Methodology for assessing the sustainability of metro systems based on emergy analysis

The sustainability of a metro system is important not only to itself but also to local socioeconomic development. However, very few methodologies can be found for assessing the sustainability of metro systems, especially on the basis of emergy analysis. Demonstrating many advantages in sustainability assessment, emergy analysis has been utilized in assessing the sustainability of many objects including regions, industries, products, and projects. A methodology for assessing the sustainability of metro systems on the basis of emergy analysis is thus proposed in this paper. The proposed methodology aggregates three emergy indexes, namely, emergy yield ratio (EYR), environmental loading ratio (ELR), and the ratio of waste to total yield (RWY). Each of them has a specific sustainability meaning, whereas the proposed metro's emergy sustainability index (MESI) is equal to the ratio of EYR divided by the product of ELR and RWY. Then, the first stage of Nanjing Metro's Line one is studied as a case. It is believed that the proposed methodology is easily replicable and useful for design optimization of metro systems in the early stage.