Choosing a model car fleet -- some numbers

I have discussed in previous posts the broad problem of choosing a realistic and prototypical fleet of model freight cars. Getting more specific about quantities is an interesting problem with several dimensions. In order to have a particular example, I will postulate someone with a layout on which there are going to be 400 freight cars. How many of them should be home road cars (and which types)? How many should be foreign cars from particular railroads (and which types)? I am certain there are no global answers for these questions, and considerable research might be required for any specific case—if one wishes to be prototypical. (I’m as guilty as anyone of those impulse purchases, but I always try to sit down and wait for the impulse to pass.) So how can I approach these home and foreign car problems?
     First, home-road cars—that’s a long-standing problem and likely one which varies from railroad to railroad, and from place to place on most railroads. Back around 1940, Al Kalmbach, writing a column under the name “Boomer Pete,” suggested these proportions: half home-road cars, one-fourth cars from roads with direct connections to the home road, and one-fourth cars from all other railroads. I will return in a moment to the foreign cars, but I am sure that Al Kalmbach based his one-half suggestion for the home road on observation of the prototype. He lived in Milwaukee and likely what he saw around him was half home-road cars. But that might not be true in Milwaukee today, and perhaps not true in 1940 in other areas.
     Anyhow, rather than try to draw general conclusions about this hypothetical 400-car fleet of model cars, I will do an illustrative set of calculations as though the cars were for my layout, set on Southern Pacific’s Coast Line in 1953. I will also have to divide the story into two parts, first the home-road cars, and then the identification of foreign cars mostly in a second post. So let me begin with the home-road part.
     Awhile back, I posted part of my analysis of a conductor’s time book for the SP Coast Line, from 1948–1952, near the time I model. Among all box cars in that time book sample, home-road cars (SP plus T&NO, which were freely shared) were 36% of the total. That post, with more details, can be seen at: http://modelingthesp.blogspot.com/2011/03/modeling-freight-traffic-coast-line_11.html . If I were to stick to this value for an entire fleet, such as the 400 cars mentioned above, that would amount to 144 SP cars among the 400 cars. But of course my 36% number is only for box cars, not for all car types, so that would be too simplistic an answer.
     So how do we get at car types? To address this question for both home-road and foreign cars, I have to show some data, which may be more digestible in the form of bar graphs. These are data for 1950, from the Official Railway Equipment Register or ORER; one chart is for the entire nation, the other for Southern Pacific. Actual percentages are shown above each bar, for those who want the underlying data (you may click to enlarge).

One advantage of bar graphs like these is that it is immediately evident that the two graphs, despite identical axes, look quite different: and of course the two car fleets are quite different.
     Both these graphs are for rather global sets of cars. The SP was a single railroad, but it extended from Portland, Oregon to Ogden, Utah and New Orleans, across an extremely varied geographic territory. Cars which would be seen in any one place on the SP, such as San Luis Obispo, would be unlikely to follow the chart shown above exactly. But the challenge is, we don’t have information about what division of car types did exist at any specific locales.
     I’m now going to make a pretty blue-sky guess, though one which may be in the general ballpark of actuality. I’m going to guess that the SP car fleet, as shown in the graph above, reflected the total traffic pattern on the SP. After all, that’s why they owned the cars they did. That can’t be exactly right, because incoming traffic may not mirror the on-line traffic for which SP chose to supply cars, but it may be in the right direction, at least, and anyway, there isn’t any better answer that I know of.
     Returning to the question of those SP home-road cars in the 400-car fleet I postulated, obviously we should see a major preponderance of box cars, followed by gondolas, with other types well back. In fact, adding box and gondola types together gives about 75%, or three in every four SP cars. I’ll start with box cars, which were 56% of the SP fleet, which would constitute 224 of the 400 total cars under my use of SP fleet proportions for all cars. Then there should be (as I said above) 36% SP and T&NO cars, or 81 cars. The balance of the box cars, 176 cars, will be foreign cars, about which more in a moment.
     What else? Note that the SP chart shows zero reefers, because the supply of such cars to SP was from Pacific Fruit Express, jointly owned with UP, and not in the form of SP-owned cars. But of course there was plenty of perishable traffic throughout the SP. In particular, I would expect a lot of refrigerator cars on the Coast Line, and indeed one reason I chose it to model is for exactly that traffic.
     Total refrigerator car numbers from train and yard photos on the Coast appear to range around 10 to 20% of all freight cars, which means 40 to 80 cars in a 400-car fleet. As I mentioned in analyzing that Coast Line time book, the total reefer population at harvest time was only 76% PFE, the rest foreign cars. (You can read my analysis of Coast Line reefers in harvest season in the post at: http://modelingthesp.blogspot.com/2011/02/modeling-freight-traffic-coast-line.html .) Applying that percentage to the 400-car fleet with 10 to 20% reefers would mean 30 to 60 PFE cars. That would also mean 10 to 20 foreign reefers (when I’m modeling operation in harvest season—otherwise it would be close to 100% PFE cars, exclusive of meat cars).
     So far I have chosen 224 box cars, of which 81 should be SP and T&NO, and about 45 PFE reefers plus perhaps 15 foreign reefers. This totals to 284 of the 400 cars in my postulated fleet. What makes up the remaining 116 cars? Obviously gondolas should be a major part, along with tank cars (note they are 8% of the national fleet, shown above) and on the SP, flat cars ought to be comparable to tank cars. Proportioning these remaining car types among those 116 cars gives about 70 gondolas, 18 tank cars, 12 flat cars, 8 stock cars and 8 hoppers (mostly longitudinal-dumping ballast cars on the SP). And we know that the flat cars and gondolas will be predominantly SP ownership.
     That brings me to the foreign-car part of the problem, which I will postpone to a future post, since this one is already getting kind of long and complicated. But I hope this discussion, largely restricted to the home-road part of the topic, illuminates one way of approaching the problem of being quantitative in choosing a model freight car fleet.
Tony Thompson