Adaptive Traffic Control Systems: Domestic and Foreign State of Practice (2010) / Chapter Skim
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Appendix A - Vendors' Descriptions of Major Adaptive Traffic Control Systems
Appendix A - Vendors' Descriptions of Major Adaptive Traffic Control Systems
Pages 51-82
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At the time of this APPENDIX A Vendors' Descriptions of Major Adaptive Traffic Control Systems References cited in this appendix can be found in Appendix C
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ACS Lite monitors traffic signals by polling each controller on a per-minute basis for time-stamped state changes. If a poll request fails, the status report is still available from the local controller until the end of the minute, so the system has ample opportunity to poll again.
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Configuration is limited to known facts, such as the location and dimensions of a detector. Adaptive Traffic Control Logic ACS Lite operates by monitoring traffic signals that are running normal, coordinated timing plans and then making incremental adjustments to split and offset parameters as often as every 5 to 10 min.
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Adaptive Traffic Control Logic BALANCE belongs to the generation of the newest German traffic signal control systems. Therefore, it is not relevant whether the existing traffic signals are controlled in fixedtime, traffic-actuated, or with public transport prioritization.
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FIGURE A3 Cyclic flows (blue) and green times for two-directional arterial link.
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A framework signal plan determines fixed or variable signal timings for all traffic signals in a coordinated group of signals. Within given framework plans, local intersection controllers can execute traffic-actuated operations based on the local traffic demand.
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A forecasting module of BALANCE estimates impacts of various traffic control strategies for the following time period by calculating performance measures such as delays, stops, and queue lengths for all intersection approaches. The performance measures are computed with the assistance of both mesoscopic and macroscopic BALANCE models.
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The use of InSync eliminates the need for static signal coordination plans. Adaptive Traffic Control Logic There are two aspects to InSync's signal optimization that deal with the conflicting objectives of providing the progression of platoons of vehicles along a main arterial and the clearance of vehicles involved with secondary traffic movements within the grid: the global and the local.
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so that vehicles are released from the downstream intersection as they arrive from the facilitator intersection. Using the travel times between each adjacent intersection these tunnel times are calculated by each intersection as it receives the dynamic tunnel phase timing messages from each adjacent intersection along the artery.
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Digital Signal Control Concepts -- Finite Number of Signal States (No Transition) InSync does away with set cycle lengths, set splits, and offsets to a fixed point in the cycle that have traditionally been considered essential for signal coordination.
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Interface Methodology -- Determination of Inputs Optimized Calls to Signal Controllers InSync is a plug-in technology that interfaces with all existing traffic signal controller and cabinet architectures. It controls traffic signals by submitting calls to the traffic controller through detector cards, just as inductive loops do.
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, which is the next critical piece of software running on the server (Adaptive Traffic Control System 2006)
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Download and upload features between the central system and local controllers are supported. Communication from the field 170 and 2070 Traffic Signal Controller is accomplished by the way of a 1200 baud twisted pair to a local area hub, terminating in a GDC Corporation multiplexer.
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. Adaptive Traffic Control Logic Within MOTION cycle time, split and stage selection is calculated to achieve favorable and balanced saturation levels for all intersection approaches.
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The local second-by-second actuated-traffic control of each intersection is still monitored by traffic engineers and carried out autonomously by the individual controllers. As a result of the use of local detectors a fast reaction to microscopic traffic changes by traffic-actuated stage length regulation is guaranteed.
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The algorithm uses measured as well as modeled demand to determine phase durations that are constrained only by minimum and maximum green times and, if running in a coordinated mode, by a virtual cycle length and offset that are updated based on real-time data. Originally, OPAC was developed as a distributed strategy featuring a dynamic optimization algorithm for traffic signal control without requiring a fixed cycle time.
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FIGURE A12 MOTION method of data substitute for faulty detectors.
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Over time the flexible cycle length and offsets are updated as the system adapts to changing traffic conditions. Adaptive Traffic Control Logic VFC-OPAC allows, from cycle to cycle, the yield point or local cycle reference point to range about the fixed yield points dictated by the cycle length and offset.
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OPAC architecture can use phone lines, fiber optics, or wireless communication media, but the reliability of communication is crucial for the proper operations of the system. If communication between central level and local controllers fails OPAC will run autonomously.
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Adaptive Traffic Control Logic Rather than reacting to changes in traffic conditions, RHODES uses peer-to-peer communications and predictive algorithms to identify upcoming changes and prepare accordingly. With RHODES, there is no explicit coordination; that is, there are no offsets and no fixed cycle lengths.
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Adapt is an adaptive control module that provides an interface between RHODES and the NextPhase traffic control software used on the 2070 ATC. AdaptEx provides similar functionality in an external module that interfaces with the ASC controller software.
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Adaptive Traffic Control Logic Strategic and Tactical Control In SCATS traffic control is affected at two levels, strategic and tactical. Strategic control is managed by the regional computers and is known as the Masterlink mode of operation.
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Optimal offsets on the higher flow links tend to minimize the total number of stops in the system, reducing fuel consumption and increasing the capacity of the network overall. Other SCATS Operating Modes Besides the real-time adaptive traffic control mode (Masterlink)
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SCATS also has the ability to internally manage several instances of the regional traffic control software on one physical computer. This provides flexibility in hardware configuration and for simulation use.
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SCOOT Adaptive Traffic Control Logic In SCOOT optimization of traffic control in the network is achieved using small, regular changes in signal timings designed to avoid major disturbance of traffic flow. Loop detectors are polled by the controller for occupancy every one-quarter second and typically transmitted once per second to the central computer, although the latest version of SCOOT relaxes this requirement.
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The Cycle Optimization operates on a region basis once every 5 min, or every two and one-half minutes when cycle times are rapidly changing. It identifies the "critical intersection" within the region (any of the intersections in a system or sub-area can determine the system cycle length)
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SCOOT is not constrained by a "master" intersection in determining system cycle lengths. Hardware and Software Requirements Standard Controller Firmware SCOOT runs with standard Siemens SEPAC firmware, the same firmware used for standard intersection control at 50,000 intersections across the United States.
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. Upstream detection provides a view of the traffic approaching an intersection in a TRANSYT type "flow profile." Utilization of the upstream detectors allows SCOOT to: • Be more sensitive to sudden changes in traffic conditions, • Be able to respond more quickly in congested conditions, • Calculate queue lengths more accurately, and • Base its changes on incoming "traffic flows," rather than latent "traffic demand." Special Features ASTRID and INGRID Data used by the SCOOT model in the optimization process such as stops, delays, flows, and congestion levels, are available to the user through the ASTRID (Automatic SCOOT Traffic Information Database)
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To achieve stability and robustness at the network level, interactions are defined between the local level and the central level. At the central level, the optimal network traffic control problem is developed based on the macroscopic traffic model of the network, and control strategies such as minimum, average, and maximum length of each stage, offsets, and weights for all the elements constituting the objective function optimized locally are defined for each intersection.
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The higher level is responsible for setting the network control strategies, whereas the lower level (SPOT -- at local intersection controllers) implements signal timings according to the actual local traffic conditions constrained by the network control strategy from the higher level.
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Special Features Plan Selection Strategies These traffic control strategies are suitable for networks with predictable TOD and DOW traffic patterns. Once a set of typical signal timing plans is defined (based on the historic traffic data from detectors)
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when the public transit vehicle is approaching the intersection. In this way, it ensures that the traffic signal phases are managed in a way that minimizes the impact on other vehicles.
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