Assessment of Emissions and Their Impacts from Bus Operations Under Varying Traffic Conditions and Their Impact: Literature Review

Abstract

The transportation sector is a major contributor to urban pollution, and public transportation systems are widely promoted to reduce urban pollution levels. This review assessed emissions across bus operating phases, measurement methods, and mitigation strategies. A structured literature review was conducted, integrating 109 peer-reviewed publications from 2005 to 2025, using major academic databases, including Scopus, Web of Science, and Google Scholar. This study revealed that vehicle-related emissions can lead to respiratory and cardiovascular health effects and contribute to environmental issues, such as smog, acid rain, and ecological disturbances. Vehicle design parameters, operating phases, driver behaviour, and transport infrastructure influence the emission levels. Electric vehicles are the most environmentally friendly option owing to zero tailpipe emissions, whereas in conventional vehicles, acceleration and idling are the most critical emission phases, with peaks at the start of acceleration and end of idling. The absence of dedicated bus lanes at curb-side stops can increase peak-hour emission factors for CO, PM2.5 and PM10 by over 50%, and at bus bays, increases of 37.2%, 47.8%, and 47.6%, respectively, highlighting the role of transport infrastructure. Emissions are typically estimated using real-world measurements or modelling approaches, with the latter being more widely applied. Effective emission reduction requires integrated mitigation strategies that combine technological advancements with policy interventions focusing on driver behaviour and critical operating phases.