Computer models provide considerable assistance to urban planners. In particular, they provide a user-friendly minimum cost mechanism for investigating the impacts of policy. One such policy relates to increased urban densities. The rapid spread of low density suburbs in Australia is often seen as increasing individual travel and emissions. Yet the development of self-contained cities in outer suburban areas may enable people to work, live and recreate locally, thereby decreasing travel and reducing some of the concerns about outward growth. This paper therefore presents two computer model studies into different urban forms relating to sustainable development and the reduction of greenhouse emissions.