Recent researches show that the traffic fatality rate in fog is higher than that in rain and snow. In that sense, methods to measure visibility accurately and to notify the measured visibility information to drivers are required. We thus developed a system for measuring the road visibility in realtime by employing CCTV cameras. In this paper, we also propose a wide-area visibility information system through measuring the visibility of every highway by using the developed system. The proposed wide-area visibility information system uses the video clips from the CCTV camera instead of the output from the expensive fog sensor. Hence, we expect that it can reduce the cost of installation and operation dramatically and the measured visibility information has a number of applications.