Long-term urban railway network expansion and pollutant emissions: Methodological approach and insights for sustainable transportation policies

Urban transportation is a major challenge in many cities worldwide and railway systems are often considered as an alternative to solve mobility and air pollution problems. However, such systems are capital-intensive, and their implementation often extends over several years, particularly in developing countries. This paper proposes a methodological approach to assess the impact of long-term urban railway network expansion on pollutant emissions applied to the Metropolitan Region of São Paulo (MRSP) in Brazil. The proposed approach consists of seven steps: define the trips of interest in a database derived from an OD survey; estimate the trip matrix in a baseline scenario and a future scenario considering the expansion of the rail network; determine the trip attributes in both scenarios; calculate the modal choice based on a Logit model; determine the number of trips per mode; estimate vehicle emissions using the bottom-up methodology; and compare the emissions between scenarios. The results of the proposed railway network would lead to a substantial increase in railway ridership between the base scenario of 2017 and the future scenario of 2030, reducing the choices for automobiles by 41%. Nonetheless, the decrease in vehicular emissions would be modest, primarily attributed to reductions in short-distance trips, resulting in estimated reductions of 0.25% for PM, 1.17% for NOx, and 3.93% for CO emissions. These findings underscore the importance of assessing the potential benefits of railway expansion with tools that consider multiple data sources and models, and the need for integrated policies to achieve sustainable urban transportation systems.