I drive a 2004 Ford Mustang with a little "6 Banger" giving me the illusion of driving a sports car. Using the Carbon Footprint Calculator my annual carbon footprint driving the Mustang at 15,000 miles is 6.99 tons. Having used (according to my SoCal Edison bill) 323kWh of electricity during the last billing period, I could be charged for an additional .09 tons of carbon. Looking at the footprint generating from a month of using Metro Rail to go to and from Long Beach to downtown Los Angeles the footprint adds, well it adds almost nothing.
Now I probably use a lot less electricity than the average person, so my electrical carbon load is not too bad. My Mustang is a pig, but not as big a pig as say, an Escalade, which would be almost twice as dirty as the Mustang. Versus a Prius, which would produce 3.2 tons of carbon, I don't fare so well.
Anyway you look at it, it is a lot of carbon, all finding its way into the environment, ozone, oceans - anyplace carbon can fly or die into the planet.