First, a surprising statistic about per capita car ownership. The USA doesn’t even rank in the top five!
First, a non-surprising statistic about per capita vehicle ownership. The USA ranks at the top!

(Source)
(Old Source – This data set was silly since it just measured cars and not motor vehicles per Bob’s comment below.)
Second, Americans spent about 52.2 cents per mile on their personal vehicles in 2007 after adding all the costs of ownership such as purchase price, insurance, maintenance, and gas. At an average usage of 15,000 miles per year, that works out to $7,800 per year per car.
Let’s compare that to the cost of public transit. It’s about 15 miles of BART rail from Civic Center to Richmond. At a fare of $3.80 that works out to 25.3 cents per mile, half that of a vehicle.
Third, Americans hold an average of $8,000 in credit card debt per household.
“Stop right now,” you say. “This is nothing but a silly conjecture! That credit card debt isn’t directly related to personal vehicle expenditure. And, your cute little Bay Area public transit system doesn’t exist in most other US cities.”
“True and true,” I’ll respond. “But, chopping transportation spending in HALF would significantly reduce a major household expense for many Americans. And, if we start investing NOW in smart public transit in the United States, we can reduce these significant (and quickly rising) expenses in the near future.”
Hmm. Public transit is good for the environment AND for the economy? And it decreases our reliance on foreign oil?
EXTRA CREDIT: This is a very well written post on calculating your actual per mile vehicle expenditure.