Sounds odd , as if everyone of legal driving age surely must have one. Many households I know have sometimes two or three vehicles with multiple drivers under the roof.
I drive a PT Cruiser, my wife has a Prius and my brother-in-law a new, jet black Porsche. Every adult I know has a car.
That said, just under 9% of the world's population has a car.
It is a little difficult to then do simple math and say there are 6.76 billion people in the world (according to the US Census Bureau) so 600 million / 6.76 billion = about 9% of the world owns a car.
So many things we take for granted are privileges of being employed and living in the United States