Boxcar, 50 Foot, AAR

History: The AAR standard 50-ton, 50'-6" boxcar was based on a design introduced in 1942. Although World War II slowed production of these cars, thousands of similar cars were built through the 1950s. Although the cars were constructed to basically the same design, several options were offered depending on the intended service. Since production of the basic design went on for so long several changes were made, so roof styles, ends, side sills, and doors varied over time and from railroad to railroad.

The standard design featured 16-panel (8/8, for eight panels on each side of the door opening) riveted sides with an eight-foot door opening for merchandise boxcars. The automobile car version of the car featured 5/8 riveted sides with a 15-foot door opening covered with a set of two doors. All told more than 9,000 cars were built for 16 railroads to this basic design between 1950 and 1960.

The majority of 50-foot AAR cars built in the 1940s and '50s featured R+¾ improved Dreadnaught ends.

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