Density doesn't need to mean high rises. In beautiful cities such as Copenhagen and Montreal most of the housing is 3-4 stories tall with 50-60 people per acre. Such places are the opposite of sprawl. These cities have a wonderfully high quality of life and are home to healthy, active populations. Modern sprawl forces us to waste time driving which consumes more energy while generally reducing levels of physical fitness. A comfortable density is in fact more "green" than driving your hybrid in all directions to and from your compost-field-surrounded "green" home thats miles from anywhere.