Abstract: A system for operating hopper doors 14, 16 in a bulk transport vehicle comprises linkages 34, 36, 38, 40 forming an over-center locking arrangement and separate opening and closing trip levers 24, 50 attached to an operating shaft 30. The trip levers 24, 50 are operated by engaging associated cams 28, 54 as the vehicle is moved relative thereto. The cams 28, 54 are inactivated by being rotated, translated or lowered out of the path of the trip levers to a position where they do not trigger the operation of the doors 14, 16. A single door or pair of doors may be operated at the same time. To prevent false triggering of the door mechanism in transit, a secondary lock can be provided where a spring or counterweight is used to bias a lever which restrains a governor. The governor moves between stops which determine the angular positions corresponding to the door(s) 14, 16 being opened or closed.