<p>This study examines the environmental and social implications of replacing diesel buses with battery-electric buses in Belo Horizonte, Brazil, through a clearly defined research question and an analytical framework grounded in emission-accounting methodology and social impact indicators. Environmentally, the avoided emissions were estimated using GHG Protocol-based factors and include uncertainty ranges to account for variability in fuel composition, electricity-grid intensity, and annual fleet mileage. The results indicate that full electrification of the municipal fleet could avoid 125,414 t of CO₂ emissions per year, with sensitivity analysis showing a ± 10% variation depending on operational and energy-mix assumptions. Additionally, 7.8 t of CH₄ and 7.4 t of N₂O emissions could be avoided annually. Social impacts are assessed using secondary indicators related to air quality exposure, noise reduction, accessibility, and mobility equity, highlighting measurable co-benefits for public health and urban inclusion. By integrating environmental and social dimensions, the study contributes empirical evidence to ongoing debates on sustainable urban transport transitions in metropolitan contexts.</p> Graphical abstract <p></p>