Mechanisms for the Low-Carbon Transition of Public Transport Energy Systems: Decoupling Emissions and Energy Consumption in Inner Mongolia and the Path to Three-Chain Synergy

To achieve deep decarbonization in the transportation sector, this study employs life cycle assessment (LCA) and the GREET model to construct baseline and low-carbon scenarios. It simulates the evolution of emissions and energy consumption within Inner Mongolia’s public transportation energy system (including diesel buses (DBs), electric buses (EBs), and hydrogen fuel cell buses (HFCBs)) from 2022 to 2035, while exploring synergistic pathways for its low-carbon transition. Results reveal that under the baseline scenario, reliance on industrial by-product hydrogen causes fuel cell bus emissions to increase by 3.64% in 2025 compared to 2022, with system energy savings below 10%, and decarbonization potential will be constrained by scale limitations and storage/transportation losses in cold regions. Under the low-carbon scenario, deep grid decarbonization, vehicle structure optimization, and green hydrogen integration reduced system emissions and energy consumption by 66.86% and 40.44%, respectively, compared to 2022. The study identifies a 15% green hydrogen penetration rate as the critical threshold for resource misallocation and confirms grid decarbonization as the top-priority policy tool, yielding marginal benefits 1.43 times greater than standalone hydrogen policies. This study underscores the importance of multipolicy coordination and ‘technology-supply chain’ synergy, particularly highlighting the critical threshold of green hydrogen penetration and the primacy of grid decarbonization, offering insights for similar coal-dominated, cold-region transportation energy transitions.