Urban rail transit is an energy-intensive sector with substantial carbon emissions, particularly during its operational phase. Despite the rapid emergence of energy-saving technologies, the lack of systematic quantification of their carbon emission reduction efficiencies hinders comparative evaluation and informed decision-making. This study addresses this gap by developing a carbon emission calculation framework for key energy-saving technologies, incorporating an enhanced Bass diffusion model to forecast future emissions. A marginal abatement cost analysis and a Multi-Constraint Interior Point Method are further employed to formulate an optimized, multi-dimensional integrated strategy encompassing energy, vehicle, storage, and network systems. Results reveal that, in terms of carbon emission impact, the technologies rank as follows: Permanent Magnet Synchronous Motors (PMSM) traction systems, Regenerative Braking Systems (RBS), Life-Cycle Smart Environmental Control Systems (LCSMS), and various energy storage systems. While Flywheel Energy Storage (FES) technology and LCSMS initially exhibit high marginal abatement costs, these decline significantly before 2030. In contrast, Photovoltaic (PV) generation technology maintains the lowest marginal costs throughout. Investment optimization shows that the shares allocated to PV and LCSMS increase linearly, jointly approaching 85% by 2060. Consequently, investment in PV and LCSMS should be progressively scaled up to enhance carbon reduction performance. This study provides a theoretical basis for the formulation of urban rail transit policies and supports the achievement of the dual carbon strategy goals, holding significant theoretical and social value.