Environmental life cycle assessment of underground metro rail: A case study in Mumbai Metropolitan Region, India

The metro rail systems have been vigorously promoted to reduce the emissions from the urban transport sector in India. However, their construction and operation are associated with high energy consumption and corresponding emissions. This study evaluated the life cycle environmental impact of the first underground metro rail transit in the Mumbai Metropolitan Region, India. The system boundary comprises the construction and maintenance of the tunnel, underground stations, slab track, power supply system, and trains. The operation phase accounts for the traction power demand for running trains and auxiliary power demand for operating the station services. GaBi 6.5 has been used to normalize the results per track-km (TKM) of the transit system and per passenger-km travelled (PKT). It has been found that the construction of underground stations is the major contributor (70% of 17,300 t CO2-eq/TKM, 52 t SO2-eq/TKM) to the life cycle impact of the infrastructure, whereas the auxiliary power demand dominates the life cycle impact (63% of 25 g CO2-eq/PKT) of the metro rail. Further results show that the door-to-door trip with a local bus service will have a 58% lower impact than a competing sedan trip. On the basis of these results, possible recommendations were proposed, such as deploying energy-efficient trains and metro stations, utilizing electricity that has met renewable goals, and endorsing high ridership. This study provides background data to quantify the environmental impacts of existing and forthcoming metro rail projects in India.