Comparison of life cycle environmental performance of public road transport modes in metropolitan regions

Abstract

A comparative life cycle energy and environmental inventory has been developed for public road transport modes in metropolitan regions in India. The environmental performance of public bus transport (PBT) and intermediate public transport (IPT) modes, viz. taxi and auto-rickshaw, in Mumbai Metropolitan Region has been assessed and compared at off-peak, average and peak levels of vehicle occupancy. Moreover, the environmental performance of vehicles adhering to Bharat Stage (BS) emission norms has been assessed. The inventory captures both vehicle operation (tail-pipe emissions) and non-operation components (e.g. vehicle manufacturing, vehicle maintenance and fuel production). GaBi 6.5 has been used to assess the environmental impact in terms of global warming, acidification, eutrophication, photochemical ozone creation, abiotic depletion potential and primary energy demand. The functional unit of the study was defined as passenger kilometre travelled in 15 years, the service lifetime of the vehicle. The results show that tail-pipe emissions dominate the life cycle environmental impact of PBT (75% of 17.2 g CO2-eq/PKT), taxi (78% of 85 g CO2-eq/PKT) and auto-rickshaw (78% of 78 g CO2-eq/PKT). However, in case of vehicles adhering to BS-VI stringent emission norms, vehicle non-operation components dominate the life cycle environmental impact of public road transport modes. Therefore, vehicle non-operation components should be considered while addressing the environmental performance of public road transport modes. For all three occupancy levels, PBT is environment-friendly compared to IPT modes. However, the break-even point assessment highlights that the bus services should be operated with at least 11 passengers to make its global warming potential equivalent to IPT modes. In case of shared services of the taxi and auto-rickshaw, this equivalency increases to 23 and 29 passengers, respectively. Eventually, this study provides the benchmark that can lead regional transport planners to more informed and prioritized mitigation measures for improving the environmental footprint of public transportation in metropolitan regions in India.