Dramatic Population Growth Presents Opportunity to Reshape America's Urban Environment

"It is unlikely that city building on the scale to be seen through 2050 will happen ever again," says Penalosa. "Cities are a means to a way of life: the kind of urban structures created over the next few decades will have profound consequences in terms of quality of life, environmental sustainability, economic well-being, and even happiness and the civilization for hundreds of years to come. If we consider the influence American cities will exert on the rest of the world, the way they are built will determine, as well, much of the world’s sustainability and well-being."

Can high-density infill or traditional neighborhood development provide the model? "I don’t think so," he argues. "I believe a different urban model is possible: a dense city with a large percentage of buildings facing pedestrian-and-bicycle-only promenades or greenways."