To actively promote the implementation of the national dual-carbon goal strategy, studying regional railway carbon emissions and the carbon-reduction benefits of substituting different modes of transport including road transport based on a full-life-cycle perspective, is one of the key issues for achieving carbon peaking and neutrality. This paper uses a full-life-cycle approach to calculate carbon emissions from the planning-design, material production, construction, and operation-maintenance stages of railway project, while considering energy-saving, carbon reduction, and greening carbon sequestration measures. The Beijing-Xiong'an Intercity Railway is selected as a typical case to analyze and calculate the carbon emissions of a single project. Based on total social travel data in Beijing from 2013 to 2024, and using elasticity coefficients, linear regression, and travel-characteristic analysis, regional railway passenger volumes for the planning years 2030 and 2035 are predicted. According to the development plan of Beijing's railway network, the total carbon emissions of planned railway projects in the region are estimated. Combined with projected passenger volumes in the planning years, the carbon-reduction benefits and and the economic benefits from reduced air-pollutant emissions resulting from railways substituting for different transport modes are analyzed. The results show that railway construction in the region, after generating transferred passenger volume, has yielded economic benefits of approximately 7.37 - 11.20 billion yuan from carbon reduction and reduced air-pollutant emissions, significantly enhancing the project's national-economic evaluation. For the Beijing-Xiong'an Intercity Railway, the estimated economic benefit under the carbon-reduction scenario is about 350 million yuan, which can increase the project's internal rate of return in the national economic evaluation by about 0.05%. Thus, measures including optimizing the transport structure, implementing green and low-carbon development, and establishing a dual-control system for carbon emissions are effective ways to achieving railway carbon reduction. The research findings provide reference for constructing a dual-control indicator system for railway carbon emissions and improving the national economic evaluation method for railway projects.
碳排放对环境危害很大,根据联合国政府间气候变化专门委员会(Intergovernmental Panel on Climate Change,IPCC)发布的报告[1],2019年全球交通运输部门CO2排放量为89亿t,排放占比达15%。为降低温室效应对全球环境的影响,2020年9月我国向世界正式提出“碳达峰、碳中和”目标。我国当前交通运输领域直接CO2排放约占全社会排放总量的11%,且在国家碳排放中的占比将进一步扩大。根据国家铁路行业部门联合印发《推动铁路行业低碳发展实施方案》,预测至2030年,铁路客货周转量全社会占比分别达48%和22%以上,铁路单位运输工作量综合能耗和CO2排放较2020年下降10%。铁路作为绿色骨干运输和公益性基础设施,对实现区域碳达峰、碳中和承担重要支撑作用,铁路碳排放和碳减排效益已成为亟须研究的重要课题。
目前国内外学者对铁路实现双碳目标的相关研究较为局限,袁振洲等[2-4]对碳排放研究相关文献进行了梳理和综述,基于文献计量学分析详细阐述低碳效应的研究边界和碳减排机理,并采用对数平均迪氏指数(Logarithmic Mean Divisia Index,LMDI)乘法模型研究了京津冀地区交通运输业的碳排放与其他社会经济指标的交互效应。目前关于碳排放研究可以归纳为以下3大类。第1类是基于全生命周期角度对单个铁路项目部分工点或整个系统工程碳排放进行研究分析,如Rempelos[5]对传统有砟轨道全生命周期的碳足迹进行研究;陈进杰等[6]、任南琪等[7]基于全生命周期评价理论,对铁路建设、运营、回收等阶段进行研究,通过京沪等铁路案例分析各个阶段CO2排放,综合测算减排效果较好。第2类是重点针对不同交通方式影响碳排放的因子和碳排放效率等进行研究分析,如吴雪妍等[8]以单位周转量产生的碳排放量作为不同方式的碳排放因子,构建了航空、铁路、公路等交通碳排放因子模型;Oliveira等[9]运用“自下而上”法对不同能源条件下的交通领域碳排放系数与碳排放量的测度分析;Jiang等[10]对中国交通运输业的碳排放效率进行了静态和动态分析,研究了交通运输业全要素生产率的影响因素,其中人均GDP对地区碳排放影响存在显著差异。第3类是基于影响因素分析对一定区域内交通运输行业碳达峰进行研究,如Hong等[11]通过长期能源替代规划系统(Long-range Energy Alternatives Planning System,LEAP)模型分析了韩国交通部门碳排放,预测到2050年将有效降低;Mi等[12]、Gong等[13]研究了CO2排放与人口、经济增长间影响关系,利用经济和气候综合模型研究预测我国碳达峰时间,预测到2030年前后才能实现碳达峰;焦柳丹等[14]、杨东等[15]基于可拓展的随机性环境影响评估(Stochastic Impacts by Regression on Population,Affluence,and Technology,STIRPAT)模型,分别从人口规模、经济、技术、货运周转量等维度选取影响因素,建立碳排放预测模型,并对基准、低碳、高碳不同情景下地区、国家的交通运输业碳排放情况进行预测分析;方涵潇等[16]对2022年—2035年湖南省交通运输领域碳排放量峰值进行预测分析,并提出减少社会车辆、公路货运等减排措施路径。
根据全生命周期铁路各阶段碳排放测算方法,以前期研究的京雄城际[17]作为典型案例进行分析。京雄城际正线全长92.8 km,速度标准为黄村至新机场段为250 km · h-1、新机场至雄安段为350 km · h-1,全线共设车站5座。按照全生命周期碳排放方法计算,根据铁路设计规范有关要求,桥梁、隧道、路基等主体结构使用年限为100 a,将规划设计、建材生产、施工建设阶段总能耗均摊到每年运营期,考虑光伏发电、综合能管系统及绿化碳汇等节能减排措施,结合本区域电力、建材等碳排放因子,结果表明规划设计阶段产生的碳排放占比很小,运营期年均能耗最大,约占全生命周期年均总综合能耗的75%,建材生产阶段年均能耗占比约20%,考虑节能减排以及绿化固碳等措施效果明显,年均能耗可节约12%左右。全生命周期各阶段碳排放汇总表详见表1。由表1可知:每年节能减排措施和绿化固碳措施分别减少碳排放1.020和1.238万t。
研究年度区域内涉及京港台(丰雄段)、怀兴城际铁路二期、北京至城市副中心铁路、南北地下直径线、北京客运北环铁路、北京客运西环铁路等客运项目,相关项目涉及高铁、城际和部分普速铁路技术标准,京雄城际分2段建设,分别为250和350 km · h-1速度标准,属于区域内典型客运铁路案例。为此,以京雄项目全生命周期碳排放作为参考,根据各规划项目工程技术标准和工程量折算,对规划年度地区铁路项目建设、运营阶段碳排放量进行估算,结果见表4。
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