This paper describes the design development of a supervisory traffic decision support system with GIS support developed in conjunction with the real-time traffic control implemented in the city of Nottingham in the United Kingdom. The system architecture is based on DIstributed computers Memory Environment (DIME) harness, which provides communication facilities for external modules and programs to exchange real-time traffic data in a fast and reliable manner. Our paper introduces the overall decision support system and reports the results obtained while building the prototype. It also describes the GIS subsystem and the telecommunication subsystem for delivering on-line passenger information to mobile devices (e.g. mobile phone) using variety of approaches such as Short Message Service (SMS), Wireless Application Protocol (WAP) and TCP/IP over direct wireless connection.