TOPIS is operating the management system of arterial road traffic to maximize road efficiency. The high-tech management system of road traffic adjusts signal operation schedules and changes road geometries to ease chronically congested areas by collecting traffic informations using detectors, taxi GPS and by analyzing heavily congested areas. In addition, the system detects unexpected situations, such as accidents, through thorough traffic monitoring and swiftly provides detour information in order to minimize traffic jams for the convenience of citizens. GPS is installed in approximately 72,000 taxis that continuously operate on the roads in Seoul. The system collects GPS data from taxis at two second intervals. Then, it processes GPS data and produces road speed data every two and a half minutes.