Rail freight uses many types of goods wagon (UIC) or freight car (US). These include box cars (US) or covered wagons (UIC) for general merchandise, flat cars (US) or flat wagons (UIC) for heavy or bulky loads, well wagons or "low loader" wagons for transporting road vehicles; there are refrigerator vans for transporting food, simple types of open-topped wagons for transporting bulk material, such as minerals and coal, and tankers for transporting liquids and gases. Most coal and aggregates are moved in hopper wagons or gondolas (US) or open wagons (UIC) that can be filled and discharged rapidly, to enable efficient handling of the materials.