I believe it was Stalin who upgraded it from a rickety single track line into a double track line.
Since then, more lines have been laid connecting east and west.
and how often it would have to be bombed/sabotaged/destroyed at strategic intervals of a couple days apart in many places to render it totally ineffective in moving anything? Where there’s a will, there’s a way.
Experience in WW-II and even North Vietnam showed that railways could be returned to service quite rapidly (48-72 hrs max) even after massive bombardment.
I don't think any repair data exists concerning modern warfare such as aftermath of strikes by flights of B-1, B-2 and B-52 dropping looong daisy chains of JDAMS along a stretch of track.
Then there is the diruptive potential of drones.
I wonder how bunker busters would affect the repair time of railroads by massive cratering and soil destabilization?