Urban Form and Sustainability: Modelling Evidences From the Empirical Case Study of Rome

It is widely accepted that a connection exists between the shape, size and density of an urban area and its sustainability. However, consensus is lacking about the extent and characteristics of this relationship. Certain urban forms appear to be more sustainable in some respects, for example in reducing travel, but unfavourable in other aspects, as the environmental quality or social inequalities; furthermore, some forms may be sustainable locally, but not at the city wide scale (Burton et al. 2013). A number of empirical studies dealing with the influence of urban form on sustainability has not been conclusive and comes out with mixed outcomes. In order to provide empirical insights to this debate, this study investigates the relation between urban form and sustainability in terms of economic, social and environmental characteristics of the transport-land use integrated system, by comparing three different urban forms: compact, TOD and sprawl. The main research question is: does urban form, in terms of density and distribution of activities, impact the sustainability levels of urban areas? To give an answer to this question, the paper proposes a methodology for assessing urban forms, based on a system of Land-Use and Transport Interactions (LUTI) models. This has been designed and applied able to simulate the behaviour of both dwellers and transport users and how they react to changing conditions. A system of indicators has been then set up to systematically test and compare three urban scenarios, which differ in terms of density and distribution of activities and to assess to what extent different urban structures achieve or not sustainability in terms of economic, environmental and social impacts. More details are provided in the methodological section. © AET 2014 and contributors 2 This study presents some innovations points with regard to the existing literature. First, while already existing studies mainly focus of the assessment on a single urban form (with the exception of some more recent studies, Echenique et al., 2012), in this study we compare three urban structures. An additional difference with present literature is that most studies focus on small scale and local factors influencing travel behaviour and its consequence on sustainability level, while in this research we analyse the interaction between urban form and sustainable travel behaviour at the city wide scale. Finally, another novelty regards a specific application of utility based models, which are usually used for simulate the LUT system performance in terms of transport network speed or congestion. In this study we instead integrate them in a scenario analysis and in particular addressing sustainability and equity issues as managing the side effects of growth such as sprawl, congestion, housing affordability, pollution, energy consumption and loss of open spaces. In this way, we do not examine the effect of urban form only by parameter of travel (distance, time, frequency), but we propose a more complete sustainability assessments. Nevertheless, it is important to stress that in this study we do not take into account health and well-being aspects of sustainability, putting this focus off at future steps of the research. The paper is organized as follows. In Section 2 we refer to the existing literature and to the debate on the relations between urban form and sustainability. Section 3 describes the research design and in particular the system of models and the assessment indicators system. In Section 4 we discuss the results of the application to the empirical case study of Rome. Conclusions are drawn in Section 5.