Elements of Signal Timing

The essential elements that constitute pretimed signal timing are: (1) cycle length (2) interval length, (3) phase duration, (4) phase sequence, and (5) offset of yiel point. Fig. 11.19 illustrates these elements, which are discussed below.

Figure 11.19: Signal timing elements

The cycle length is the amount of time for the signal to complete one complet sequence of signal indications. In a coordinated signal system, the cycle length constant for all signals during any given control period. This is true whether the individual controllers are pretimed or actuated.

An interval is the smallest unit of measure used in defining a timing plan and is the segment of the cycle when all signal displays remain constant A phase is a combination of two or more intervals during which the traffic movements given the right of way remain unchanged. A phase is part of a cycle allocated to any combination of traffic movements receiving the right of way simultaneously during one or more intervals.

A signal cycle is composed of as few as two or as many as eight phases, depending upon the traffic movements that require protection during their respective green signal times. A two-phase operation is generally preferable in terms of traffic performance because it permits shorter cycle lengths and more green time for through movements. However,...