1. INTRODUCTION
Traffic noise prediction models have been applied in many previous studies to plan more environment-friendly roads especially since the Federal Highway Administration (FHWA) released a traffic-noise model in 1978. However, most results of digital calculation in previous studies are noise levels in certain locations and cannot provide a full view of the study area [1]. Taking advantages of the function of spatial analysis and the geographical database, Geographic Information System (GIS) has been widely applied in traffic noise prediction in recent years. Pichai Pamanikabud et al. used GIS to analyze and forecast highway traffic noise and the system he developed enabled the analysts and planners to visually see and assess the impacts of traffic noise [2]. Bengang Li et al. developed an integrated noise-GIS system which provided the general functions for modeling different kinds of noise [3]. Manoj K. Jha et al. developed a GIS-based model for identifying highway segments for noise barrier installation and for calculating the effective length of noise barriers to be installed as well [4].