Reducing carbon emissions in the transportation sector necessitates a transformation from dominance of gasoline vehicles (GVs) to one of the new-energy vehicles

such as electric vehicles (EVs) and hydrogen fuel cell vehicles (HFCVs). However

existing studies typically fail to consider conditions during the transition

when GVs

EVs

and HFCVs coexist in significant proportions. The present work a ddresses these issues by developing a multi-objective optimization model with both economic and carbon emission criteria to coordinate the inter-dependent activities of power distribution networks and urban transportation networks. Equitable solutions between conflicting objectives are obtained by extracting compromise solutions using the augmented epsilon-constraint method. Incentives are obtained by implementing a carbon subsidy mechanism that dispenses financial reimbursements to EV and HFCV users according to their contributions to carbon emission reductions. The effectiveness of the proposed carbon subsidy mechanism for reducing the operational costs and carbon emissions of the two networks and incentivizing drivers to participate in low-carbon demand responses are verified via numerical results on an integrated IEEE 33-bus electric power system and a 13-node Nguyen-Dupuis transportation system.