Traffic noise intrusion in naturally ventilated classrooms: A comparative case study from Nagpur, India using a source-path-building framework

Urban schools located along arterial roads face significant challenges from traffic-induced noise intrusion, which compromises classroom acoustic quality and student learning. This study examines how multiple architectural and site parameters influence the transmission of noise from outdoor to indoor environments through a comparative field investigation of two naturally ventilated schools in Nagpur, India. Forty unoccupied classrooms were assessed under both open- and closed-window conditions. Classrooms situated closer to the road, oriented parallel to traffic, and located below street level recorded the highest indoor noise levels (up to 70.1 dB(A)), frequently exceeding the National Building Code (NBC, 2016) guideline of 40–45 dB(A). Findings indicate that the wall opening-to-floor ratio (WOFR) alone was not found to be a reliable predictor of acoustic performance; rather, orientation, elevation, and setback interactively govern the degree of noise intrusion. Statistical modelling showed that distance and orientation were significant predictors of indoor noise levels due to traffic ( p < 0.01), with increased setback reducing exposure by approximately 0.38 dB/m and perpendicular facades lowering levels by 3–4 dB. Results provide empirical support for key components of a source–path–building framework for outdoor-to-indoor noise transmission, highlighting that no single parameter ensures acoustic comfort.