How visible street greenery moderates traffic noise to improve acoustic comfort in pedestrian environments

The effects of street greenery on the perceptual response to the acoustic comfort of pedestrian streets in traffic noise environments were examined through an experimental study that considered an audio-visual environment with no/low, medium, and high street greenery, dominated by road traffic, anthropogenic, and natural sounds. The results showed that the differences in the acoustic comfort evaluations without and with medium or high greenery were statistically significant. Under the effects of greenery, the acoustic comfort evaluation of each sound type dominating the environments without greenery increased by as much as one level, based on a five-point ordinal category scale. Considering various greenery conditions, dominant sound sources, and environmental functions, greenery was the most significant factor affecting acoustic comfort, and evaluations of pedestrian environments without greenery increased more in leisure environments (0.65–1.42) than in transportation environments (0.45–1.29) when road traffic sounds were at lower levels (50, 55, and 60 dBA) and anthropogenic and natural sounds were predominantly heard and influenced by street greenery. However, sound levels were the most significant factor affecting acoustic comfort when road traffic at 50–70 dBA was predominantly heard. Based on the negative linear relationships between sound levels and acoustic comfort evaluations for no/low, medium, and high greenery conditions, the evaluations affected by greenery increased with the increase in road traffic sound levels in transportation environments, whereas those influenced by either high or medium greenery in leisure environments tended to decrease gradually. These audio-visual perception-based findings provide reference guidance for PE quality optimization and related urban design considering comfortable sound environments.