Eight years ago, Richard Forman, a landscape ecologist at Harvard University, had what he describes as “a little epiphany.” Forman had gained renown with his book Land Mosaics: The Ecology of Landscapes and Regions and was subsequently invited to join a national council on the impact of the U.S. transportation network on ecology. The council focused largely on climate, but Forman realized that he and his colleagues were missing the point. “It occurred to me that the most conspicuous feature of the landscape was the least known”—roads.