Indeed, what happened after WWII was a mass migration of heavy industry away
from the eastern states (where industry had originally developed) to "greenfield"
developments everywhere else. If you follow car loadings after WWII up to the PRR-NYC
merger, you see a steady (sometimes steep) drop in car loadings on those eastern roads
and a steady rise for other roads (SP, Southern, others). At one point in the 1950's
I recall SP bragging that a new rail-served customer was being added every day. In the
case of the PRR it was probably losing one every day. I figured it out once but at
some point in the 1960's the SP's revenue-ton-miles exceeded those of the PRR+NYC for
the first time.

Tim O'