The Walking Floor system consists of groups of sets of three slats lying along the length of the truck. When a cargo is unloaded, the entire floor moves rearwards in a single motion, causing part of the cargo to fall out of the trailer. The three sets of slats then pull back one by one, so that the load remains stationary, as only a third of the floor moves at any one time. This process repeats itself until the entire cargo is unloaded.
Of course, it is also possible to reverse this process, to easily load pallets in the back of the semi-trailer, for example.