice) Stone, speaking for the Court, said: "In Di Santo _v._ Pennsylvania,[837] this Court took a different view * * *, it held that a Pennsylvania statute requiring others than railroad or steamship companies, who engage in the intrastate sale of steamship tickets or of orders for transportation to and from foreign countries, to procure a license by giving proof of good moral character and filing a bond as security against fraud and misrepresentation to purchasers, was an infringement of the Commerce Clause. Since the decision in that case this Court has been repeatedly called upon to examine the constitutionality of numerous local regulations affecting interstate motor vehicle traffic. It has uniformly held that in the absence of pertinent Congressional legislation there is constitutional power in the States to regulate interstate commerce by motor vehicle wherever it affects the safety of the public or the safety and convenient use of its highways, provided only that the regulation does not in any other respect unnecessarily obstruct interstate commerce."[838] NAVIGATION; GENERAL DOCTRINE