I didn't have specific traffic documentation. So I took the two dozen or so NH-related books I have, documented the freight makeup in all the photos and derived my roster composition from that. I have the overall breakdown by road as well as breakdown by body type. I try to stick closely to the numbers, so when a new piece of equipment is acquired, an old piece is retired. My percentages are roughly this:
[ Guests cannot view attachments ]
Pennsy had a significant freight equipment presence as well as passenger equipment, so I categorize PRR individually as with NH. "Direct" refers to roads that NH directly interchanged with such as NYC, Erie, L&HR, CV, B&M, etc. This also includes private companies such as Swift and Narragansett that had major plants on NH routes, as well as companies with NH ownership such as FGE. "Indirect" refers to roads in close proximity that didn't interchange directly with NH but did with roads that interchanged with NH. "Other" is all foreign equipment from roads outside of the region such as ATSF and UP, as well as the remaining private companies. "Non-Revenue" consists mostly of cabooses. Some categories get stretched a little, such as Stockcars where I should have only two cars in total but I have four. I also tend to have at least one each of the N scale models that are of specific prototypes and specific roads and era-appropriate, such as InterMountain’s ATSF stockcar and Fox Valley’s MILW ribbed boxcar. But I stick to the percentages for the most part.
I have a similar chart for the Conrail 1980 era as well.