Drivers and exposure dynamics of transport-related noise pollution at bus stop microenvironments

Urban public transport is a critical source of environmental acoustic pollution, yet the specific drivers of its disruptive and highly transient pollution intensity at bus stops remain poorly quantified. This study investigated the determinants of short-term acoustic pollution fluctuation, defined as the difference between the L₁₀ (peak) and L₅₀ (median) sound levels (ΔNoise), at 100 bus stations in Isfahan. Using a stratified sampling design, we collected continuous acoustic measurements alongside contextual data on traffic and passenger activity. A generalized additive model (R² = 0.837) was employed to analyze the non-linear effects of predictors on ΔNoise as an indicator of fluctuating pollution intensity. The results revealed a highly impulsive acoustic pollution environment, with a mean ΔNoise of 6.30 dB. Motorcycle count was the dominant predictor, exhibiting a strong, linear positive relationship (edf ≈ 1.00, F = 200.87, p < 0.001). Vehicle speed showed a significant non-linear effect (edf = 3.31, p < 0.001), with ΔNoise peaking at intermediate speeds (~ 35 km/h). Scenario analysis demonstrated that a 60% reduction in motorcycle flow yielded the largest pollution mitigation, reducing ΔNoise by a mean of 4.31 dB. In contrast, reducing passenger density alone had a minimal effect (0.605-dB reduction). These findings show that acoustic pollution fluctuation at bus stops is primarily governed by motorcycle traffic and vehicular speed patterns. They provide a critical evidence base for targeted traffic-source control strategies rather than generalized pollution management measures.