Mr. Justice Stewart
delivered the opinion of the Court.
This appeal from a judgment of the Supreme Court of Michigan draws in question the constitutional validity of certain provisions of Detroit’s Smoke Abatement Code as applied to ships owned by the appellant and operated in interstate commerce.
The appellant is a Michigan corporation, engaged in the manufacture and sale of cement. It maintains a fleet of five vessels which it uses to transport cement from its mill in Alpena, Michigan, to distributing plants located in various states bordering the Great Lakes. Two of the ships, the S. S. Crapo and the S. S. Boardman, are equipped with hand-fired Scotch marine boilers. While these vessels are docked for loading and unloading it is necessary, in order to operate deck machinery, to keep the boilers fired and to clean the fires periodically. When the fires are cleaned, the ship’s boiler stacks emit smoke which in density and duration exceeds the maximum standards allowable under the Detroit Smoke Abatement Code. Structural alterations would be required in order to insure compliance with the Code.
Criminal proceedings were instituted in the Detroit Recorder’s Court against the appellant and its agents for violations of the city law during periods when the vessels were docked at the Port of Detroit. The appellant brought an action in the State Circuit Court to enjoin the city from further prosecuting the pending litigation in the Recorder’s Court, and from otherwise enforcing the smoke ordinance against its vessels, “except where the emission of smoke is caused by the improper firing or the improper use of the equipment upon said vessels.” The Circuit Court refused to grant relief, and the Supreme Court of Michigan affirmed, 355 Mich. 227, 93 N. W. 2d 888. An appeal was lodged here, and we noted probable jurisdiction, 361 U. S. 806.
In support of the claim that the ordinance cannot constitutionally be applied to appellant’s ships, two basic arguments are advanced. First, it is asserted that since the vessels and their equipment, including their boilers, have been inspected, approved and licensed to operate in interstate commerce in accordance with a comprehensive system of regulation enacted by Congress, the City of Detroit may not legislate in such a way as, in effect, to impose additional or inconsistent standards. Secondly, the argument is made that even if Congress has not expressly pre-empted the field, the municipal ordinance “materially affects interstate commerce in matters where uniformity is necessary.” We have concluded that neither of these contentions can prevail, and that the Federal Constitution does not prohibit application to the appellant's vessels of the criminal provisions of the Detroit ordinance.
The ordinance was enacted for the manifest purpose of promoting the health and welfare of the city’s inhabitants. Legislation designed to free from pollution the very air that people breathe clearly falls within the exercise of even the most traditional concept of what is com-pendiously known as the police power. In the exercise of that power, the states and their instrumentalities may act, in many areas of interstate commerce and maritime activities, concurrently with the federal government. Gibbons v. Ogden, 9 Wheat. 1; Cooley v. Board of Wardens of Port of Philadelphia, 12 How. 299; The Steamboat New York v. Rea, 18 How. 223; Morgan v. Louisiana, 118 U. S. 455; The Minnesota Rate Cases, 230 U. S. 352; Wilmington Transp. Co. v. California Railroad Comm., 236 U. S. 151; Vandalia R. Co. v. Public Service Comm., 242 U. S. 255; Stewart & Co. v. Rivara, 274 U. S. 614; Welch Co. v. New Hampshire, 306 U. S. 79.
The basic limitations upon local legislative power in this area are clear enough. The controlling principles have been reiterated over the years in a host of this Court’s decisions. Evenhanded local regulation to effectuate a legitimate local public interest is valid unless preempted by federal action, Erie R. Co. v. New York, 233 U. S. 671; Oregon-Washington Co. v. Washington, 270 U. S. 87; Napier v. Atlantic Coast Line, 272 U. S. 605; Missouri Pacific Co. v. Porter, 273 U. S. 341; Service Transfer Co. v. Virginia, 359 U. S. 171, or unduly burdensome on maritime activities or interstate commerce, Minnesota v. Barber, 136 U. S. 313; Morgan v. Virginia, 328 U. S. 373; Bibb v. Navajo Freight Lines, 359 U. S. 520.
In determining whether state regulation has been preempted by federal action, “the intent to supersede the exercise by the State of its police power as to matters not covered by the Federal legislation is not to be inferred from the mere fact that Congress has seen fit to circumscribe its regulation and to occupy a limited field. In other words, such intent is not to be implied unless the act of Congress fairly interpreted is in actual conflict with the law of the State.” Savage v. Jones, 225 U. S. 501, 533. See also Reid v. Colorado, 187 U. S. 137; Asbell v. Kansas, 209 U. S. 251; Welch Co. v. New Hampshire, 306 U. S. 79; Maurer v. Hamilton, 309 U. S. 598.
In determining whether the state has imposed an undue burden on interstate commerce, it must be borne in mind that the Constitution when “conferring upon Congress the regulation of commerce, . . . never intended to cut the States off from legislating on all subjects relating to the health, life, and safety of their citizens, though the legislation might indirectly affect the commerce of the country. Legislation, in a great variety of ways, may affect commerce and persons engaged in it without constituting a regulation of it, within the meaning of the Constitution.” Sherlock v. Alling, 93 U. S. 99, 103; Austin v. Tennessee, 179 U. S. 343; Louisville & Nashville R. Co. v. Kentucky, 183 U. S. 503; The Minnesota Rate Cases, 230 U. S. 352; Boston & Maine R. Co. v. Armburg, 285 U. S. 234; Collins v. American Buslines, Inc., 350 U. S. 528. But a state may not impose a burden which materially affects interstate commerce in an area where uniformity of regulation is necessary. Hall v. DeCuir, 95 U. S. 485; Southern Pacific Co. v. Arizona, 325 U. S. 761; Bibb v. Navajo Freight Lines, 359 U. S. 520.
Although verbal generalizations do not of their own motion decide concrete cases, it is nevertheless within the framework of these basic principles that the issues in the present case must be determined.
I.
For many years Congress has maintained an extensive and comprehensive set of controls over ships and shipping. Federal inspection of steam vessels was first required in 1838, 5 Stat. 304, and the requirement has been continued ever since. 5 Stat. 626; 10 Stat. 61; 14 Stat. 227; 16 Stat. 440; 22 Stat. 346; 28 Stat. 699; 32 Stat. 34; 34 Stat. 68; 60 Stat. 1097; 73 Stat. 475. Steam vessels which carry passengers must pass inspection annually, 46 U. S. C. § 391 (a), and those which do not, every two years. 46 U. S. C. §391 (b). Failure to meet the standards invoked by law results in revocation of the inspection certificate, or refusal to issue a new one, 46 U. S. C. § 391(d). It is unlawful for a vessel to operate without such a certificate. 46 U. S. C. § 390c (a).
These inspections are broad in nature, covering “the boilers, unfired pressure vessels, and appurtenances thereof, also the propelling and auxiliary machinery, electrical apparatus and equipment, of all vessels subject to inspection . . . .” 46 U. S. C. § 392 (b). The law provides that “No boiler . . . shall be allowed to be used if constructed in whole or in part of defective material or which because of its form, design, workmanship, age, use, or for any other reason is unsafe.” 46 U. S. C. § 392 (c).
As is apparent on the face of the legislation, however, the purpose of the federal inspection statutes is to insure the seagoing safety of vessels subject to inspection. Thus 46 U. S. C. § 392 (c) makes clear that inspection of boilers and related equipment is for the purpose of seeing to it that the equipment “may be safely employed in the service proposed.” The safety of passengers, 46 U. S. C. § 391 (a), and of the crew, 46 U. S. C. § 391 (b), is the criterion. The thrust of the federal inspection laws is clearly limited to affording protection from the perils of maritime navigation. Cf. Ace Waterways v. Fleming, 98 F. Supp. 666. See also Steamship Co. v. Joliffe, 2 Wall. 450.
By contrast, the sole aim of the Detroit ordinance is the elimination of air pollution to protect the health and enhance the cleanliness of the local community. Congress recently recognized the importance and legitimacy of such a purpose, when in 1955 it provided:
“[I]n recognition of the dangers to the public health and welfare, injury to agricultural crops and livestock, damage to and deterioration of property, and hazards to air and ground transportation, from air pollution, it is hereby declared to be the policy of Congress to preserve and protect the primary responsibilities and rights of the States and local governments in controlling air pollution, to support and aid technical research to devise and develop methods of abating such pollution, and to provide Federal technical services and financial aid to State and local government air pollution control agencies and other public or private agencies and institutions in the formulation and execution of their air pollution abatement research programs.” 69 Stat. 322; 42 U. S. C. § 1857.
Congressional recognition that the problem of air pollution is peculiarly a matter of state and local concern is manifest in this legislation. Such recognition is underlined in the Senate Committee Report:
“The committee recognizes that it is the primary responsibility of State and local governments to prevent air pollution. The bill does not propose any exercise of police power by the Federal Government and no provision in it invades the sovereignty of States, counties or cities.” S. Rep. No. 389, 84th Cong., 1st Sess. 3.
We conclude that there is no overlap between the scope of the federal ship inspection laws and that of the municipal ordinance here involved. For this reason we cannot find that the federal inspection legislation has pre-empted local action. To hold otherwise would be to ignore the teaching of this Court’s decisions which enjoin seeking out conflicts between state and federal regulation where none clearly exists. Savage v. Jones, 225 U. S. 501; Welch Co. v. New Hampshire, 306 U. S. 79; Maurer v. Hamilton, 309 U. S. 598.
An additional argument is advanced, however, based not upon the mere existence of the federal inspection standards, but upon the fact that the appellant’s vessels were actually licensed, 46 U. S. C. § 263, and enrolled, 46 U. S. C. §§ 259-260, by the national government. It is asserted that the vessels have thus been given a dominant federal right to the use of the navigable waters of the United States, free from the local impediment that would be imposed by the Detroit ordinance.
The scope of the privilege granted by the federal licensing scheme has been well delineated. A state may not exclude from its waters a ship operating under a federal license. Gibbons v. Ogden, 9 Wheat. 1. A state may not require a local occupation license, in addition to that federally granted, as a condition precedent to the use of its waters. Moran v. New Orleans, 112 U. S. 69. While an enrolled and licensed vessel may be required to share the costs of benefits it enjoys, Huse v. Glover, 119 U. S. 543, and to pay fair taxes imposed by its domicile, Transportation Co. v. Wheeling, 99 U. S. 273, it cannot be subjected to local license imposts exacted for the use of a navigable waterway, Harman v. Chicago, 147 U. S. 396. See also Sinnot v. Davenport, 22 How. 227.
The mere possession of a federal license, however, does not immunize a ship from the operation of the normal incidents of local police power, not constituting a direct regulation of commerce. Thus, a federally licensed vessel is not, as such, exempt from local pilotage laws, Cooley v. Board of Wardens of Port of Philadelphia, 12 How. 299, or local quarantine laws, Morgan's Steamship Co. v. Louisiana Board of Health, 118 U. S. 455, or local safety inspections, Kelly v. Washington, 302 U. S. 1, or the local regulation of wharves and docks, Packet Co. v. Catlettsburg, 105 U. S. 559. Indeed this Court has gone so far as to hold that a state, in the exercise of its police power, may actually seize and pronounce the forfeiture of a vessel “licensed for the coasting trade, under the laws of the United States, while engaged in that trade.” Smith v. Maryland, 18 How. 71, 74. The present case obviously does not even approach such an extreme, for the Detroit ordinance requires no more than compliance with an orderly and reasonable scheme of community regulation. The ordinance- does not exclude a licensed vessel from the Port of Detroit, nor does it destroy the right of free passage. We cannot hold that the local regulation so burdens the federal license as to be constitutionally invalid.
II.
The claim that the Detroit ordinance, quite apart from the effect of federal legislation, imposes as to the appellant’s ships an undue burden on interstate commerce needs no extended discussion. State regulation, based on the police power, which does not discriminate against interstate commerce or operate to disrupt its required uniformity, may constitutionally stand. Hennington v. Georgia, 163 U. S. 299; Lake Shore & Mich. South. R. Co. v. Ohio, 173 U. S. 285; Pennsylvania Gas Co. v. Public Service Comm., 252 U. S. 23; Milk Board v. Eisenberg Co., 306 U. S. 346; Bob-Lo Excursion Co. v. Michigan, 333 U. S. 28.
It has not been suggested that the local ordinance, applicable alike to “any person, firm or corporation” within the city, discriminates against interstate commerce as such. It is a regulation of general application, designed to better the health and welfare of the community. And while the appellant argues that other local governments might impose differing requirements as to air pollution, it has pointed to none. The record contains nothing to suggest the existence of any such competing or conflicting local regulations. Cf. Bibb v. Navajo Freight Lines, 359 U. S. 520. We conclude that no impermissible burden on commerce has been shown.
The judgment is affirmed.
The Detroit legislation also contains provisions making it unlawful to operate any combustion equipment in the city without a certificate, § 2.16, providing for an annual inspection of all such equipment used in the city, § 2.17, and further providing for the sealing of equipment in the event that the inspection requirements are repeatedly ignored, § 2.20. There is nothing in the record to indicate that the city has at any time attempted to enforce these provisions with respect to the appellant’s ships. Accordingly, we do not reach the question of the validity of the inspection sections as they might be applied to appellant, but limit our consideration solely to what is presented upon this record — the enforcement of the criminal provisions of the Code for violation of the smoke emission provisions.
Compare, Napier v. Atlantic Coast Line R. Co., where the Court concluded that “the [Locomotive] Boiler Inspection Act . . . was intended to occupy the field.” 272 U. S. 605, 613.