Coordination

Matt WiesenfeldDarcy Bullock

Purdue University

Sections

1. Introduction and Learning Objectives2. Terminology3. Becoming Familiar with Coordinator Status Screens4. Detector Mapping and Pitfalls5. Extension Time Adjustments Pitfalls6. Adjusting Splits on Minor Lefts7. Balancing Split Times Across Barriers8. Reallocated Slack Green Time9. Changing Cycle Length and Observing Impacts10. Offset Adjustment11. Leading and Lagging Left turns with Coordinator12. Estimating Volume to Capacity Ratios13. 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 Screens40012001

2. Laboratory Intersections40012001

2. MOST Interface

Run Continuously

Run Single Step

Pause

Stop

Database Editor

2. Detector Mapping/Ring & Barrier

1 2 3 4

5 6 7 8

3. Coordination Status Network

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

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 (1)

5. Extension Times (2)

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

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. Splits

Split = s % × C

Clearance

Cycle Length

l1 e

Red Green Indication Y R

G = Split – Y i – R i

Effective Gree

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; 550Only 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?

1 2 3 4

5 6 7 8

7. Balancing Split Times Across Barriers

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 200Edits 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. Allocation of Slack Time

8. Reallocated Slack Green Time(2)

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. Slack Reallocatoin: Float/Fixed FO

(a) Effective Splits with Maximum Recall

(b) Effective Splits with Floating Force-Offs

(c) Effective Splits with Fixed Force-Offs

1 3

6

2

5

4

7 8

17% 17%

17% 17%

38%

38%

28%

28%

1 3

6

2

5

4

7 8

17% 17%

17% 17%

38%

38%

28%

28%

1 3

6

2

5

4

7 8

17% 10%

17% 10%

38%

38%

28%

28%

1 3

6

2

5

4

7 8

17% 17%

17% 17%

45%

45%

28%

28%

1 3

6

2

5

4

7 8

17% 10%

17% 10%

38%

38%

30%

30%

1 3

6

2

5

4

7 8

19% 17%

19% 17%

41%

41%

28%

28%

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 150Note 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 (1)

9. Changing Cycle Length (2)

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. Cycle Length

Cycle Lengt h

MaxMax Max Max

Split Split Split Split

1 2 3 4

5 6 7 8

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

9. Changing Cycle Length Discussion

• 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?

• How does cycle length effect queuing?

• At signals in or near interchanges, how would cycle length effect operations?

• List factors which would affect cycle length decisions?

9: Cycle Lost Time/Efficiency/Reality

Lost Time • 5s per phase• 20s per cycleEfficiency• 60 s cycle

– (60-20)/60=67%

• 120 s cycle (84%)• 240 s cycle ( 92%)

– Quadruple Delay,– Gain 8% theoretical

capacity

0 60 120 180 240 300 36060%

65%

70%

75%

80%

85%

90%

95%

100%

Section 9Offset Adjustment

• Offsets allow a coordinated system to return green to a coordinated movement at a predictable point in the signals operation.

• A good offset will facilitate continuous movement for a platoon of vehicles along the coordinated route.

• Good offsets are difficult to achieve in both directions. Compromising is often necessary between the coordinated directions.

• Stochastic variation in start of green for the coordinated movement at an actuated intersection can cause some complication. The approach used in this example is empirical and can be explained more thoroughly in quantitative and graphical methods.

10. Offset Adjustment (1)

10. Offset Adjustment (2)

10. Offset Adjustment

• How in the field could a poor offset be detected?

• Why is planning a good offset in both directions along a standard arterial roadway difficult?

• How does actuation cause stochastic variation in green start times?

Pause at 200

10. Which has better progression

(a) Phase 2

(b) Phase 6

GreenRed

GreenRed

10. Offset Concept

Time-Space Space-Time

Distance

TimeOb

Adjustment

1st St.

2nd St.

3 2

3 4 1 2

14

time

space

Off

set

Distance

vehicle trajectory

#2#1 Directionof Travel

Red

Red

Red

Red

10. Offset Adjustment Discussion

• How in the field could a poor offset be detected?

• Why is planning a good offset in both directions along a standard arterial roadway difficult?

• How does actuation cause stochastic variation in green start times?

• What are some strategies for overcoming stochastic

variation?

11. Leading and Lagging Left Turns

11. Leading and Lagging Left Turns• Phase sequencing controls which phases occur after each other in

the cycle. Two common types are leading and lagging in reference to left turning movements.

• Leading is phase sequencing that provides green to the left turn phase on a roadway and then afterwards, the opposite adjacent through movement phase will be provided green.

• Lagging is phase sequencing in which the through movement receives green first and the turn movement opposite adjacent receives green after the through movement.

• Changing sequencing from Leading to Lagging can advance the start of green on the through movement by at most the entire left turning split. This change effect both the “Early Return to Green” and the nature of “Offsets”

11. Coordination is a Two Way ProblemLead-Lag can help fit windows

Distance

TimeOb

Adjustment

1st St.

2nd St.

3 2

3 4 1 2

14

11. Leading and Lagging Left Turns Questions

• How would lead/lag changes affect left turn delay?

• What is a possible queuing pitfall of lagging left turns?

• Why would phase sequencing be used as a tool when offset is available?

• Why is it not advised to change phase sequencing often along a continuous arterial?

Pause at 220

11. Lead/Lag Phase Sequencing

Leading (1-5) Sequence 1 Lagging (1-5) Sequence 6

11. Leading and Lagging Left Turns Discussion

• How would lead/lag changes affect left turn delay? • What are the ramifications of lagging left turns? • Why would phase sequencing be used as a tool

when offset is available? • Why is it not advised to change phase sequencing

often along a continuous arterial?

12. Volume to Capacity

• Volume to Capacity Ratio (v/c) refers to the actual number of vehicles passing through an intersection in comparison to the number that could have. Conventional wisdom indicates the lower the v/c the better the operation.

• Capacity at a signalized intersection for a specific lane of a specific movement is a product of the green provided. The calculations in the experiment are simplified to illustrate principles of volume to capacity ratios.Pause at 480

Table 11 Discussion

12. Volume to Capacity Questions

• How is v/c related delay?• How is v/c related to queuing?• Why would a properly functioning actuated

intersection not have a low v/c even when volumes are low?

• How is v/c different at an actuated traffic signal compared to a stop controlled intersection?

12. Volume to Capacity Discussion• How is v/c related to delay?

• How is v/c related to queuing?

• Why would a properly functioning actuated intersection not have a low v/c even when volumes are low?

• How is v/c different at an actuated traffic signal compared to a stop controlled intersection?

• How does v/c at an actuated intersection related to intersection utilization?

12. Example 8 phases/24 hours

P1 P2 P3 P4

P5 P6 P7 P8

0:00 24:0012:00 0:00 24:0012:00 0:00 24:0012:00 0:00 24:0012:00

1.0

0

0.5

Time of Day

Vo

lum

e t

o C

apa

city

Rat

io

1.0

0

0.5

P1 P2 P3 P4

P5 P6 P7 P8

P1 P2 P3 P4

P5 P6 P7 P8

0:00 24:0012:00 0:00 24:0012:00 0:00 24:0012:00 0:00 24:0012:00

1.0

0

0.5

1.0

0

0.50.5

Time of Day

Vo

lum

e t

o C

apa

city

Rat

io

1.0

0

0.5

1.0

0

0.50.5

74

13. Integrating Synchro with NTCIPOpportunities and challenges

Engineering Judgment

Engineering Analysis

WeekdaySaturday

Sunday

a) Typical 24-hr Flow Pattern

Morning Timing Plan

Evening Timing Plan

Mid-day Timing Plan

c) Morning Synchro Analysis Timing Report

d) Controller and Intersection

WeekdaySaturday

FreeMorning Plan

Mid-day PlanEvening Plan

Free

Sunday

b) Discrete Design Volumes

75

13. Synchro Deployment Process

Morning Timing Plan

Evening Timing PlanMid-day

Timing Plan

Good Default

Signal Timing DB

76

13. Idealized Synchro Deployment

Engineering Judgment

Engineering Analysis

WeekdaySaturday

Sunday

a) Typical 24-hr Flow Pattern

Morning Timing Plan

Evening Timing Plan

Mid-day Timing Plan

c) Morning Synchro Analysis Timing Report

f) Controller and Intersection

WeekdaySaturday

FreeMorning Plan

Mid-day PlanEvening Plan

Free

Sunday

b) Discrete Design Volumes

d) Relevant UTDF Parameters for Morning Plan

RECORDNAME INTID DATA

Cycle Length 6 80

Referenced To 6 1

Reference Phase 6 206

Offset 6 45

e) UTDF to NTCIP

UTDF NTCIP ASC

Cycle LengthpatternCycleTime.11.3.6.1.4.1.1206.4.2.1.4.7.1.2.1

= 80

Reference Toasc3crdOffsetRef1.3.6.1.4.1.1206.3.5.2.13.4

= Yell

Reference Phase

splitCoordPhase.3.(2 / 6)1.3.6.1.4.1.1206.4.2.1.4.9.1.5.3.21.3.6.1.4.1.1206.4.2.1.4.9.1.5.3.6

= 1= 1

OffsetpatternOffsetTime.11.3.6.1.4.1.1206.4.2.1.4.7.1.3.1

= 45

77

13. Synchro Design Volumes

78

13: Synchro Output

• Synchro Software – Actuated

Coordinated– Cycle Length

Defined– Splits Optimized

79

13. Deployment of Synchro

80

13. Synchro Data Structures

81

13. SynchroNTCIP

82

13. Deploying Synchro Timings is More Complicated than Simple 1:1 Conversion

i) Direct Mapping

Walk = 4 sec Walk = 4 sec

ii) Mapping with Translation

All Red = 1.5 sec Red Clear = 15 tenth of sec

iii) Mapping with Engineering Judgment

Max Green + Yellow + All Red = 30seconds Split Time =

30 sec

iv) Missing Design Elements

???’s Force-off Mode

Lowest Risk

Highest Risk

UTDF Example Parameter

NTCIP Example Parameter

83

13 (i) Walk: Mapping Directly

i) Direct Mapping

Walk = 4 sec Walk = 4 sec

ii) Mapping with Translation

All Red = 1.5 sec

Red Clear = 15 tenth of sec

iii) Mapping with Engineering Judgment

Max Green + Yellow + All Red = 30seconds

Split Time = 30 sec

iv) Missing Design Elements

???’s Force-off Mode

Lowest Risk

Highest Risk

UTDF Example Parameter

NTCIP Example Parameter

84

13 (ii) Red Clear: Mapping with Transition

i) Direct Mapping

Walk = 4 sec Walk = 4 sec

ii) Mapping with Translation

All Red = 1.5 sec

Red Clear = 15 tenth of sec

iii) Mapping with Engineering Judgment

Max Green + Yellow + All Red = 30seconds

Split Time = 30 sec

iv) Missing Design Elements

???’s Force-off Mode

Lowest Risk

Highest Risk

UTDF Example Parameter

NTCIP Example Parameter

85

13 (iii) Split Time: Mapping with Engineering Judgment

i) Direct Mapping

Walk = 4 sec Walk = 4 sec

ii) Mapping with Translation

All Red = 1.5 sec

Red Clear = 15 tenth of sec

iii) Mapping with Engineering Judgment

Max Green + Yellow + All Red = 30seconds

Split Time = 30 sec

iv) Missing Design Elements

???’s Force-off Mode

Lowest Risk

Highest Risk

UTDF Example Parameter

NTCIP Example Parameter

86

13 (iv) Force off Mode: Missing Design Element

i) Direct Mapping

Walk = 4 sec Walk = 4 sec

ii) Mapping with Translation

All Red = 1.5 sec

Red Clear = 15 tenth of sec

iii) Mapping with Engineering Judgment

Max Green + Yellow + All Red = 30seconds

Split Time = 30 sec

iv) Missing Design Elements

???’s Force-off Mode

Lowest Risk

Highest Risk

UTDF Example Parameter

NTCIP Example Parameter

87

13. Syncrho NTCIPMapping Overview