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Coordination . Matt Wiesenfeld Darcy Bullock Purdue University. Sections. Introduction and Learning Objectives Terminology Becoming Familiar with Coordinator Status Screens Detector Mapping and Pitfalls Extension Time Adjustments Pitfalls Adjusting Splits on Minor Lefts
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Coordination Matt WiesenfeldDarcy BullockPurdue University
Sections • Introduction and Learning Objectives • Terminology • Becoming Familiar with Coordinator Status Screens • Detector Mapping and Pitfalls • Extension Time Adjustments Pitfalls • Adjusting Splits on Minor Lefts • Balancing Split Times Across Barriers • Reallocated Slack Green Time • Changing Cycle Length and Observing Impacts • Offset Adjustment • Leading and Lagging Left turns with Coordinator • Estimating Volume to Capacity Ratios • Integrating Synchro Outputs into VISSIM ASC/3 Database
1. Learning Objectives • The goal of this laboratory exercise is to explain critical coordinated system timing parameters and their effects on capacity allocation and platoon progression. When you have completed this laboratory, you should be able to: • Experiment with and explain how the three fundamental parameter sets, cycle, offset, and split, are used to define coordination. • Experiment with and explain how split times vary in a coordinated-actuated system, and how they operate in comparison to a fixed time system. • Experiment with and explain how the start of green in a coordinated-actuated system varies stochastically. • Experiment with and control the reallocation of unused green time by selecting appropriate operating parameters.
2. Network Terminology (Base Case) 1001 2001
2. Network Terminology (User Changes) 3001 4001
2. Left/Right Screens 2001 4001
2. Laboratory Intersections 4001 2001
2. MOST Interface Database Editor
3. Coordination Status • Any changes made on the Front Panel will only affect the current running of the simulation and can only be made while the simulation is running. • Changes in the database editor can only occur between runs but will remain until manually changed.
3. Coordination Status Questions to Consider • What defines Coordinated Operations? • How is green time allocated to different phases in a coordinated operation? • How do the front screen and the database differ? • What role do the virtual controller and the database serve in Laboratory 6.
3. Coordination Status Discussion • How do the virtual controller and the database editor differ? Why is this important in this laboratory? • What is the difference between ‘Free’ and ‘Coordinated’ Operation? • What defines Coordinated Operations? • How is green time allocated to different phases in a coordinated operation? • How is a split different then a max time?
4. Detector Mapping • Mapping Detectors to Phases provides a valuable link between the presence of vehicles and the allocation of green time. • A missed call on a detector can leave a vehicle sitting at a signal from more than one cycle. • Detector Calls assigned the wrong phases can provide unused green at intersections. • Simple checks using the controller can be made to insure that each detector is mapped to the appropriate phase.
4. Detector Mapping Questions • How would a detector become mis-mapped into a signal controller? • Why are missed calls particularly dangerous relative to a detector always making a call? • Beside mis-mapping, what can lead to poor detector operation? Pause at 350
4. Detector Mapping Discussion • How would a detector become mis-mapped into a signal controller? • Why are missed calls particularly dangerous relative to a detector always making a call? • Discuss design/documentation procedures that can be used to minimize the likelihood of mismapped detectors. • Beside mis-mapping, what can lead to poor detector operation?
5. Extension Times • Extension time allows the presence of a vehicle to extend green time through the allotted split. • Long extension times allow a single vehicle to extend green well beyond the time needed to move through the stop bar. • Short extension times lead to queue discharge being truncated midway through due to natural vehicle spacing. • Extension time, passage time, or vehicle extension time can be added either into the individual detector or the phase in the time plan. Placement in both will lead to double counting thus twice the time anticipated.
5. Extension Times Questions • Why would a signal engineer wish to design short extension times? • Why would a signal field engineer or technician desire longer extension times? • Where and why would placement of extension time be most useful considering all of the functions of detectors and timing plans? Pause at 460
5. Extension Times Discussion • Why would a signal design engineer wish to design short extension times? • Why would a signal field engineer or technician desire longer extension times? • Where and why would placement of extension time be most useful considering all of the functions of detectors and timing plans? • Where and when would ‘snappier’ operations be best and least well received?
6. Adjusting Splits on Minor Lefts • Minor street movements in a coordinated operation can only increase green time by taking green time from another minor or major movement. • Giving more of the split percentage to a minor left turn can be used to address a split failure. • These changes may affect other movements at the intersection, particularly those that must give up split time.
6. Adjusting Splits on Minor Lefts Questions • When it is reasonable to effectively move green time from a more heavily travelled movement to a less travelled movement? • Considering the barrier locations, what complications might have occurred if reallocate time had come from a major street movement instead of a minor street one? Pause at 350; 450; 550 Only Edits Phase 3 and 4 Splits in Step 5
6. Adjusting Splits on Minor LeftsDiscussion • When it is reasonable to move green time from a more heavily travelled movement to a less travelled movement? • Considering the barrier locations, what complications might have occurred if reallocate time had come from a major street movement instead of a minor street one? • What are potential complications of moving green time around a controller?
7. Balancing Split Times Across Barriers • Ring and Barrier structure allow two phases to operate simultaneously as long as these phases are in different rings and between the same barriers. An example would be phases 1 and 5 or 1 and 6 can run simultaneously in this structure. • Within a Barrier pair split can be moved easily between phases on the same ring. For example, 5% of the cycle could be transferred from 2 to 1 without any complication. • However, split cannot jump a barrier in one ring alone. If split is needed for phase 3 and the donor is phase 2, time from either 5 or 6 must be moved to either 7 or 8 in the example structure. This is important as often the need for green to be transferred across a barrier will only exist in one ring but must be accommodated in both.
7. Balancing Split Times Across Barriers Questions • What are the advantages of ring and barrier structure? • How is green time transferred within a barrier in a fixed force-off operation? • What is the consequence of not transferring time across the barrier in both rings? • How might time in a actuated coordinated operation move from phases 4 and 8 to 1 and 5 given fixed force-offs and extra green on the initial phases? Pause at 200 Edits to Table 9
7. Balancing Split Times Across Barriers Discussion • What are the advantages of ring and barrier structure? • How is green time transferred within a barrier in a fixed force-off operation? • What is the consequence of not transferring time across the barrier in both rings? • How might time in a actuated coordinated operation move from phases 4 and 8 to 1 and 5 given fixed force-offs and extra green on the initial phases? • What is the natural progression of a cycle if too little time is provided for the coordinated phase and too much for the other phases?
8. Reallocated Slack Green Time • The two main styles of green time reallocation are floating and fixed operation. • Floating Force-Offs ‘floats’ the initial Force-Off points effectively pushing all the extra green time to the coordinate movements whose barriers remain fixed in the same point of the cycle. • Fixed Force-Offs ‘fixes’ the phase Force-Off points allowing each phase to remain green until a time at which it would interfere with the originally allotted time for the next phase, or gaps out due to insufficient demand.
8. Reallocated Slack Green Time Questions • When it is reasonable to reallocate all available time to the coordinated movement? • If each phase in a fixed force-offs requires less green than its original allotment, would a field observer outside of the cabinet be able to distinguish it from floating operation? Pause at 150 Note Change in Figure 21
8. Reallocated Slack Green Time Discussion • When it is reasonable to reallocate all available time to the coordinated movement? • If each phase in a fixed force-offs requires less green than its original allotment, would a field observer outside of the cabinet be able to distinguish it from floating operation? • What are the advantages and disadvantages of floating and fixed force-offs. • Discuss the limitations of employing fixed force-offs everywhere and what caveats should be considered before making this transition.
9. Changing Cycle Length • Cycle length corresponds closely with queue length. • Short cycle lengths provide quicker servicing of each movement but also produce more lost time. • Longer cycle lengths provide more overall green time, but produce longer wait times for servicing of each movement. • Careful consideration of objectives, volumes, detection and coordination should be made before a cycle length type is defined.
9. Changing Cycle Length Questions • When would a shorter cycle length be appropriate? • When would a longer cycle length be appropriate? • Why in a coordination pattern would a long cycle length be used at a low volume intersection? Pause at 360
