The AAR Mechanical Designations

Designations of freight cars to describe their suitability for different cargoes have a long history. The American Railway Association (ARA), predecessor of the Association of American Railroads (AAR) was printing them in the back of Official Railway Equipment Registers (ORER) at least as early as March 1923 (the oldest ORER issue I have), and they continued to be so printed at least as late as July 1970 (the newest ORER I have).

What did these listings contain? They comprise descriptions of different freight car characteristics, and two-letter or three-letter designation codes for each. Some of these are so familiar as to require no explanation, such as “XM” for ordinary box cars. Others, such as RSM, may draw a blank. That designation happens to describe a meat reefer; here is the listing for RSM, and the more general ice reefer designation, RS.

An example of such an RSM car is shown below, modeled by upgrading the ancient Varney/LifeLike plastic reefer, as I described in a series of posts (see for example this one: https://modelingthesp.blogspot.com/2013/05/modeling-meat-reefers-part-5.html ).

Modelers of earlier eras tend to know these codes; but modelers more recently in the hobby, or those modeling more recent eras, often give you a blank look if you refer to them. I thought it might be useful to make them available. More than a dozen years ago, I posted an introduction to this subject (see that post at: https://modelingthesp.blogspot.com/2011/09/aar-car-types.html ) and now am going further by making the entire listing available.

I have scanned these definitions from the back of the January 1953 ORER, made up a five-page PDF, and posted it in Google Docs for anyone to access.  You can find it at: https://drive.google.com/file/d/1XbupnOIXC9RVpFvPAyf-xwDX8Saz9yot/view?usp=drive_link .

A complication to keep in mind when looking at the designations is that one needs to read even the footnotes in the designation pages. An example is the flat car listing, shown below: see Note 1 at the bottom.

It is only a small note at the base of the entry, but it is essentially the new designation for bulkhead flat cars, FMS, that is described. This designation remained as a footnote for years, even as bulkhead flat cars became commonplace on mainline railroads. 

This is of interest to me because the Southern Pacific began building such cars in its own shops as early as 1949, and the SP Historical & Technical Society issued parts to add bulkheads to the accurate Red Caboose SP Class F-70-7 flat car. Subsequently Red Caboose issued ready-to-run models of these cars, using the Society bulkheads. The photo below by the late Paul Lyons illustrates one of these models.

I make use of these designations in operating my layout. They are included on waybills, as shown below, to help operators recognize cars and spot them at industries correctly when necessary, though  the AAR’s prototype waybill form did not include the AAR designations.

 So to me, the AAR designations or codes are cool, informative, prototypical, and useful. I enjoy including them in layout operations.

Tony Thompson