Traffic noise harms public health, but the specific mechanisms are not fully understood. To understand how traffic noise at different sound pressure levels (SPLs) affects psychophysiological responses, this study examined five SPLs of traffic noise: 40, 45, 50, 55, and 60 dB. 38 young college students were recruited for Profile of Mood States (POMS) evaluations and measurements of electrocardiogram and electroencephalogram. The study found that traffic noise exposure led to a 0.95–1.64-fold increase in mood disturbance compared to no sound, with 60 dB traffic noise causing a significantly greater increase compared to other SPLs. As SPL increased, ΔLF/HF increased by 0.01–0.83, indicating heightened stress levels. Traffic noise also induced stress responses in the brain, with α power reduced by 13.08–24.15 % compared to no sound. High SPL traffic noise significantly harmed brain comfort. Compared to 40–45 dB, exposure to 50–60 dB traffic noise significantly increased α power by 28.66–85.80 % (p < 0.05). Additionally, 60 dB traffic noise increased the likelihood of supercritical brain activity by 32.49 % compared to no sound. Psychological response changes were closely related to physiological response changes. Δα power, particularly in the frontal and parietal lobes, was the strongest predictor of the increase in total mood disturbance, suggesting these lobes should be the focus of future traffic noise-brain studies. The study emphasizes the need for a comprehensive evaluation of the negative effects of traffic noise from a psychophysiological perspective, highlighting the harm of high SPLs. The findings provide valuable insights for developing indoor acoustic environment standards.