merce is for her benefit on a criminal trial for violation of the challenged statute. Hatch v. Reardon, 204 U. S. 152, 160; Federation of Labor v. McAdory, 325 U. S. 450, 463.

This Court frequently must determine the validity of state statutes that are attacked as unconstitutional interferences with the national power over interstate commerce. This appeal presents that question as to a statute that compels racial segregation of interstate passengers in vehicles moving interstate.12

The precise degree of a permissible restriction on state power cannot be fixed generally or indeed not even for one kind of state legislation, such as taxation or health or safety.13 There is a recognized abstract principle, however, that may be taken as a postulate for testing whether particular state legislation in the absence of action by Congress is beyond state power. This is that the state legislation is invalid if it unduly burdens that commerce in matters where uniformity is necessary-necessary in the constitutional sense of useful in accomplishing a permitted purpose." Where uniformity is essential for the functioning of commerce, a state may not interpose its local regulation.15 Too true it is that the principle lacks in precision. Although the quality of such a principle is abstract, its application to the facts of a situation created by the attempted enforcement of a statute brings about a specific determination as to whether or not the statute

12 When passing upon a rule of a carrier that required segregation of an interstate passenger, this Court said, "And we must keep in mind that we are not dealing with the law of a State attempting a regulation of interstate commerce beyond its power to make." Chiles v. Chesapeake & Ohio R. Co., 218 U. S. 71, 75.

13 Cf. Gwin, White & Prince v. Henneford, 305 U. S. 434, 439; Mintz v. Baldwin, 289 U. S. 346, 352; Welch Co. v. New Hampshire, 306 U.S. 79, 84.

14 Southern Pacific Co. v. Arizona, 325 U. S. 761, 766-71.

15 Cooley v. Board of Wardens, 12 How. 299, 319; Minnesota Rate Cases, 230 U. S. 352, 402; Kelly v. Washington, 302 U. S. 1, 10.

in question is a burden on commerce. Within the broad limits of the principle, the cases turn on their own facts.

In the field of transportation, there has been a series of decisions which hold that where Congress has not acted and although the state statute affects interstate commerce, a state may validly enact legislation which has predominantly only a local influence on the course of commerce.' 16 It is equally well settled that, even where Con

16 Statutes or orders dealing with safety of operations: Smith v. Alabama, 124 U. S. 465 (Alabama statute requiring an examination and license of train engineers before operating in the state); Nashville, C. & St. L. R. Co. v. Alabama, 128 U. S. 96 (statute requiring examination of railroad employees as to vision and color blindness); New York, N. H. & H. R. Co. v. New York, 165 U. S. 628 (New York statute forbidding the use of furnaces or stoves in passenger cars and requiring guard-posts on railroad bridges); Erb v. Morasch, 177 U. S. 584 (municipal ordinance limiting speed of trains in city to 6 miles an hour); Atlantic Coast Line R. Co. v. Georgia, 234 U. S. 280 (Georgia statute requiring electric headlights on locomotives); Morris v. Duby, 274 U. S. 135 (weight restrictions on motor carriers imposed by order of Oregon highway commission); Sproles v. Binford, 286 U. S. 374 (size and weight restrictions on trucks imposed by Texas statute); South Carolina Highway Dept. v. Barnwell Bros., 303 U. S. 177 (statute restricting weight and size of motor carriers); Maurer v. Hamilton, 309 U. S. 598 (Pennsylvania statute forbidding the use of its highways to any vehicle carrying any other vehicle over the head of the operator of the vehicle); Terminal Assn. v. Trainmen, 318 U. S. 1 (Illinois statute requiring cabooses on freight trains).

Statutes or orders requiring local train service: Gladson v. Minnesota, 166 U. S. 427 (state statute requiring intrastate train to stop at county seat to take on and discharge passengers); Lake Shore & Michigan Southern R. Co. v. Ohio, 173 U. S. 285 (statute requiring three trains daily, if so many are run, to stop at each city containing over 3,000 inhabitants as applied to interstate trains); Atlantic Coast Line R. Co. v. North Carolina Corporation Comm'n, 206 U. S. 1 (order regulating train service, particularly requiring train to permit connection with through trains at junction point); Missouri Pacific R. Co.

gress has not acted, state legislation or a final court order is invalid which materially affects interstate commerce."

v. Kansas, 216 U. S. 262 (order directing the operation of intrastate passenger train service over specified route).

Statutes dealing with employment of labor-full crew laws: Chicago, R. I. & P. R. Co. v. Arkansas, 219 U. S. 453 (Arkansas full crew law applied to interstate trains); St. Louis, I. M. & S. R. Co. v. Arkansas, 240 U. S. 518 (Arkansas full crew laws applied to switching crews); Missouri Pacific R. Co. v. Norwood, 283 U. S. 249 (Arkansas full crew laws applied to freight and switching crews).

17 Statutes or orders dealing with safety of operations: Kansas City Southern R. Co. v. Kaw Valley Dist., 233 U. S. 75 (order requiring railroad to remove its bridges over river for flood control purposes); South Covington & Cincinnati R. Co. v. Covington, 235 U. S. 537 (ordinances regulating the number of passengers to be carried in, the number of cars to be run and the temperature of an interstate street railway car invalid; those requiring rails on front and rear platform, ventilation and cleaning valid); Seaboard Air Line R. Co. v. Blackwell, 244 U. S. 310 (Georgia Blow Post Law requiring train to blow whistle and slow down almost to a stop at each grade crossing where numerous grade crossings were involved. Cf. Southern R. Co. v. King, 217 U. S. 524, where answer held insufficient to permit proof of burden of the statute on interstate commerce); Southern Pacific Co. v. Arizona, 325 U. S. 761 (statute limiting number of cars in freight train to 70 and passenger cars to 14).

Statutes or orders requiring local train service: Illinois Central R. Co. v. Illinois, 163 U. S. 142 (statute applied to require fast mail train to detour from main line in order to stop at station for the taking on and discharge of passengers); Cleveland, C., C. & St. L. R. Co. v. Illinois, 177 U. S. 514 (Illinois statute requiring interstate train to stop at each station); Mississippi Railroad Comm'n v. Illinois Central R. Co., 203 U. S. 335 (order of commission requiring interstate train to stop at small town); Atlantic Coast Line v. Wharton, 207 U. S. 328 (South Carolina statute and railroad commission order requiring interstate train to stop at small town); St. Louis Southwestern R. Co. v. Arkansas, 217 U. S. 136 (statute and order requiring delivery of freight cars to local shippers); Herndon v. Chicago, R. I. & P. R. Co., 218 U. S. 135 (statute requiring interstate train to stop at junction point); Chicago, B. & Q. R. Co. v. Wisconsin Railroad Comm'n, 237 U. S. 220

Opinion of the Court.

328 U.S.

Because the Constitution puts the ultimate power to regulate commerce in Congress, rather than the states, the degree of state legislation's interference with that commerce may be weighed by federal courts to determine whether the burden makes the statute unconstitutional.18 The courts could not invalidate federal legislation for the same reason because Congress, within the limits of the Fifth Amendment, has authority to burden commerce if that seems to it a desirable means of accomplishing a permitted end.19

11 20

This statute is attacked on the ground that it imposes undue burdens on interstate commerce. It is said by the Court of Appeals to have been passed in the exercise of the state's police power to avoid friction between the races. But this Court pointed out years ago "that a State cannot avoid the operation of this rule by simply invoking the convenient apologetics of the police power. Burdens upon commerce are those actions of a state which directly "impair the usefulness of its facilities for such traffic." " That impairment, we think, may arise from other causes than costs or long delays. A burden may arise from a state statute which requires interstate passengers to order (Wisconsin statute requiring interstate train to stop at villages containing 200 or more inhabitants); Missouri, K. & T. R. Co. v. Texas, 245 U. S. 484 (order requiring trains to start on time and fixing time allowed for stops at junctions en route); St. Louis & S. F. R. Co. v. Public Service Comm'n, 254 U. S. 535 (order requiring through trains to detour through a small town); St. Louis-San Francisco R. Co. v. Public Service Comm'n, 261 U. S. 369 (order requiring that interstate trains be stopped at small town).

18 See Southern Pacific Co. v. Arizona, 325 U. S. at 770.

19 Compare United States v. Carolene Products Co., 304 U. S. 144, 146.

20 Kansas City Southern R. Co. v. Kaw Valley Dist., 233 U. S. 75, 79.

21 Illinois Central R. Co. v. Illinois, 163 U. S. 142, 154.

their movements on the vehicle in accordance with local rather than national requirements.

On appellant's journey, this statute required that she sit in designated seats in Virginia.22 Changes in seat designation might be made "at any time" during the journey when "necessary or proper for the comfort and convenience of passengers." This occurred in this instance. Upon such change of designation, the statute authorizes the operator of the vehicle to require, as he did here, "any passenger to change his or her seat as it may be necessary or proper. An interstate passenger must if necessary repeatedly shift seats while moving in Virginia to meet the seating requirements of the changing passenger group. On arrival at the District of Columbia line, the appellant would have had freedom to occupy any available seat and so to the end of her journey.

23

Interstate passengers traveling via motor buses between the north and south or the east and west may pass through Virginia on through lines in the day or in the night. The large buses approach the comfort of pullmans and have seats convenient for rest. On such interstate journeys the enforcement of the requirements for reseating would be disturbing.

Appellant's argument, properly we think, includes facts bearing on interstate motor transportation beyond those immediately involved in this journey under the Virginia statutory regulations. To appraise the weight of the burden of the Virginia statute on interstate commerce, related statutes of other states are important to show whether there are cumulative effects which may make

22 The Virginia Code of 1942, § 67, defines a colored person, for the purpose of the Code, as follows: "Every person in whom there is ascertainable any negro blood shall be deemed and taken to be a colored person Provisions for vital statistics make a record of the racial lines of Virginia inhabitants. §§ 1574 and 5099a.

23 § 4097bb.