I touched on this in my post about Upgrading old models, in suggesting that the numbers of prototype car classes should guide the numbers of cars you model. In this post I go farther with that idea, choosing a specific prototype car important to my layout: Pacific Fruit Express refrigerator cars.
I realized some time ago that the PFE car fleet, totaling about 40,000 cars in the era I model (1953), could be modeled by doing 1 car on my layout for each group of 1000 prototype cars, meaning I’d have about 40 PFE models when I was done. This was a big number but not unreasonable for my total car needs and space.
Then the choices of cars and car classes is fairly easy. I simply looked at the 1953 Official Railway Equipment Register or ORER (conveniently available as an NMRA reprint) and tabulated the PFE fleet, omitting very small car groups as well as a few unusual cars which might be hard to model. I listed rebuild car classes by both capacities, so “R-30/40-19” means the combination of R-30-19 and R-40-19 cars. Here’s the result.
I probably won’t stick to this division by car classes rigorously (I already have too many InterMountain Class R-40-23 cars), but this definitely provides guidance in what to build or buy, and almost more important, what not to build or buy.
This same approach can be used in a bigger arena by identifying which freight cars one needs from foreign roads across the country, but I’ll save that for a future discussion.