Car carriers are special built vessels that are able to transport cars in a manner where they are stored in a garage with ambient control and ventilation. The largest car carriers can transport up to 7.000 units. Such vessels have a construction as a very efficient parking house that are able to propel itself on water. There are several level of internal decks with ramps system to elevate cars up and down to a berth. A large car carrier would typically have a ship crew of about 20 people on board, and has a service speed of 16-18 knots.