This study was conducted to analyze the runoff characteristics of the highway depending on the number of vehicles and to
provide the installation proposal of an NPS pollution reduction facility. There were a total of 5 monitoring sites used for the
study namely, Gyeongbu, Seohaean, Honam and Tongyeoung Dageon highway. Monitoring events started from 2006 until 2015
having a total of 44 storm events. According to monitoring statistics, the average antecedent dry days (ADD) and rainfall was
6.2 days and 19.2 mm, respectively. The Gyeongbu Highway (H-4) was recorded having the highest Average Daily Traffic and
Catchment Area (ADT/CA) with 49.4 car/day·m2 while other site were less than 10 car/day・m2. The average concentration
of the NPS pollutants generated from monitoring sites were 63.5 mg/L(TSS), 24.9 mg/L(BOD), 3.35 mg/L(TN), 0.63 mg/L(TP)
and 298 ug/L(Total Zn). This exhibited lower values in comparison to the remarks of highway related runoff EMC values published
in Korea. Moreover, through the results of the correlation analysis between the contaminant concentration and ADT/CA, R2
value of SS showed the highest correlation with 585. Through the correlation equation between ADT/CA and EMC of TSS,
when there is 73.7 mg/L of TSS EMC found from a domestic highway, ADT/CA ratio is normally 13 car/day・m2. Therefore,
in a case of more than 13 cars passing through a certain area, the area can be considered and present as the point of generation
of nonpoint source pollutants. Also, in this study, since it considered a unit area ADT indicated in previous studies, it was determined
that it has a high applicability and utilization in generalized units than conventional study which were conventionally done.