The world may be headed to two billion vehicles this century, thanks to the burgeoning love affair between the Chinese and the automobile. But consider this: where will all those cars park?

If urban planners are right, finding parking for all those vehicles might be no problem. City gurus estimate there are eight parking spots for every vehicle in the U.S. today. Given a U.S. fleet of 250 million vehicles, that means America already boasts some two billion parking spots—an area roughly the size of Massachusetts.

But according to the first nationwide count of parking spots, conducted by civil engineers from the University of California, Berkeley, last July, that might be a bit much, which is good news for the environment. It's more likely there are only three parking spaces for every car and truck in the U.S., or some 800 million spots to choose from.

Estimating the environmental cost of all that parking reveals that parking alone adds 10 percent to the CO2 emissions of your average automobile. And the amount of soot added to the atmosphere as a result of all our cars nearly doubles. That's thanks to all that asphalt and concrete and the emissions that go along with making it.

And then there are the millions of kilometers of roads in the U.S. to think about… In short, there's no such thing as free parking.

—David Biello