Inclement weather particularly fog is the negative factor on traffic flow. In advanced countries, they control the speed in active way using Variable Speed Limit (VSL) depending on climatic condition so as to ensure the stable traffic flow is maintained. In this study, Variable Speed Limit signs with advanced visibility in inclement weather conditions was developed, which was then tested at KICT’s SOC R&D center at Yeoncheon through the off-road test and the performance of VSL was compared with conventional ones. Consequently, average legibility distance of newly-developed VSL was improved by 21.9% from the conventional ones.