The purpose of this study is to integrate experimental design, systemsimulation, and GIS to develop an algorithm which can help grouping signals forbetter traffic operations. By definition, signal grouping is to clusterneighboring signals into a coordinated plan to smoothen traffic operations onroads. Many thresholds have been employed to determine if signals can be groupedtogether. Those thresholds include block length, road capacity, turningmovement, number of lanes, traffic flow direction, street corss section layout,etc. The application of those thresholds in signal grouping in the past tendedto use the superimposing or the annexing method. Therefore, this study employsthe approach of orthogonal array to test the threshold combination for signalgroupin. By doing this, a test network is designed which can represent thecharacteristics of most commonly seen street networks. Different combinations oftraffic flow, block length, etc. are then put together on the test network togenerate the efficiency of the threshold combinations. To test the efficiency ofa certain threshold combination, the CORSIM simulation program is used toproduce the MOE (measure of efficiency), and the program of TRANSYT-7F is usedto provide the timing plan for the signal network, It is therefore this researcha well designed and thorough experiment test. During the testing process, theGIS plays the role to provide the network characteristics which enhances theinterface of data provision and the display of output. In addition, thedevelopment of the Tainan City's signal GIS will later help to test thevalidation of the research result. Through coordination with ciyt signal controldivision, the result of the study is regarded as valid and solid by engineeringjudgement.