Although I generally agree with the Gilbert-Nelson approach, along with Bruce Smith’s percentages, they are very dependent upon the road you model.
Bruce models the PRR, so 75% home road hoppers on any coal hauling road makes sense. But I model the NH that has a modest fleet of hoppers of less than 1,000, with little originating traffic that would send them offline. So home road hoppers make up a very small part of my fleet.
Understanding your road’s traffic is very important. For example, as much as 60% of the coal entering CT in my era was by water. That appears to have been Pocahontas and other bituminous coming through Baltimore, and I think was the primary source of coal loaded in NH hoppers to be distributed to industry, but particularly the railroad’s facilities. On the other hand, anthracite came primarily via Maybrook, unless you were in the vicinity of NYC, in which case it came mostly by float via Jersey City and Greenville. So I go with the anthracite hoppers as a mix of 75% home road of their loading point.
So the mix of hoppers is very dependent on whether you’re modeling a coal road or not, I think.
Gondolas and flats are the same, and since the NH was heavily involved in manufacturing, gondolas were also predominantly foreign. Like the hoppers, I think gondolas and flats are far more dependent on the home road of the loading point.
I also think we often have too little variety (and too few) “rare” cars. I have two pictures, from different days, with ATSF Ga-8 gons, and these weren’t photographed because of their rarity, they just happened to be on those trains. Likewise the photos of the Litchfield & Madison gondola in New Britain. Numerous pictures of C&I hoppers, etc.
I’m not saying those happen every day, but based on those and many, many other photos that have “rare” cars (often in the background) show that there’s a wider variety than many allow. I think we often make the mistake of not having enough different “rare” cars to mix in, making the couple of rare cars that are owned very common on our layouts.
Modeling the New Haven Railroad 1946-1954