The environmentalist cliche of the late 1990's. It is a real problem, and it's the particular problem that's getting a lot of press. Probably, because the mainstream can really see it (as opposed to the rain forests). This problem is worsened by the exclusive use of roads in city design, ignoring other forms of transportation (railroads, subways, or sidewalks). If you can't get lunch without getting in a car, you know this problem.