Open Hopper, 3-Bay, 70 Ton Offset

History: 70 ton 3-bay offset side hoppers first appeared in the late 20s and by the late 30s had become an AAR standard design with cars being delivered from a number of builders in large quantities to railroads across the country. The last of these cars were delivered in the mid-'60s and many remained in service through the 80s.

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