Opinion by
Mr. Justice Roberts,With the advent of mechanical devices for controlling the movement of more than one train on a single track, many railroads in Pennsylvania have abandoned the old system of flagging, whereby a man was dispatched to the rear of a halted train to place flares and wave flags, thus insuring against rear end collisions. The abandoning of the flaggers forms the basis of this controversy.
On July 22, 1964, a union filed a complaint before the Pennsylvania Public Utility Commission against the Pittsburgh and Lake Erie R. R. Co., alleging that the railroad had amended its rule 99 to eliminate flagging in those areas controlled by automatic signal devices, that this amendment has resulted in an unsafe warning procedure, and that the interests of public safety required that the commission order the railroad to reinstate its flagging controls. In October of the same year, the same union filed a “petition” against all railroads operating in Pennsylvania, including the P. & L. E., alleging that other railroads have also *342eliminated flagging, and urging the Commission to promulgate a rule to require flagging in all areas where a train stops under circumstances in which it may be. overtaken by another train. As a result of these two actions, the commission heard extensive testimony by experts from both the union and the railroads, and, as a result of this testimony, issued its Rule 16 on November 22, 1965, requiring flagging in all areas, subject to certain exceptions dealing with passenger train stops, interlocking plants, storage yards, and those semi-automatic signal systems in which oncoming trains are required to come to a complete stop. The railroads immediately took an appeal to the Superior Court.
Before argument could be heard, the union and the commission successfully petitioned the Superior Court to remand the case for further hearing on the ground that many of the Rule 16 exceptions were unclear. As a result of this remand, a new, amended version of Rule 16 was issued on December 19, 1966; this new rule contains no specific exceptions to the flagging requirements. In an opinion by President Judge Ervin, the Superior Court affirmed the commission’s order. 210 Pa. Superior Ct. 7, 232 A. 2d 220 (1967), and wo granted allocatur, limiting argument, however, to the issue of whether §25 of the Interstate Commerce Act, 49 U.S.C. §26,1 has preempted state regulation dealing *343with flag protection. Having thoroughly reviewed the applicable statutes and judicial precedents, we hold that federal legislation has preempted any state intervention in this particular area, a holding supported by three separate reasons.
First, there can be no doubt whatsoever that the mechanical devices specifically required by §25 per*344form the exact same function that manual flagging is intended to perform (i.e., increasing safety by preventing rear end collisions); second, the language used in §25 is broad enough to indicate that Congress has chosen to regulate the entire field of rear end collision prevention; and third, the Supreme Court of the United States has announced the rule that where federal language is broad enough to indicate preemption, a state law cannot escape interdiction on the ground that it does not conflict with the federal regulations actually passed.
The first reason for our decision today, that §25 devices perform the same function as flagging, needs’ little expansion. What is most significant about this identity of functions, however, is this. If one looks behind the actual mechanical devices themselves, §25 is really nothing more than a federal statute designed to keep one train from running into the rear of another. Congress having once determined how best to avoid this type of disaster, it is no longer open to the states to decide that the federal protections are inadequate, and that additional safety measures must be taken by interstate railroads whenever their trains run through Pennsylvania.
Furthermore, the language of §25 indicates that the Interstate Commerce Commission (now the Department of Transportation [D.O.T.] )2 has the power to require flag protection to supplement the safety features of mechanical collision prevention devices. In addition to requiring those types of automatic devices set out in the opening sentence of §25 (b), the Commission may also require “other similar appliances, methods, and systems intended to promote the safety of railroad op*345eration. . . .” The argument advanced by appellees that the §25 language is limited only to mechanical devices, whereas flagging cannot be classified as a device) at all, falls flat in the face of this language. For the statute, in addition to permitting the Commission to require “appliances” not specified in the statute itself, also permits the establishment of additional “methods and systems” to prevent rear end collisions. Flagging can certainly be classified as either a “method” or a “system.”
Admittedly, neither the ICC nor the DOT has ever issued any blanket regulations pursuant to §25 covering flag protection. However, not only is the federal agency’s failure to regulate flagging itself not dis-positive when the issue of preemption is raised, see cases cited and discussed infra, but furthermore, the ICC, in 1947, did issue an order requiring railroads under certain specified circumstances to supplement their automatic controls with flag protection. See Order No. 29543, issued pursuant to Appliances, Methods, and Systems Intended To Promote Safety of Railroad Operation, 268 I.C.C. 547, 560-61 (1947).3
*346It is certainly too late in the development of constitutional law to say that Congress may not preempt an entire field by the passage of a broad based statute, even though the regulations passed pursuant to that statute do not in fact cover every possible situation. Moreover, once such a statute is passed, and the intention to preempt state law in the area becomes manifest, the various states may not pass legislation even supplemental to the federal rules, so long as the area affected by these supplemental acts coincides with the federal bailiwick. For example, in Napier v. Atlantic Coast Line R.R. Co., 272 U.S. 605, 47 S. Ct. 207 (1926), two state statutes which required automatic fire doors and cab curtains on locomotives were declared unconstitutional on the ground that the federal Locomotive Boiler Inspection Act was the exclusive pronouncement on mandatory locomotive equipment. No one in Napier contended that the federal act actually had any provisions relating to such cab curtains and fire doors. The Supreme Court nevertheless held that the states were powerless to supplement the federal equipment requirements with additional safeguards of their own. The appellee in the present case attempts to distinguish Napier by relying on In Re Complaint of Brotherhood of R.R. Trainmen v. Public Utility Commissioners of New Jersey, 49 N.J. 174, 229 A. 2d 505 (1967). However, in our view, New Jersey’s explanation of Napier is unsatisfactory.
According to the Brotherhood decision, Napier does not control because it dealt with equipment actually attached to the locomotive and passing from state to *347state, rather than with a requirement styled by the New* Jersey Court as a “supplemental local emergency safety device.” We believe this to be a distinction without legal substance. Just as in the present case, an attempt was made in Napier to show that the state law was aimed at a completely different evil than that covered by the Boiler Inspection Act. It was there contended that the federal locomotive requirements were intended to keep trains from having accidents, whereas the local fire door and cab curtain statutes were designed for engineer health and safety. That argument failed to persuade the Supreme Court of the United States. So also is this Court unmoved by an argument based on the purely “supplemental” nature of flagging. In fact, it would seem that Napier is a much weaker case for a finding of federal preemption than this insofar as the state statute there was intended to remedy a different problem than the federal law, whereas in the present case, the appellee’s best argument is that flagging “supplements” automatic devices.
Finally, on this issue of supplemental state legislation, we shall follow the case of Pennsylvania R. Co. v. Public Service Commission of Pennsylvania, 250 U.S. 566, 40 S. Ct. 36 (1919). Pennsylvania had enacted a statute requiring cabooses to be equipped with rear platforms of certain minimum dimensions, even though the applicable federal statute permitted cabooses with no such platforms. In answer to the argument that the Pennsylvania statute merely “supplemented” the federal law by making cabooses safer, Mr. Justice Holmes had only to say: “when the United States has exercised its exclusive powers over interstate commerce as far as to take possession of the field, the States no more can supplement its requirements than they can annul them.” 250 U.S. at 569, 40 S. Ct. at 37.
*348Agreeing with this great Justice, and believing that his words are just as applicable to the present case, we reverse the orders of the Superior Court and Public Utility Commission.
Section 25 of the Interstate Commerce Act provides in pertinent part as follows:
“Order to install systems, etc.; modification; negligence of carrier
“(b) The Commission may, after investigation, if found necessary in the public interest, order any carrier within a time specified in the order, to install the block signal system, interlocking, automatic train stop, train control, and/or cab-signal devices, and/or other similar appliances, methods, and systems intended to promote the safety of railroad operation which comply with spec*343ifieations and requirements prescribed by the Commission, upon the whole or any part of its railroad such order to be issued and published a reasonable time (as determined by the Commission) in advance of the date for its fulfillment: Provided, That block signal systems, interlocking, automatic train stop, train control, and cab-signal devices in use on August 26, 1937, or such systems or devices hereinafter installed may not be discontinued or materially modified by carriers without the approval of the Commission: . . .
“Filing report on rules, standards, and instructions with Commission; time; modification
“(e) Each carrier by railroad shall file with the Commission its rules, standards, and instructions for the installation, inspection, maintenance, and repair of the systems, devices, and appliances covered by this section within sis months after August 26, 1937, and, after approval by the Commission, such rules, standards, and instructions, with such modifications as the Commission may require, shall become obligatory upon the carrier: Provided, however, That if any such carrier shall fail to file its rules, standards, and instructions the Commission shall prepare rules, standards, and instructions for the installation, inspection, maintenance, and repair of such systems, devices, and appliances to be observed by such carrier, which rules, standards, and instructions, a copy thereof having been served on the president, chief operating officer, trustee, or receiver, of such carrier, shall be obligatory: Provided further, That such carrier may from time to time change the rules, standards, and instructions herein provided for, hut such change shall not take effect and the new rules, standards, and instructions he enforced until they shall have been filed with and approved hy the Commission:* And provided further, That the Commission may on its own motion, upon good cause shown, revise, amend, or modify the rules, standards, and instructions prescribed by it under this subsection, and as revised, amended, or modified they shall be obligatory upon the carrier after a copy thereof shall have been served as above provided.” (Emphasis marked supplied.)
On April 1, 1967 all railroad safety regulations formerly administered by tbe I.O.O. were placed under tbe aegis of tbe Department of Transportation, Federal Railroad Administration.
Order No. 29543 requires all Glass I and all switching and terminal railroads subject to the Interstate Commerce Act to install either automatic or manual block control systems on those parts of the lines where passenger trains operate at more than 60 mph, or where freight trains operate at more than 50 mph. The order further requires that if the manual block control system is used it shall be supplemented by flag protection whenever a passenger train is admitted to a block occupied by another train, or a passenger train occupies a block into which any other train seeks entry.
The Department of Transportation, by two letters dated July 6, 1967 and July 31, 1967, informed counsel for appellant railroads that this order is stiU in effect, and was adopted on April 1, 1967 by the Federal Railroad Administration. Prior to that date, the order had been followed in two cases. See In the Matter of Application for Approval of Proposed Modifications of Systems or *346Devices under Paragraph (h), Section 25 of the Interstate Commerce Act, as amended (Pennsylvania Railroad Company), 293 I.C.C. 765, 768 (1954); In the Matter of Application for Approval of Proposed Modifications of Systems or Devices under Paragraph (h), Section 25 of the Interstate Commerce Act, as amended (Pennsylvania-Reading Seashore Lines), 298 I.C.C. 503, 506 (1956).