The United States has the highest vehicle ownership per capita in the world, with 832 vehicles in operation per 1000 people in 2016. Also, China became the worlds largest new car market in 2009. In 2011, a total of 80 million cars and commercial vehicles were built, led by China which built a total of 18.4 million motor vehicles. Definitions and terminology
In 1968 the Vienna Convention on Road Traffic gave one of the first international definitions of a motor vehicle:

(o) “Power-driven vehicle” means any self-propelled road vehicle, other than a moped in the territories of Contracting Parties which do not treat mopeds as motorcycles, and other than a rail-borne vehicle;
(p) “Motor vehicle” means any power-driven vehicle which is normally used for carrying persons or goods by road or for drawing, on the road, vehicles used for the carriage of persons or goods. This term embraces trolley-buses, that is to say, vehicles connected to an electric conductor and not rail-borne. It does not cover vehicles, such as agricultural tractors, which are only incidentally used for carrying persons or goods by road or for drawing, on the road, vehicles used for the carriage of persons or goods
Other sources might provide other definitions, for instance in the year 1977, ISO 3833:1977 provide other definitions. Ownership trends
The US publisher Wards estimates that as of 2010, there were 1.015 billion motor vehicles in use in the world.
A motor vehicle, also known as motorized vehicle or automotive vehicle, is a self-propelled land vehicle, commonly wheeled, that does not operate on rails (such as trains or trams) and is used for the transportation of people or cargo. The vehicle propulsion is provided by an engine or motor, usually an internal combustion engine or an electric motor, or some combination of the two, such as hybrid electric vehicles and plug-in hybrids. For legal purpose, motor vehicles are often identified within a number of vehicle classes including cars, buses, motorcycles, off-road vehicles, light trucks and regular trucks. These classifications vary according to the legal codes of each country. ISO 3833:1977 is the standard for road vehicle types, terms and definitions. Generally, to avoid requiring people with disabilities from having to possess an operators license to use one, or requiring tags and insurance, powered wheelchairs will be specifically excluded by law from being considered motor vehicles. As of 2011, there were more than one billion motor vehicles in use in the world, excluding off-road vehicles and heavy construction equipment. The US publisher Wards estimates that as of 2019, there were 1.4 billion motor vehicles in use in the world.Global vehicle ownership per capita in 2010 was 148 vehicles in operation (VIO) per 1000 people. China has the largest motor vehicle fleet in the world, with 322 million motor vehicles registered at the end of September 2018.