Opinion of the Court. 234 U. S. policy of the Government is to be found in its statutes and when the law-making power speaks upon a particular subject over which it has constitutional power to legislate, public policy in such cases is what the statute enacts. Logan v. Postal Tel. Co., 157 Fed. Rep. 570, 587; United States v. Freight Association, 166 U. S. 340; Chi., B. & Q. R. R. Co. v. McGuire, 219 U. S. 549, 569. The subject has not been acted upon in any way by Congress or by the Interstate Commerce Commission, directly or indirectly. The act does not in any way conflict with any act of Congress or any rule or regulation of the Interstate Commerce Commission, and in the absence of such conflict the Federal courts will not declare the act invalid as interfering with interstate commerce. Savage v. Jones, 225 U. S. 501, 533; Mo. Pac. Ry. v. Larabee Mills, 211 U. S. 612, 623; Reid v. Colorado, 187 U. S. 137, 148. MR. JUSTICE HUGHES delivered the opinion of the court. The Atlantic Coast Line Railroad Company, the plaintiff in error, was convicted of violating a statute of the State of Georgia known as the 'headlight law.' Pub. Laws (Ga.), 1908, pp. 50, 51; Civil Code, §§ 2697, 2698. In defense it was insisted that the act contravened the commerce clause and the Fourteenth Amendment of the Constitution of the United States. On appeal from the judgment of conviction the Court of Appeals of the State of Georgia certified the questions thus raised, together with others involving the application of the state constitution, to the Supreme Court of the State. Answering these questions, that court sustained the validity of the statute (135 Georgia, 545), whereupon final judgment was entered and this writ of error was sued out. The material portions of the statute are as follows: "Section 1. Be it enacted by the General Assembly of Georgia, and it is hereby enacted by authority of the same, That all railroad companies are hereby required to equip and maintain each and every locomotive used by such company to run on its main line after dark with a good and sufficient headlight which shall consume not less than three hundred watts at the arc, and with a reflector not less than twenty-three inches in diameter, and to keep the same in good condition. The word main line as used herein means all portions of the railway line not used solely as yards, spurs and sidetracks. "Section 2. Be it further enacted, That any railroad company violating this Act in any respect shall be liable to indictment as for a misdemeanor in any county in which the locomotive not so equipped and maintained may run, and on conviction shall be punished by fine as prescribed in Section 1039 of the Code of 1895. "Section 4. Provided this Act shall not apply to tram roads, mill roads and roads engaged principally in lumber or logging transportation in connection with mills." The contention is made that this act deprives the company of its liberty of contract, and of its property, without due process of law. It compels the disuse of a material part of the company's present equipment and the substitution of a new appliance. The use of locomotive headlights, however, is directly related to safety in operation. It cannot be denied that the protective power of government, subject to which the carrier conducts its business and manages its property, extends as well to the regulation of this part of the carrier's equipment as to apparatus for heating cars or to automatic couplers. The legislature may require an adequate headlight, and whether the carrier's practise is properly conducive to safety, or a new method affording greater protection should be substituted, is a matter for the legislative judgment. But it is insisted that the legislature has gone beyond the Opinion of the Court. 234 U. S. limits of its authority in making the specific requirements contained in the act as to the character and power of the light and the dimensions of the reflector. This argument ignores the established principle that if its action is not arbitrary is reasonably related to a proper purpose― the legislature may select the means which it deems to be appropriate to the end to be achieved. It is not bound to content itself with general directions when it considers that more detailed measures are necessary to attain a legitimate object. Particularization has had many familiar illustrations in cases where there has been a conviction of the need of it, as, for example, in building regulations and in provisions for safeguarding persons in the use of dangerous machinery. So far as governmental power is concerned, we know of no ground for an exception in the case of a locomotive headlight: It cannot be said that the legislature acted arbitrarily in prescribing electric light, in preference to others, or that, having made this selection, it was not entitled to impose minimum requirements to be observed in the use of the light. Witnesses for the plaintiff in error, including its general superintendent of motive power and other employés holding important positions and conversant with the exigencies of operation, presented their objections to the use of the electric headlight. Locomotive engineers who for many years had driven locomotives with such a light testified for the State, expressing a decided opinion in favor of the use of electric headlights in the interest of safe operation and submitting their views in answer to the objections that had been urged. Assuming that there is room for differences of opinion, this fact does not preclude the exercise of the legislative discretion. So far as the question was one simply of expediency-as to the best method to provide the desired security-it was within the competency of the legislature to decide it. N. Y. & N. E. R. R. Co. v. Bristol, 151 U. S. 556, 571; C., B. & Q. Ry Co. v. Drainage Com'rs, 200 U. S. 561, 583, 584; McLean v. Arkansas, 211 U. S. 539, 547, 548; C., B. & Q. R. R. Co. v. McGuire, 219 U. S. 549, 568, 569, and cases there cited. As to the objection that the statute makes no provision for conditions beyond the carrier's control, it is sufficient to say that in the light of the construction placed upon the act by the Supreme Court of the State, we are not at liberty to regard it as open to this criticism (135 Georgia, pp. 561, 562); certainly, no such case is here presented. We conclude that there is no valid objection to the statute upon the ground that it deprives the carrier of liberty or property without due process of law. The further contention is that the statute offends in denying to the plaintiff in error the equal protection of the laws. Specifically, the complaint is that the act does not apply to receivers operating railroads, and that it expressly excepts tram roads, mill roads and roads engaged principally in lumber or logging transportation in connection with mills. As to the first, it cannot be said that the act does exclude receivers from its requirements. The state court has ruled that the words 'railroad company' in the statute include natural persons as well as corporations. It declined to decide that receivers were not included; but, conceding, without deciding, that they were not, it was held that the statute would not for that reason violate the equal protection clause in view of the temporary and special character of receivers' management. 135 Georgia, pp. 555, 556. We concur in this view. As to the exceptions made by the statute of tram roads, mill roads, etc., it is impossible to say that the differences with respect to operation and traffic conditions did not present a reasonable basis for classification. Lindsley v. Natural Carbonic Gas Co., 220 U. S. 61, 78, 81; Barrett v. Indiana, 229 U. S. 26, 30; German Alliance Ins. Co. v. Kansas, 233 U. S. 389, 418. VOL. CCXXXIV-19 Finally, it is urged that the statute constitutes an unwarrantable interference with interstate commerce. The locomotive, with respect to which the accusation was made, was at the time being regularly used in the hauling of interstate freight trains over the company's main line of railroad and was equipped with an oil headlight. The statute, as the Supreme Court of the State said, was not directed against interstate commerce, but it was held that it incidentally applied to locomotives used in hauling interstate trains while these were moving on the main line in the State of Georgia. This being so, the act is said to be repugnant to the exclusive power of Congress. It is argued that if Georgia may prescribe an electric headlight, other States through which the road runs may require headlights of a different sort; that, for example, some may demand the use of acetylene and that others may require oil; and that, if state requirements conflict, it will be necessary to carry additional apparatus and to make various adjustments at state lines which would delay and inconvenience interstate traffic. The argument is substantially the same as that which was strongly presented to the court in New York, New Haven & Hartford R. R. Co. v. New York, 165 U. S. 628, where the plaintiff in error was held subject to penalty for the violation of a New York statute which in substance made it unlawful for any steam railroad doing business in that State to heat its passenger cars, on any other than mixed trains, by any stove or furnace kept inside of the car or suspended therefrom. The railroad company was a Connecticut corporation having but a few miles of road within the State of New York and operating through trains from New York through Connecticut to Massachusetts. As this court said in its opinion, the argument was made that 'a conflict between state regulations in respect of the heating of passenger cars used in interstate commerce would make safe and rapid |