Boxcar, 50 Foot, AAR Double Door

History: Beginning in 1932, under the auspices of the American Railway Association (merged into the AAR in 1934), the organization’s “Committee on Car Construction” set the standard for the 40-foot steel boxcar, which would undergo a series of refinements over the next 15 years or so, and on which thousands of the ubiquitous house cars would be built.

Introduced in late 1938, the modified plans included an extended interior height of 10 feet 6 inches with a new Dreadnaught end that displayed a 5/5 rib pattern, as compared to the original 1937 AAR design with its 10-foot interior height and 4/5 Dreadnaught end. The extra height gave railroads operating west of Chicago some extra cargo volume, especially handy for the grain hauling roads during harvest season, for example.

Railroad/Company: The Association of American Railroads (AAR) is an industry trade group representing primarily the major freight railroads of North America (Canada, Mexico and the United States). Amtrak and some regional commuter railroads are also members. Smaller freight railroads are typically represented by the American Short Line and Regional Railroad Association (ASLRRA), although some smaller railroads and railroad holding companies are also members of the AAR. The AAR also has two associate member programs, and most associate members are suppliers to the railroad industry.

Where appropriate, the AAR represents its members' interests to the public at large and to Congress and government regulators in particular. The AAR works to improve the efficiency, safety and service of the railroad industry, such as through its responsibility for the industry's interchange rules and equipment specifications, e.g. for locomotive multiple unit control. One of the AAR's duties is to oversee the assignment of reporting marks – two to four letter codes that uniquely identify the owner of any piece of railroad rolling stock or intermodal freight transport equipment (trailers, semi-trailers, containers, etc.) that can be carried on a railroad.

From Wikipedia