Complex sentence: Automobile ownership in the United States is widespread, with most households owning one or more private auto. However car ownership rates are much lower in a number of older and larger cities where population density and public transportation access is greater.
Split into simpler sentences: Automobile ownership in the United States is widespread, with most households owning one or more private car. However, car ownership rates are relatively lower in several (mostly older and larger) cities where population density and public transportation access is greater.