Optimal Bus Fleet Conversion Planning for Decarbonization: Case Study of Istanbul Metrobus

Fleet conversion using electric buses stipulates a comprehensive optimization of the fleet mix, size, and charging station decisions while minimizing the total cost of ownership and carbon dioxide emissions. Therefore, this study focuses on the optimal Electric Bus Fleet Conversion Planning in the urban transportation sector to reduce emissions under different incentives, carbon tax, retrofit bus usage, charging station type, and scheduling scenarios. It proposes a novel multi-objective mathematical model, a unique contribution of this research, to provide decision aid through this conversion process. The model minimizes the total cost of ownership and emissions to meet the Paris Agreement's targets. A case study based on the Metrobus fleet of Istanbul was performed to exemplify the usage of the model. This is the first study to simultaneously assume all the critical aspects of the fleet transition problem: electric bus purchasing, retrofit bus usage, charging infrastructure development, carbon taxes, incentives, and charge scheduling. This study's findings can help decision-makers develop optimal fleet conversion plans that balance economic and environmental objectives under different conditions. The findings imply that the fleet transition using new electric buses incurs very high capital costs, but retrofitted buses can make this transition more economically viable, offering potential economic benefits. Charge scheduling affects the sizing of and investment in charging stations. The government should provide bus purchasing and charging station incentives to support this conversion process. Besides, renewable resource usage in electricity generation plays a pivotal role in carbon dioxide emission reduction.