I've analyzed the same conductor's train book I mentioned earlier, this time for the 139 box cars in the sample. This isn't a very big sample, but it does yield some interesting conclusions. I've summarized them in a blog post, at

http://modelingthesp.blogspot.com/2011/03/modeling-freight-traffic-coast-line_11.html .

The main thing I think I can get from the data is that about a third of all the box cars in the sample were home-road cars (SP + T&NO), which is about what I'd concluded from counting cars in photos of yards and trains. Perhaps also noteworthy is that PRR cars were represented at about their percentage in the national car fleet, but some other roads were notably under- or over-represented, in Gilbert- Nelson terms. I personally do not attach much importance to that conclusion, however, because the sample is pretty small for most roads.

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