Life cycle environmental assessment of elevated metro rail system: insights from the Mumbai Metropolitan Region for sustainable urban mobility

Metro rail systems have recently become an essential transportation policy choice for urban commuting in many emerging countries, including India. However, their life cycle environmental impacts, particularly energy and emissions during the construction and operation phase, raise critical considerations. The broader perspective on the environmental trade-offs involved in transitioning from traditional to modern rail systems should be assessed. This study assessed the life cycle environmental performance of elevated metro rail transit (MRT) in the Mumbai Metropolitan Region, India. The system boundary includes the construction of a viaduct, elevated stations, and a power supply system. Additionally, it encompasses the construction and maintenance of slab track and metro coaches. The operation phase includes the traction electricity needed to run trains and the auxiliary electricity required to operate elevated stations. The functional unit of this study is per track km (TKM) and per passenger km travelled (PKT) in 30 years, the service life of the metro train. The results show that the construction of slab track constitutes the largest portion of the global warming potential impact of MRT infrastructure (59% of 3200 t CO2 eq/TKM), nearly half of which comes from the rails. The traction electricity demand dominates the life cycle impact of the MRT (65% of 19.2 g CO2 eq/PKT), whereas auxiliary electricity consumption contributed 30% to all impact categories. The environmental impact of the modern MRT infrastructure was compared with that of conventional infrastructure for the Mumbai Suburban Railway (MSR). The longer service life of the slab track and fastenings makes the life cycle impact of the MRT competitive with the MSR. The combination of utilizing renewable energy and increased usage will make the MRT systems more competitive in the realm of sustainable urban mobility. The MRT system utilizing renewable electricity and endorsing high ridership will improve the environmental footprint of urban mobility.