| Summary: | Transport contributes around 25% of greenhouse gas emissions, responsible for climate change. The present work explores the potential to reduce these emissions through enhanced use of excess capacity in the urban transport system. For example, average occupancy in the UK is only 1.4 persons per vehicle for cars, therefore considerable excess capacity exists in these vehicles. Capacity and sustainability have largely been examined in isolation in various academic literatures. Existing research on capacity has focused on engineered specifications of transport infrastructure, rather than examining the potential to make more efficient use of infrastructure. Research on the sharing economy and transport and the potential of increasing vehicle occupancy for fuel savings is emerging, beginning to address some aspects of capacity and sustainability. The present work contributes to and extends these emerging areas of research. The objective of this research is to explore the potential for enhanced use of current and future excess capacity within an urban transport system in order to reduce CO2 emissions. This objective addresses the identified knowledge gap and practical challenges of reducing transport emissions. The research draws on theoretical approaches from a range of disciplines, including economics, engineering and sociological perspectives, integrating these through a socio-technical systems approach. The work also draws on the sustainable mobilities perspectives to provide a holistic examination of the urban transport system. The empirical work focuses on a case study of Greater Manchester (GM), which represents an archetypal large urban area in the UK. A behavioural study incorporates a survey of 500 residents of GM, in order to understand how people use their transport capacity. The survey results are then developed into a series of scenarios: 1 A: Shared Automobility, 1 B: Intelligent Automobility, 2: Public Mobility and 3: Flexi-mobility. These scenarios are then modelled using a traffic network model. Policy recommendations are made throughout this thesis and discussed with stakeholders through interviews to understand the practicality, acceptability and barriers to implementation. The present work shows that approximately 56% of vehicle capacity is found to be excess in GM, however the survey identified a number of potential areas for making enhanced use of this excess capacity. 53% of participants were found to be willing to car share and participants showed flexibility in their travel behaviour and mode choices. Transport modelling of the scenarios shows that Scenario 1 A: Shared Automobility has the greatest potential for reducing emissions, with a reduction of 35% in CO2 emissions in 2035 compared to Business as Usual. However, stakeholders identified practical and political barriers to increased sharing, and suggested that other policy measures, such as re-regulation of transport, have greater potential for influencing the sustainability of urban transport. This thesis shows that there is a significant amount of transport excess capacity in GM and that enhanced use of this capacity could contribute to reductions in CO2 emissions. These findings are applicable to areas with similar transport systems to that of GM, particularly in the UK. The framework developed in this thesis could be applied to other urban transport systems to assess the emission reductions potential of making enhanced use of excess capacity in urban transport.
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