Freight elevators are generally required to display a written notice in the car that the use by passengers is prohibited (though not necessarily illegal), though certain freight elevators allow dual use through the use of an inconspicuous riser. Freight elevators are typically larger and capable of carrying heavier loads than a passenger elevator, generally from 2,300 to 4,500 kg. Freight elevators may have manually operated doors, and often have rugged interior finishes cab (which called enclosure) to prevent damage while loading and unloading. Although hydraulic freight elevators exist, traction elevators are more energy efficient for the work of freight lifting. These elevators are specially constructed to withstand the rigors of heavy loads. Classes of Freight Elevator Class A: General Freight Loading Freight elevator with this class has the load distributed, the weight of any single piece is not more than 1/4 the capacity of the elevator and the load is handled on and off the car platform manually or by means of hand trucks. Class B: Motor Vehicle Loading Freight elevator with this class is used solely to carry automobile trucks or passenger automobiles up to the rated capacity of the elevator. Class C1: Industrial Truck Loading A four-wheeled vehicle may be used to load and unload in the elevator with this class. The combined weight of the vehicle and the load cannot exceed the rated capacity and may be rolled onto the platform as a single unit. Class C2: Industrial Truck Loading In this class, during loading and unloading, the maximum load on the platform may be up to 150% of the rated capacity. This enables the user to use a forklift to load a car with freight weighing up to the rated capacity. Class C3: Other forms of Industrial Truck Loading During the loading and unloading process, the rated capacity.