居住-就业距离对交通碳排放的影响

城市扩张过程使交通需求量增加，导致来自交通部门的碳排放量增加。紧凑型城市发展有助于减少交通需求从而降低交通部门的碳排放量。本研究基于一个问卷调查利用情景分析的方法定量探讨居住-就业距离变化对通勤碳排放量的影响，为科学规划城市格局提供理论依据。研究结果表明在居住-就业距离不超过15 km（适宜公共交通出行距离）的情景中居住-就业距离缩短21.3%，交通碳排放量减小28.2%，费用节省21.2%；在居住-就业距离不超过5 km（适宜非机动车出行距离）的情景中居住-就业距离缩短56.3%，碳排放量减小53.1%，费用节省34.6%。两种情景下不同出行方式中，公交系统对行驶里程缩短的影响最大，私家车对碳排放量减小和花费降低的影响最大。在城市扩张过程中应该力求实现功能多元化的扩张格局，城市交通体系建设应为低碳出行提供最大便利。

Significant impact of job-housing distance on carbon emissions from transport: a scenario analysis

Transport demand is increasing with the process of urban sprawling, which leads to the rise of carbon emissions from the transportation sector. Compact urban development helps to reduce transport demand, which is critical to reduce carbon emissions from transport. However, urban sprawling in Beijing leads to increased job-housing distance, and correspondingly, to the increase of transport demand. This study quantified the influence of job-housing distance on carbon emissions based on a survey and tried to explore the impact of compact urban development on emission mitigation through scenario analysis. Two adjusted scenarios were considered in this study. In scenario-1, the job-housing distance remained within 15 km, which was suitable for the use of a public transport system; in scenario-2, the job-housing distance was within 5 km, which was suitable for active traveling modes. Results showed that in scenario-1, job-housing distance decreased by 21.3%, while the vehicle-kilometers traveled (VKT), the amount of carbon emissions and the cost of commuting declined by 12.4%, 28.2% and 21.2% respectively; in scenario-2, job-housing distance decreased by 56.3%, and these indices dropped 48.9%, 56.3% and 34.6% separately. Different traveling modes had different characteristics. Public transport system took up over 65% of the total VKT under present conditions; it contributed 67.2% of the reduced VKT value in scenario-1 compared with present conditions, and 70.5% in scenario-2. In comparison, VKT by private car account for 28.7% of total VKT, and had few impacts on the VKT variations in the two scenarios. The public transport system had little influence on reducing carbon emissions and commuting expenses, while private cars played an important role in two scenarios. The contribution of the public system to total carbon emissions was no more than 10% in present conditions, and its influence on emission mitigation and expense cuts was small in adjusted scenarios. Compared with the public system, private cars had opposite features. Their contribution to total carbon emissions was over 80% under present conditions, and in the adjusted scenarios its influence on the reduction of emissions and cost cuttings was the deepest. In scenario-1, 82.6% of emission mitigation and 86.3% of expense cuts originated from private cars, while in scenario-2, private cars contributed to 90.3% of emission mitigation and 101.0% of cost cuts. In the process of urban development, it is important to shorten job-housing distance by improving the functional diversity of different urban units and building a high-efficiency public transport system. This research led to several suggestions on how to mitigate carbon emissions from the transport sector. Firstly, it is necessary to keep a job-housing balance in urban planning, in order to decrease transport demand. Secondly, public infrastructure should be friendly to active traveling modes, and can encourage more citizens to use the public transport system, which is a fundamental feature of low-carbon traveling. Thirdly, the usage of private cars has to be controlled by policies such as usage limitation, or extra fees on driving during rush hours. Finally, through environmental education, it is possible to improve people's knowledge on low-and zero-carbon traveling modes, and encourage them to do so.