Impact of electric vehicle downsizing on shared mobility considering externalities

The global trend of vehicle electrification has led to the rise of affordable, compact models. This study examines the impact of vehicle downsizing on car-sharing systems using agent-based simulations. We present a vehicle dispatching model that matches vehicles to demand based on size and ride-splitting rules. To explore how vehicle size affects traffic operations, we employ the macroscopic fundamental diagram. We focus on two-seat vehicles as representatives of small models and the shared automated electric vehicle system as a prototype for effective car-sharing. Utilizing the Manhattan network, we design scenarios to assess the performance of dispatching models, optimal fleet sizes, ride-splitting effects, and the influence of compact vehicles on customer experience and social benefits. Results show that substituting standard five-seat vehicles with 80% two-seat vehicles markedly improves performance across various metrics, highlighting the significant potential of small-sized vehicles in future car-sharing systems. Sensitivity analysis confirm the robustness of our findings.