Very interesting chart. As general background, there has been very little change in rail car or truck trailer per-capita capacity, (either by weight or by volume) between 2007 and the present. From the chart:
Box car numbers way down, whether plain, equipped or refrigerated, (because of the change to intermodal and/or Piggyback).
Hopper car numbers are down, (because steam coal tonnage is down because of cheap Wind, Solar and Frack Gas are way up).
Covered hopper numbers are up some, (because commodities tonnage is always increasing incrementally).
Tank car numbers way up, (to haul Frack Oil).
