Hi Chris,
This might have been an auxhilary power generator... On the roof of the boxcar towards the left side, there appears to be what might be an exhaust stack.
It looks to wide to be a smoke jack for a heater....
The boxcar may contain a diesel engine and generator for producing emergency power if there was a problem with local power or overhead damage...
Just park the boxcar on a siding and fire up the generator. Put up the pan and feed juice to a section of the mainline....