Evaluating the emission reduction potential of first underground metro rail in Mumbai, India through a modal shift and energy use perspective

Abstract The increasing environmental and health burdens caused by road-based transportation in urban India make it imperative to shift toward sustainable mobility solutions. Metro rail systems offer significant potential for reducing greenhouse gas and air pollutant emissions. This study evaluates the emission reduction potential of the first underground metro rail system in Mumbai, India. The analysis estimates the emissions avoided from reduced on-road vehicle usage and compares them with the emissions generated by metro operations powered by a combination of solar and grid electricity. The study considers five key pollutants, namely carbon dioxide (CO 2 ), carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NO x ), and particulate matter (PM), to assess both climate and local air quality impacts. A mode shift analysis was conducted based on projected ridership of 1.56 million daily passengers and modal share assumptions derived from recent travel behavior studies. Vehicle categories, fuel types, occupancy, and vintage distribution were considered in estimating avoided emissions. Emissions from metro operations were calculated using electricity demand for traction and auxiliary purposes. The results show a net reduction of 155 tonnes of CO 2 per day, along with daily savings of 3871 kg of CO, 2526 kg of HC, 133 kg of NO x , and 82 kg of PM. The greatest emission reductions were achieved by shifting vehicles from two-wheelers (12–48%), auto-rickshaws (19–47%), and taxis (5–34%), owing to their high emission intensity, while buses (9–14%) and cars (4–29%) contributed moderately. A scenario analysis was performed to evaluate the sensitivity of net emission savings to changes in modal shift composition, energy source (solar vs. grid), and ridership levels. Scenario analysis revealed that a greater shift from private vehicles and increased reliance on renewable electricity can further enhance mitigation. The study underscores the importance of renewable energy and strategic modal shift planning to maximize the environmental benefits of the metro rail system.