By the middle 1880's, practically all the roads except those in
the South, were of the present standard gauge. The southern roads were
still five feet between rails.
It was decided to change the gauge of all southern roads to standard,
in one day. This remarkable piece of work was carried out on a Sunday in May
of 1886. For weeks beforehand, shops had been busy pressing wheels in on the
axles to the new and narrower gauge, to have a supply of rolling stock which
could run on the new track as soon as it was ready. Finally, on the day set,
great numbers of gangs of track layers went to work at dawn. Everywhere one
rail was loosened, moved in three and one-half inches, and spiked down in its
new position. By dark, trains from anywhere in the United States could operate
over the tracks in the South, and a free interchange of freight cars everywhere
was possible.
-- Robert Henry, "Trains", 1957