The American dream used to mean a good job, house in the suburbs and two-car garage. But for kids born in the 21st century, a very different reality awaits: More people will live in big cities, vehicles will drive themselves and car-sharing, not car-ownership, will be the norm.

If everything goes according to plan, anyway.

A new report released Monday by the McKinsey Center for Business and Environment declares that transportation is at a tipping point. "Megacities" such as London, Shanghai and New York City are already glutted with automobiles, but car ownership could double worldwide by 2030 if something doesn't change. And something has to change: Cars already contribute an enormous amount of pollution to our atmosphere, and that pollution is a factor in millions of early deaths every single year. Forget the American dream: Solving this problem is a global imperative.

Thankfully, we're en route.