At less than 20mpg, American cars average a lower fuel economy than any other country in the world. Combine that with the fact that we also drive further each day than everyone else on the planet and the carbon dioxide emissions get pretty scary. Here’s a bit from an interesting article on American driving habits:

Americans represent 5% of the world’s population but drive almost a third of its cars, which in turn account for nearly half the carbon dioxide pumped out of exhaust pipes into the atmosphere each year, according to a report…

With suburban sprawl far outpacing the growth of public transport networks, Americans are commuting more each year, shopping more, and driving further to the shops each time. Between 1990 and 2001 the number of miles travelled on American shopping trips rose by 40%.