Abstract: A method and computational aid for determining the optimum cycle lengths for use in a vehicular traffic control system wherein inbound and outbound traffic flow are equally favored. The method employs the technique of determining optimum cycle lengths by utilizing harmonic relationships found to exist between the time separations of the controlled arterial intersections and other key traffic control parameters. The method may be practiced by means of a highly simplified graphical computational aid which provides a clear visual indication of candidate optimum cycle lengths for a particular group of intersections which requires only prior knowledge of intersection relative locations. The unique format of the graphical computational aid provides, in addition to the candidate optimum cycle length information, a visual indication of the quality of the candidate solution obtained for each of the controlled intersections of the group.