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Rijden in cirkels? Modellering van de impact van veranderingen in de vraag in functie van circulaire automobiliteit

Year: 2024
Type: dissertation
Abstract: The aim of this thesis is to understand the impact of a transition to a circular economy for car mobility, focussing on behavioural changes consistent with circular economy (CE) strategies. The focus on behavioural changes exposes the potential of demand-side strategies, i.e., those that focus on changing the incentives and barriers for consumers and how to fulfil their demand for mobility. Much of the CE literature is focussed on how to improve technologies so that goods can be produced and used using as few resources as possible. By focussing instead on behavioural changes, we shift the onus from the technological and supply side, from producers and engineers, to policymakers and social scientists and the (dis)incentives and nudges that can also help deliver a CE. The first aim of this thesis was to understand the methods and limitations of existing car-sharing impact studies, and to make recommendations for future car-sharing impact studies. We reviewed 25 car-sharing impact studies that estimated the effect of car-sharing on car ownership or car use, assessing their methods based on: the strength of the causal inference, the extent of uncertainty and sensitivity analysis, and whether environmental benefits were evident based on evidence produced. The review of these methods drew on literature from the fields of impact evaluation and life cycle assessment (LCA). A key finding was the limited use of quasi-experimental methods to estimate impacts, with many studies instead relying on other methods that are prone to a range of biases. As well as using quasi-experimental methods, uncertainty and sensitivity analysis could be used to improve the rigour of future impact studies. We also found that environmental impacts were rarely the focus of studies, and that environmental benefits were sometimes hypothesised based on proxy indicators. Confidence in the environmental benefits of car-sharing could be improved if methods such as LCA were used as well. Building on these recommendations, the aim in Chapter 3 was to estimate the impacts of car-sharing on car use in Belgium using quasi-experimental methods. To this end, car-sharing users and non-users in Flanders and Brussels were surveyed on their mobility behaviour and, for non-users, their interest in car-sharing. Two types of bias were the main focus in this method: first, reverse causality, where the impact of car-sharing on car ownership can work both ways; and second, selection bias, where car-sharing users choose to join car-sharing based on their own characteristics, meaning they may be systematically different to non-users. To overcome selection bias, we combined propensity score matching with regression analysis to estimate the impact of car-sharing on car use using data from both car-sharing users and non-users. This method controls for the systematic differences between these two groups and should reduce bias. Reverse causality was handled by testing the sensitivity to the effect of car-sharing on car-ownership. The results showed that car-sharing could reduce car use, but the results were very uncertain, significantly depending on the car-ownership effect. This novel method could be used in future studies to estimate the impact of car-sharing on car use. In Chapter 4, we broadened the analysis to look at other demand-side CE strategies in addition to car-sharing: the shift from larger to smaller cars, and the lifetime extension of existing cars. This chapter had three aims: to estimate the long-term potential of demand-side CE strategies to reduce global warming potential (GWP) and resource extraction of private car mobility in Belgium; to understand the mechanisms of these impacts and identify unintended consequences; and to identify monitoring indicators of the circular transition in car mobility. To achieve this, we built a dynamic stock-flow model of the Belgian car fleet, integrating material flow analysis (MFA) and life cycle assessment (LCA) to estimate the life cycle impacts on GWP and on the extraction of aluminium and lithium. The demand side CE strategies were modelled over 40 years to assess how and by how much the stocks and flows of cars and the impacts were affected. The evidence of this chapter suggests that these demand-side strategies can be effective, for example by reducing life cycle GWP impacts by 13\%. Downsizing from larger to smaller cars was the most effective strategy, followed by car-sharing. The effects of lifetime extension varied significantly, with lifetime extension causing both higher and lower annual impacts during the time horizon, these results highlighting the benefit of dynamic modelling. The final contribution of this chapter was the identification of leading indicators that could be used to monitor not just the strategies explored, but also the transition to more circular mobility. The aims of Chapter 5 were twofold: to estimate the long-term potential of car-sharing to reduce environmental impacts given uncertain behaviour; and to identify the most important firm choices and consumer behaviours to reduce environmental impacts. We adapted the dynamic stock-flow model used in Chapter 4 to investigate how changes to car ownership and car use amongst car-sharing users, and changes to a shared car's use-intensity, fuel type, and service lifetime affect GWP and lithium extraction over 30 years. Based on the results, car-sharing could help to reduce impacts on GWP and lithium extraction, but there is significant uncertainty around how much. For GWP, the results showed that car-sharing is very likely to reduce life-cycle GHG emissions, but there is a possibility that car-sharing could lead to an increase in territorial GHG emissions during the use phase, since car-sharing can cause an increase in the use of more fuel inefficient cars for some users. Using global sensitivity analysis, we found that the results are most sensitive to changes in user behaviour, particularly in the proportion of users who reduced their car-ownership because of car-sharing. Results were less sensitive to firm choices, with only the use-intensity of shared cars affecting results to any significant extent. This chapter highlights that if policymakers are to pursue car-sharing as part of a CE transition in mobility, then they should focus on shifting users away from ownership, since reduced territorial emissions are not guaranteed. To summarise, this thesis contributes to both research and policy, by developing new methods to help estimate impacts, by highlighting the potential of demand-side CE strategies to reduce impacts and their unintended consequences, and by describing how the transition to a CE for mobility should be monitored. Future research could focus on two aspects: first, repeating the static analysis of car-sharing's effect on car use, tracking changes over time; and second, integrating economic or other models with the dynamic stock-flow model so that specific policies can be assessed.
Source: Lirias
Language: English
Open Access status: green
OpenAlex ID: W7052504327
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