Module 7 : Traffic Signal Design

Lecture 39 : Vehicle Actuated Signals

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	Concept of Full-Actuated Controller Principles Detectors on all approaches. Each phase has a preset initial interval. Phases are sequenced according to "calls" for service on all approaches. Green interval is extended by a preset unit extension for each actuation after the initial interval provided a gap greater than the unit extension does not occur. Green extension is limited by preset maximum limit. Generally Point Detectors are used. Detectors can be placed at either stop line or upstream location. Figure 1: Full-Actuated Control Advantages Reduces delay relative to pre-timed control by being highly responsive to traffic demand and to changes in traffic pattern. Detection information allows the cycle time to be efficiently allocated on a cycle-by-cycle basis. Allows phases to be skipped if there is no call for service, thereby allowing the controller to reallocate the unused time to a subsequent phase. Disadvantages Initial and maintenance cost is higher than that of other control types due to the amount of detection required. It may also result in higher percentage of vehicles stopping because green time is not held for upstream platoons. Concept of Volume-Density Controller Volume-Density Controllers are designed for intersections of major traffic flows having considerable unpredictable fluctuations. They are generally used at intersections with high approach speeds ($\geq$ 45 mi/hr). Here, detectors are placed on all approaches. Generally this type of controller is used with Area Detectors. To operate efficiently, this type of control needs to receive traffic information early enough to react to existing conditions. So, it is essential that detectors be placed far in advance of the intersection.