Research conducted at the Georgia Institute of Technology that investigated the use of geographic information system (GIS) technology as a support tool for coordinating traffic signals is discussed. TRANSYT-7F is the most widely used and respected macroscopic computer model for optimizing the coordination of traffic signals. Unfortunately, creating an optimum TRANSYT-7F model is very costly. The hypothesis of this research was that the use of a specialized GIS with TRANSYT-7F could enhance the process of coordinating a traffic signal system. The research resulted in the development of a GIS-based signal coordination system that operates on a microcomputer. This system is an improvement over existing methods of creating optimum TRANSYT-7F models because relationships between intersections do not have to be encoded manually. Instead, the system takes advantage of the GIS's topological data structure, which provides these relationships. The process of analyzing different network optimization scenarios is simplified with this system because the user need only to select the intersections to be coordinated from the GIS graphic display instead of cutting and pasting from existing TRANSYT-7F input files. Alternatively, the system can serve as a multipurpose signal information system and play a vital role in decision support. It can provide improved access to signal data and allows for swift identification of intersections that experience excessive delays or unacceptable levels of service.