"In the United States, we have enough car seats on the road for every man, woman and child - with enough seats available to hold the entire population of continental Europe." - Paul Cherington, former Assisstant Secretary of Transportation

To make this quote all the more depressing, I found it published in The Innerspace Project by Jeff Berner in 1972!
As of 2004:

Another old statistic that has probably gotten worse rather than become irrelevant:

According to a traffic study made here [in New York City] in 1907, horse-drawn vehicles moved at an average speed of 11.5 miles an hour. (In 1966, during the daytime, automobiles crawled through Manhattan's central business district at an average speed of 8.5 miles an hour.)
from The Epic of New York City: A Narrative History by Edward Robb Ellis

199 Million Drivers in America
237 Million Motor Vehicles
Motor vehicles does include motorcycles and scooters, which, if Hummers are the alternative, I will whole-heartedly support.