An improved rail car is pulled by an engine for transporting coal or other porous dust bearing materials. The car has opposing long sidewalls and opposing shorter end walls, which together define an initially open interior, a bottom and an open top. The open top of the car is covered by at least one pair of main doors in the form of opposing hinged A-frame sections which are pivotable between a closed, transport position and an open loading position which exposes the rail car interior for loading. The A-frame sections also have longitudinally spaced edges which are spaced apart to form a discharge door opening. A discharge door is located in each of the discharge door opening and is pivotally hinged within the respective door opening so that it opens under the influence of gravity in a rotary dumping operation. The discharge doors, together with the A-frame sections, form a door-within-a-door operating configuration.