Drive in system is used in high density storage with limited code numbers (pallets of the same type per shelf tunnel). The trucks go into the shelves to load or unload pallets, which are stored on rails.
The first pallet to go through the system first is, usually, the last one to go out (LIFO). There is also the possibility of a drive-through system creation, by creating aisles on both sides of the construction. This way, the first pallet to go in the system, is the one that will also come out first.