However, recent studies suggest that these developments are not as green as promised. For example, in the study by Rérat, the author discussed three criticisms of the compact city model. The first criticism was that supply and demand alignments are not feasible in some cases. What this means is that there are limits to how many people can fit into a space because of resource and design limitations. Additionally, while a high-density may be achievable, it likely will counter the demands and expectations of residents who want more privacy and more personal space. The second criticism of the compact city is that to produce highly desirable living conditions and a high quality of life, the cost of living needs to increase. Consequently, integrating desirable traits into compact cities makes the living spaces expensive, pricing out lower-income families and pushing them to the outskirts of town. This stimulates urban sprawl and places the burden of longer commutes on low-income workers, further expanding disparities in wealth and quality of life. The third criticism of the compact city is that its environmental impacts are significant. Dense populations mean waste and pollution are also dense. This concentrates the impact of communities and necessitates expensive control mechanism. Rérat is not the only researcher showing evidence that compact cities are not as sustainable as promised. The work by Westernick et al. also show that there are sustainability trade-offs found within compact city designs. Westernick et al. compared compact cities to dispersed cities to see where sustainability factors differed. The findings showed that compact cities excelled in efficient land consumption, more flexible land use patterns, cost efficiency of development and maintenance, and reduced reliance on fossil fuels and motor vehicles. In contrast, however, the sustainability disadvantages included higher vulnerability to disaster impacts, less personal space, less green space where people live, and higher environmental impact because of density. These drawbacks make compact cities less sustainable and justify the need for design improvements. The compact city, urban sprawl and automobile dependency Whether the compact city (or 'smart growth') does or can reduce problems of automobile dependency associated with urban sprawl has been fiercely contested over several decades. An influential study in 1989 by Peter Newman and Jeff Kenworthy compared 32 cities across North America, Australia, Europe and Asia. The study's methodology has been criticised but the main finding that denser cities, particularly in Asia, have lower car use