This line has been in service since the Tsar's, though upgrade began in the late-20s
through mid-30s to handle more modern rail engines and rail cars that were being
acquired in Germany and the U.S. for all Soviet rail lines.
This process was generally underway on most mail line existing rail lines during the period,
including employment of American engineers (prominently used on the Trans-Siberian route).
Several of the lines, not previously double-tracked, were upgraded in this manner - allowing
in WW2 a higher traffic volume.
There are other's missing lines as well...heads-up Dax (email with graphic chart sent directly).
