it's not just emissions or milage... it's how much you drive. You can have the biggest gas hog in the world, but if you ride your bike 85% of the time seems to me it would be better than driving your little car to the 7-eleven 3 blocks away (in addition to work 5 miles away and the gym 2 mile away)
Oh, wait, that just might help with the obesity problem america is facing...