Transect-based analysis of the edge-to-interior noise gradient in a roadside urban park

Road traffic noise is a major environmental concern in cities, but how quickly sound levels drop as one moves inward from a park's road-facing boundary is often described only as an average trend. This study tested whether the rate of noise reduction changes abruptly at a specific distance inside a roadside urban park. Equivalent continuous sound levels (Leq, dBA) were recorded at six distances (۰, ۱۰, ۲۰, ۳۰, ۴۰, and ۵۰ m) along six transects perpendicular to the park edge in Isfahan, Iran. A segmented (piecewise) regression model was applied to detect a breakpoint in the noise-distance relationship. Mean noise declined from ۷۳.۶۹ dBA at the edge to ۵۷.۰۲ dBA at ۵۰ m (a ۱۶.۷ dBA reduction). A breakpoint was identified at ۲۲.۷۱ m. Before this threshold, noise decreased steeply at -۰.۴۷ dB per metre; after the breakpoint, the slope flattened to -۰.۰۸ dB per metre. The piecewise model provided a substantially better fit than a simple linear model (AAIC = ۱۶). These results reveal that traffic noise attenuation inside a park follows a two-phase pattern: a rapid reduction zone within the first ۲۳ m, followed by a zone of diminishing returns. Consequently, locating recreational areas or quiet zones at or beyond ۲۳ m from the road maximizes acoustic benefit relative to park depth.

کلیدواژه ها:

Traffic noise attenuation ، Urban park ، Piecewise regression ، Breakpoint distance