building supplies such as dimensional lumber, wallboard, and fence posts. They are essentially bulkhead flatcars that have been reinforced by a longitudinal I-beam, often in the form of a Vierendeel truss, sometimes reinforced by diagonal members, but originally in the form of stressed panels perforated by panel-lightening "opera windows", either oval-shaped (seen above) or egg-shaped. These flatcars must be loaded symmetrically, with half of the payload on one side of the centerbeam and half on the other, to avoid tipping over. Heavy capacity flatcars Heavy capacity flatcars are cars designed to carry more than . They often have more than the typical North American standard of four axles (one two-axle truck at each end), and may have a depressed center to handle excess-height loads as well as two trucks of three axles each (one at each end) or four trucks (two at each end) of two axles each, connected by span bolsters. Loads typically handled include electrical power equipment and large industrial production machinery. Circus use A circus train is a modern method of conveyance for circus troupes. One of the larger users of circus trains was the Ringling Bros. and Barnum & Bailey Circus (RBBX), a famous American circus formed when the Ringling Brothers Circus purchased the Barnum and Bailey Circus in 1907, merged in 1919, and closed permanently as a merged company in May 2017. Remote control use Some companies, such as CSX Transportation, have former wood-carrying flatcars rebuilt into platforms which mount remote control equipment for use in operating locomotives. Such platforms are fitted with appropriate headlights, horns, and air brake appliances to operate in the leading position on a cut of cars (i.e. coupled ahead of the locomotive). Intermodal freight use COFC (container on flat car) cars are typically long and carry four intermodal containers or two / shipping containers (the two containers are carryable due to the fact that the car is actually long, over the strike plates). With the rise of intermodal-freight-transport–specific cars, and given the age of most of these flats, numbers will decline over the next several years. Indeed, when the first well cars appeared, allowing double stacking, many container flats were re-built as autoracks. The few "new build" container flats are identifiable by their lack of decking, welded steel frame, and standard length. One variant is the car (which usually carries one large container as a load); these are actually re-built