Wikipedia
RailBox Company , founded in 1974, was created to address a boxcar shortage in the United States in the 1970s.
The concept behind RailBox, as evidenced by their slogan "Next Load, Any Road!" was that since Railbox was owned by many of the railroads as a privately owned cooperative, their boxcars were not subject to load/empty rules. Railbox cars could be assigned for service anywhere in Canada, Mexico and the United States on lines where an AAR Plate-C loading gauge is permitted. Railbox purchased boxcars from many Manufacturers including American Car and Foundry (ACF), Farmers Machinery Company (FMC), and Pullman-Standard (P-S).
Under the ICC car routing rules in effect at the time, cars owned by operating companies were supposed to be routed back to their owning road as soon as possible or the host road would have to pay demurrage(car storage and handling) charges. This was the cause a shortage of available cars and not an actual shortage of boxcars numerically. As empty cars were required to be routed back to their home railroad instead of being loaded and routed to another destination.
RailBox cars are all boxcars and are painted yellow with black doors. Railbox cars had a bold graphic side logo, which was a stylized X made of red and blue intertwined arrows to symbolize free flow. During the 1970s many railroads had old fleets of railcars. Due to the poor financial state of many railroads these cars were dirty and grimy. Railbox cars stood out with their bright yellow paint and large logos. The company's car reporting marks, as noted above, ended in the letter "X". Under FRA designation reporting marks ending in "X" are assigned to private owner cars.
As of 2015, many RailBox cars are still in service. The rise of intermodal containerized freight (which began in the late 1980s and early 1990s) has reduced the demand for full carload boxcar service. Also deregulation in the 1980s eliminated the legacy car routing rules, reaching its peak with the elimination of the Interstate Commerce Commission in 1995.
RailBox (and the similar Railgon Company) are currently subsidiaries of TTX Company.