To address the limitations of existing studies regarding analytical scales and the exploration of social equity issues, an accounting–analysis–application framework is constructed to uncover the travel carbon emission patterns of urban public transportation. Based on Beijing’s smart card data, a bottom-up accounting model for travel carbon emissions at the street scale is developed. Through a three-dimensional equity system (vertical, horizontal, and spatial), the relationships between emission characteristics and socioeconomic factors are analyzed, and multi-scenario shared bicycle substitution schemes are designed to evaluate the emission reduction potential. The results show that travel carbon emissions exhibit distinct spatiotemporal patterns characterized by tidal polarization on weekdays, multi-core dispersion on holidays, and a mixed transition on rest days. Equity analysis reveals a significant phenomenon of environmental cost shifting: during peak hours, low-housing-price areas contribute half of the total travel carbon emissions, with per capita emissions 72% higher than those in high-housing-price areas, resulting in a spatial lock-in effect of low-income–high-emission and high-income–low-burden. Furthermore, shared bicycles demonstrate the optimal emission reduction effect for medium-distance trips of 2–4 km; scenario synergy can achieve an emission reduction of 4.24% and effectively promote transport environmental equity by precisely alleviating the carbon burden in peripheral communities. This study provides a systematic analytical framework and fine-grained policy references for the equitable, low-carbon transition of urban transportation.

针对现有研究在分析尺度与社会公平性议题探讨方面的局限性, 构建核算–分析–应用框架, 挖掘城市公共交通出行碳排放模式。基于北京市智能卡数据, 构建自下而上的街道尺度出行碳排放核算模型。通过三维(垂直–水平–空间)公平性体系, 解析排放特征与社会经济的关联, 并设计多情景共享单车替代方案来评估减排潜力。结果表明, 出行碳排放呈现工作日潮汐极化、节假日多核分散、休息日混合过渡的时空特征。公平性分析结果揭示显著的环境成本转嫁现象, 高峰期间低房价区贡献一半的出行碳排放, 人均排放量比高房价区高72%, 形成低收入高排放–高收入低负担的空间锁定效应; 共享单车2~4 km的中距离出行减排效果最优, 情景协同可实现4.24%的减排量, 并能通过精准地降低外围社区的碳负担, 有效地促进交通环境公平性。研究结果可为城市交通的公平、低碳转型提供系统的分析框架和精细化的政策依据。