ion of the
evidence and the detailed findings makes it clear that this conclusion
was rested on facts found which indicate that such increased danger of
accident and personal injury as may result from the greater length of
trains is more than offset by the increase in the number of accidents
resulting from the larger number of trains when train lengths are
reduced. In considering the effect of the statute as a safety measure,
therefore, the factor of controlling significance for present purposes
is not whether there is basis for the conclusion of the Arizona Supreme
Court that the increase in length of trains beyond the statutory maximum
has an adverse effect upon safety of operation. The decisive question is
whether in the circumstances the total effect of the law as a safety
measure in reducing accidents and casualties is so slight or
problematical as not to outweigh the national interest in keeping
interstate commerce free from interferences which seriously impede it
and subject it to local regulation which does not have a uniform effect
on the interstate train journey which it interrupts."[823]

THE LESSON OF SOUTHERN PACIFIC CO. _v._ ARIZONA

The lesson to be extracted from Southern Pacific Co. _v._ Arizona is a
threefold one: 1) Where uniformity is judged by the Court to be
"essential for the functioning of commerce, a State may not interpose
its regulation"; 2) in resolving this question the Court will canvass
what it considers to be relevant facts extensively; 3) its task is,
however, in the last analysis, one of weighing competing values, in
brief, arbitral rather than strictly judicial.

The lesson of Southern Pacific is further exemplified by the more recent
holding in Morgan _v._ Virginia,[824] in which the Court was confronted
with a State statute which, in providing for the segregation of white
and colored passengers, required passengers to change seats from time to
time as might become necessary to increase the number of seats available
to the one race or the other. First, reciting the rule of uniformity,
Justice Heed, for the Court, said: "Congress, within the limits of the
Fifth Amendment, has authority to burden [interstate] commerce if that
seems to it a desirable means of accomplishing a permitted end. * * *
As no State law can reach beyond its own border nor bar transportation
of passengers across its boundaries, diverse seating requirements for
the races in interstate journeys result. As there