All the noise maps, produced with IDW interpolation method, would have a
limitation to provide accurate exposure levels of road traffic noise. According to Sheng
and Hu (2003), the distance-decay model of sound propagation has some assumptions
such as free and roughly homogeneous propagation medium, i.e. air, and weather
condition. Besides, in an urban environment, sound propagation will be affected by
artificial spatial objects such as buildings and noise barriers.