There are now over one billion automobiles on the road worldwide. An explosion in the auto markets in China and India ensures that number will increase, with China supplanting the United States as the world's largest car market. It's fair to say humanity has a love affair with the car, but it's a love-hate relationship. Cars are at once convenience, art, and menace. People write songs about their vehicles, put them in museums, race them, and wrap their identities up in them. About 15% of carbon dioxide emissions from the burning of fossil fuels comes from cars. Traffic fatality estimates vary from half a million per year to more than double that. Gathered here are images of the automobile in many forms, and our relationship to and dependence on our cars. This is the second in an occasional Big Picture series on transportation, following Pedal power earlier this year. -- Lane Turner ( 40 photos total