floor of the truck's trailer. Some buildings only have drive-in doors, i.e. doors at the same level as the ground outside of the building, suitable for driving directly into the building. For loading docks with drive-in doors, and also (albeit rarely) for loading docks with truck-level doors, a lift is sometimes employed. Other, less common, devices employed when bridging the gap between truck and dock are truck levelers. These are hydraulic lifts positioned beneath the rear wheels of the truck, that are used to raise and lower the truck so that it is level with the loading dock edge. The problems with truck levelers, that make them rarely employed, are twofold. First: They cause the truck interior to be at an incline, which causes loading and unloading difficulties. Second: They are expensive to maintain, since they require (being below ground level and open to the air) proper drainage and protection against the weather. Recessed dock levelers also have problems of exposure to the weather. However, because they are recessed into the dock, which is above ground level, they do not have as great a problem with drainage. Equally, because they are recessed into the dock, they extend partially back from the dock edge. A dock leveler can be installed so that it extends inside the loading dock door, and thus inside the building, protecting it from the weather. References Warehouses Trucks