A railroad hopper car discharge outflow is controlled by closure members, at least one of which is movable. The closure members (or doors) are hingeless, being mounted on four bar linkages, such that the distal edge of the doors sweeps predominantly horizontally while the proximal edge of the door moves predominantly upwardly. The doors move through noncircular arcs, such that the size of the vertically projected door opening is abnormally large compared to the clearance heights of the door during opening and closing. The doors are driven by a transverse drive linkage that is driven by a transversely mounted actuator. The actuator may be mounted in an accommodation in the lee of slope sheets between adjacent hoppers in a mid-span portion of the car. Drive from the actuator is carried to a pair of symmetrically mounted doors through drive train linkages.