Installed at the side or overhead of a road, a Changeable Message Sign (CMS) provides traffic information, educative information on government policies or other related messages released by relevant administrative units through communication and transmission networks. Numerous CMSs have been installed on Taipei City’s roads to offer traffic information, such as the messages of smooth traffic, heavy traffic, traffic jam, etc. All of the traffic information is obtained by calculating the traffic flow data collected by vehicle detectors installed on roads.