The density of a neighborhood, in and of itself, turns out to be the weakest of the commonly considered "D" variables, key dimensions of the built environment that influence how — and how much — people move around.

These are among the key conclusions of "Travel and the Built Environment," a new meta-analysis by Reid Ewing and Robert Cervero of how land use patterns impact driving, walking, and transit use, published in June in the Journal of the American Planning Association.

Why should the people who help create our built environment care about the effects of buildings on transportation?

In general, in the United States, more walking is better for people and the environment, and more driving is worse — much worse.

It's a simple sequence of logic that makes "the potential to moderate travel demand by changing the built environment" what Ewing and Cervero call "the most heavily researched subject in urban planning."

First, we in the U.S. need to reduce our individual and collective carbon footprints by roughly four percent a year, year in and year out, for decades to come — starting immediately.

Second, buildings, their development, and their occupancy must be part of this long-term, very deep reduction in carbon footprint.   >>>