Who will be the 300 millionth ?

America’s population is on track to hit 300 million on Tuesday morning, and it’s causing a stir among environmentalists.

People in the United States are consuming more than ever — more food, more energy, more natural resources. Open spaces are shrinking and traffic in many areas is dreadful.

But some experts argue that population growth only partly explains America’s growing consumption. Just as important, they say, is where people live, what they drive and how far they travel to work.

“Because the U.S. has become a suburban nation, sprawl has become the most predominant form of land use,” said Vicky Markham, director of the Center for Environment and Population, an advocacy group. “Sprawl is, by definition, more spread out. That of course requires more vehicles and more vehicle miles traveled.”

America still has a lot of wide-open spaces, with about 87 people per square mile, compared with about 600 people per square mile in United Kingdom and almost 900 people per square mile in Japan.