Research on the Combined Effects of Plant Odor and Traffic Noise on Crowd Behaviors in Urban Environments

Traffic noise is a typical negative sound source in urban environments with impacts on crowd behaviors. To explore the combined effects of auditory–olfactory interaction environments on crowd behaviors, this study conducted a covert behavioral observation experiment on a typical urban street uniformly planted with lilacs (Syringa spp.) to investigate the combined effects of plant odor and traffic noise on crowd path and crowd speed. The results showed that: 1) for crowd path, when the sound pressure level (SPL) was high, the path ranges and their mean values under different odor concentrations all showed a tendency to be farther away from the sound source than when it was low; the mean values of path ranges gradually moved towards the odor source as the odor went from none to strong, which was more significant at high SPL, with a maximum longitudinal movement of about 0.3 m. 2) For crowd speed, its mean values gradually slowed down from 1.24 m/s at high SPL as the odor went from none to strong and then stabilized at 1.18 m/s; however, those at low SPL were almost unaffected. This research puts forward new ideas to alleviate the negative impacts of traffic noise, and the study results can provide guiding significance for the improvement of the evaluation system of urban landscape quality and the optimization of urban design mode.