I have shown a couple of times on this blog the list I made of AAR code numbers for “selected railroads,” which are the numbers shown next to railroad names on waybills and other accounting documents. These numbers were assigned by the AAR and were mandatory for use on AAR forms such as waybills. But the “selected” names I chose are a small fraction of all the railroads in the AAR list. This post provides a link to the complete list.
I have scanned the 15 pages of the list from the AAR book Railway Accounting Rules (1950 edition--numerous editions exist), and provided a PDF document on Google Docs. Here is a link to that document: https://docs.google.com/file/d/0Bz_ctrHrDz4wZ2NjTU92aG9Id00/edit
Thus in a form like the one below, which is a corrected waybill from the Detroit, Toledo & Ironton, the code number, alongside the railroad name at the top of the document, is 208.
But if you don’t have such a form, which would give you the code number for that particular railroad, simply consult the AAR list provided above.