prediction model in 1978 (FHWA model) [5], the model has been
widely used in many countries and proved effective [6–10].
Recently, a new highway traffic noise prediction model which uses
20 s continuous equivalent sound level [Leq(20 s)] as the basic
vehicular noise was developed by Tansatcha [11] and revised by
Pamanikabud [12]; the accuracy of the model was verified through
in-site measurement [11,12]. The Leq(20 s) model is believed to
provide accurate predictions by measuring the sound levels of individual
vehicles without assuming the vehicle noise source as a
point source. In the model released by FHWA, the energy mean
emission level at the reference distance is considered the basic
vehicular noise, and the vehicle noise source is assumed as a point
source. Considering that the FHWA model is built from a precise
mathematical derivation [5,13] and accepted by many countries