There are single-layer and double-layer passenger cars; there are articulated and towed models. There are two doors, single door, or luggage compartment. Most passenger cars are driven by diesel engines. At present, there are also pure electric vehicles and all-metal bodies. According to the energy consumption and road area occupied by the number of passengers, public transportation vehicles are more economical than personal vehicles. This is one of the main reasons for the priority of developing public transportation buses in many countries. From a global perspective, the manufacture and popularization of cars are relatively extensive.