Shippers guide

There are shipper's guides, railroad produced books of the customers they serve, available for the PRR, NYC and I think the B&O.

http://railsunlimited.ribbonrail.com/Books/shippers.html

You could use the Opsig industry database.

https://www.opsig.org/Resources/IndustryDB
the only problem is the dates are approximate. A number of companies listed in my area didn’t exist in my era and vise versa. You almost need to cross reference your information to verify. 
 

I used local information as much as possible, assuming that someone from here would probably  report the information more accurately. Google is interesting for searching specific information because often historical books for sale will contain the keyword and show up. 

yeah, shipper's directories

Most if not all of the big Class I's had them. I've seen a few, and I have C&O's for 1950 and a partial of 1934's. I never thought about it but the railroad's siding books also tell you a lot about the industries. For example, I know that the Charlottesville Woolen Mill was in operation in 1950 because it's in the shipper's directory. But I also know that there was a dairy farm from a bit upstream because it owned a small part of the Woolen Mill's siding! Likewise, many of the smaller sidings around my area had either partial or complete ownership by the industries they served. There are quite a few entries that show that C&O owned 100' of the siding and the industry owned 490' or whatever.

In my case I got all of these things (shipper's directory, siding books, etc) from the C&O Historical Society. I presume that the other big societies must have something reasonably analogous.

The PRR had a document called

The PRR had a document called the CT1000 that lists their shippers, and I believe you can still download the edition from 1945. A Google search should turn it up.

It lists all the industries located along their lines around Pittsburgh. I've been portions of i it to see what was located along the PRR up by Oil City.

Brian B.

PRR CT 1000

If you haven't been there before, this is a great site, he has the 1945 PRR CT 1000 here:

multimodalways.org,

Link

The link I provided in the first response has both the PRR CT-1000 and NYC/PLE shipper's guide for sale.