Abstract: The trailer chassis of a tractor-trailer is provided with a dumping apparatus for interchangeable shipping containers, operable to dump the contents of the container or to unload the container itself, and optionally to reload containers onto the chassis. The chassis is divided into fore and aft sections articulated on a horizontal axis at a knuckle which will bend only in a direction causing the chassis to form a hump. The knuckle is located forward of the center of gravity of the container, whereby the container remains on the aft section during dumping. A pivotable king pin plate is provided between the fore section of the trailer chassis and the tractor, avoiding stress on the king pin assembly when inclined. Vertical pins are preferably provided at each corner of the trailer chassis, the rear pins being controllably retractable for releasing the shipping container if the container itself is to be unloaded from the chassis.