Discussion of 'Methodology for Assessing the Sustainability of Metro Systems Based on Emergy Analysis' by Dezhi Li, Eddie Chi Man Hui,Xing Xu,Qiming Li

摘要

The discussed paper aims to develop an effective methodology for assessing the sustainability of metro systems by using emergy analysis. There are several issues to be further clarified in terms of emergy analysis. This discussion focuses on (1) the definition and estimation of some emergy indexes, including emergy yield ratio (EYR), ratio of waste to total yield (RWY), and metro's emergy sustainability index (MESI); and (2) the calculation period adopted in the discussed paper. Moreover, a composite index termed the emergy cost-benefit ratio (EmCBR) is proposed for better understanding the feasibility of metro systems.