"Among urban areas, the highest auto densities are found in San Francisco-Oakland (4,000 veh/sq mi), San Jose (3,900), and Los Angeles (3,800). The New York-Northern New Jersey urban area only has about 2,200 cars per square mile, but that covers more than 3,300 square miles of land outside of Manhattan, including most of Long Island and parts of New Jersey more than 100 miles south of New York City. The Houston urban area has just 1,700 cars per square mile.
About a dozen incorporated cities and towns have higher auto densities than Manhattan, led by Guttenberg, NJ at 20,600 veh/sq mi and West Hollywood, CA at 13,900 veh/sq mi. Then there is Friendship Village, MD, the highest-density "census-defined place" in America, a small group of high rises housing 82,000 people and 45,000 cars per square mile (though in fact the whole place occupies less than a tenth of a square mile). In general, higher population densities may have lower auto ownership rates but they are still tend to be associated with higher auto densities per square mile. So much for reducing congestion by increasing population densities."
O'Toole's analysis points to relatively low rates of auto ownership in high density areas, but suggests that these areas have disproportionately high concentrations of cars that create the conditions for traffic congestion.