Concept 1 - What is a Coordination Pattern?

A Coordination Pattern in NTCIP is defined by a :

• cycle length (in seconds)
  

• offset (in seconds)
  

• split number
  

• sequence number

Go ahead and take a second look at the Pattern Table you entered in Step 3 under MM->2->4.

The sequence number refers to the phase sequences you entered under MM->1->2->4.  Most agencies develop standard phase sequence chart to select the sequence number desired for the pattern.

The split number references the split table that you entered under MM->2->7.  

The following timing plan was generated by Synchro

You have already programmed this plan as Pattern #1 in the controller:

Sequence #1	Ring1: 1  2  3  4  Ring2: 5  6  7  8
Pattern #1	Pat#  Cycle  Offset  Split   Seqnc    1     60      0       1       1
Split #1	Spl- 1  ø..1...2...3...4...5...6...7...8 ->  Time      10  20  10  20  10  20  10  20     Coor-ø    .   X   .   .   .   .   .   .      Mode      MAX MAX MAX MAX MAX MAX MAX MAX

Notice that only phase 2 is specified as the    Coor-ø   (coordination phase) rather than both phase 2 and 6.  Only one   Coor-ø   (coordination phase) phase should be specified because the main street phases may not begin or end together and you can only reference the offset at one point.

 

All of the patterns in these examples except Patterns 7,  8, 9 and 12 use   BegGRN   as the offset reference (verify this by going to MM->2->5 and scrolling to the right screen).  The following notation for the dual ring sequence in Pattern #1 below is used throughout this TecNote.  The "<" and ">" symbols (in red) reference the offset (in seconds) for the begin or end of the coord phase (C).

Pattern #1 - 60" cycle / 0" Offset Referenced to Phase 2 Begin-of-Green

1  / 10"

<0"(C)   2 / 20"

3 / 10"

4 / 20"

5 / 10"

6 / 20"

7 / 10"

8 / 20"

Concept 2 - Exploring Coordination With the Timing Status Screen

Run Coordination Pattern #1 by entering MM->2->1->1 ENTER

Go to the Timing Status Screen (MM->7->1) and observe the controller cycling through the phases for this pattern.  The sequence number is shown on this screen as well as the current phases being timed in each ring. The active vehicle (  Veh  ) and pedestrian (  Ped  ) calls are shown for each phase along with the phases which are Active and Next (  A/N  ). The   Loc   (Local) counter is the cycle counter which resets to zero at the offset point in the coordination cycle.

Fixed-time Operation

Notice that each phase is being forced off under coordination because of the   MAX   calls placed in the split table for Plan #1.    Term Fof    is displayed at the end of the split time for each phase and the controller is operating in a "fixed-time" mode with   MAX   calls applied to each phase. 

Also notice how the   Loc   (Local) counter resets to zero at the beginning of the coord phase (phase 2). With BegGRN (beginning-of-green) set, the beginning of phase 2 is the the offset reference point where    Loc   (Local) counter resets to zero.

Semi-actuated Operation

Now, change the   MAX   calls on phases 1, 3, 4, 5, 7 and 8 to   MIN  calls in Split #1 (MM->2->7->1).  Leave the    MAX   calls on phases 2 and 6 and consider these the main street through phases.  Then go back to the Timing Status Screen (MM->7->1) and observe the termination point of each phase. All phases other than 2 and 6 are actuated and terminate with a   Term Gap  because there are no detector actuations to extend the phases beyond the min time.  "Slack time" from each phase is passed along to the next phase in sequence.  The "slack time" eventually gets passed to phase 2 and 6 which now begin approximately 20" sooner than the fixed-time example.  Note that the   Loc  counter resets to zero 20" after the beginning of green of phase 2.

This operation is termed "semi-actuated" because the cycle is fixed and the main street phases pick up the "slack time" from the actuated phases until they are forced off.  A "fixed-time" controller guarantees a maximum split time for each phase within a fixed cycle time.   A "fully-actuated" controller does not have a coord phase or a fixed cycle time, and each phase is serviced on a first-come, first-served basis. 

 

Begin-of-green Vs. End-of-Green

The beginning of the coord phase is variable for "semi-actuated" controllers because the actuated phases are allowed to gap out and transfer a variable amount of "slack time" to the beginning of the coord phase.  

Go ahead and change the offset reference for Pattern #1 to  EndGRN  (right screen under MM->2->5) and compare the "semi-actuated" and "fixed-time" examples you observed with the offset reference set to begin-of-green.  

Pattern #1 - 60" cycle / 0" Offset Referenced to Phase 2 End-of-Green

1  / 10"

(C)0"> 2 / 20"

3 / 10"

4 / 20"

5 / 10"

6 / 20"

7 / 10"

8 / 20"

End-of-green insures that the offset is set to the end of the coord phase.  The   Loc  (Local) counter resets to zero at the end of the coord phase no matter how much slack time is passed to the beginning of the phase.  In other words, end-of-green coordination insures that your offset always "hits" when the coord phase goes to amber clearance.  Many users prefer end-of-green for this reason, because the offsets can be easily observed in the field when the through phases on the main street go to clearance.

PASSER 2 Offset References

PASSER 2 references the offset to the beginning of the first arterial phases at intersection #1 (intersection in the lower left-hand corner of the time-space diagram).  Therefore, make sure you adjust the offset from PASSER 2 so it agrees with the BEGIN or END of the coordinated phase you specify in the split table.

Here's an output from PASSER 2 for Intersection #1 (Master Intersection).

E Bear Val PE Bear Valley 
MAST INT = 0 SYS INT = 0 SYS OFFSET = .0 REF MOVMNT = 0 REF PNT = BEGIN

INTRSC 1 : Cottonwood COORD PHASE : 0 OFFSET : .0 SEC : 0.%
*-[MASTER INTERSECTION]
DUAL-RING PHASE #    5      6      1      2      3      4      7      8
PHASE SPLIT (SEC)   17.1   53.9   17.1   53.9   18.8   24.3   24.2   18.9
PHASE SPLIT (%)     15.%   47.%   15.%   47.%   16.%   21.%   21.%   17.%
PHASE REVERSAL       --     --     --    --      4      3     --     --
LEFT TURN           LEAD    --    LEAD   --     LAG    --    LEAD    -- 

In this example, the PASSER 2 offset is referenced to the beginning of phases 1 + 5 (LEAD LEAD sequence).  If you designate phase 2 as the coordinated phase in the controller, make sure you adjust the PASSER 2 offset to sync the offset at the beginning of the coord phase, not the beginning of 1+5.  The controller's offset should be 0" + 17" or 17" in this case.  Failing to reference the controller offset is a common mistake and leads to poor results when PASSER's output is misinterpreted.

 

PASSER 4 Offset References

PASSER 4 allows you to reference the system offsets to any intersection in the data set (called the Master Intersection).  You can specify the offset of the Master Intersection, the coordinated direction (north, south, east or west) and whether the master offset is referenced to the beginning or end of the coordinated direction.  All offsets calculated by PASSER 4 are adjusted to this master offset reference as shown below.

Here's an output of PASSER 4 offsets referenced to the beginning of each phase:

========= MOVEMENT-WISE MEASURES OF EFFECTIVENESS =============
NEMA PHASE        1     2      3     4     5     6     7     8
---------------------------------------------------------------
SPLITS (SEC)     32.6  38.6   15.0  33.8  15.0  56.2  15.0  33.8
PHASE REVERSAL    \___Y__/    \___N__/     \___N__/     \___N__/
OFFSET(%) TO BEG 42.8  10.6   70.0 82.5    10.6 23.1   70.0 82.5

Here's an output of the same PASSER 4 offsets referenced to the end of each phase.

========= MOVEMENT-WISE MEASURES OF EFFECTIVENESS ==============
NEMA PHASE        1     2     3     4      5      6     7     8
----------------- ----------------------------------------------
SPLITS (SEC)     32.6 38.6   15.0 33.8    15.0 56.2   15.0 33.8
PHASE REVERSAL    \___Y__/   \___N__/      \___N__/    \___N__/
OFFSET(%) TO END  30.0 2.8   42.5 70.6     83.1 30.0   42.5 70.6

PASSER 4's output is helpful to our application.  Just select the offset that corresponds with the BEGIN or END of the coordinated phase you specify in the split table.  You can also use PASSER 4's splits if you have been careful to maintain a one-to-one relationship between the phase numbers in the controller and the phase numbers in the controllers modeled with PASSER 4.

 

Concept 3 - Exploring Coordination With the Coordination Status Screen

Pattern #2 is identical to Pattern #1 in our last example.  We had you call up a new pattern rather than go back and reset all the changes you made to Pattern #1 in the previous exercise.

Pattern #2 - 60" cycle / 0" Offset Referenced to Phase 2 Begin-of-Green

1  / 10"

<0"(C)   2 / 20"

3 / 10"

4 / 20"

5 / 10"

6 / 20"

7 / 10"

8 / 20"

Run coordination Pattern #2 by entering MM->2->1->2 ENTER. 

Now, quickly go to the Coordination Status Screen (MM->7->2) and look for   Active-1  and   Next-2  which indicate the active pattern running in the controller and the pattern scheduled next.  If the controller is in phases 2/6 or  3/4/7/8, you will see the   Active    plan change to 2 when the controller crosses the barrier between phases 3/4/7/8 and moves to phases 1/2/5/6.    In this example, notice that the beginning of phase 2 and the offset are the same because a   MAX   call is applied to each phase and no "slack time" is passed to the beginning of phase 2. 

  OpModes, Src-TEST   tells you that the controller is running in  TEST  mode, rather than  TBC   (time-base coordination or time-of-day mode).  You can put the controller in  TBC  mode by entering MM->2->1->0 ENTER.  You can also manually force the controller into free operation by entering a value of 254 or flash operation by entering a value of 255 as a test mode.  (These values follow the NTCIP definitions for free and flash in TS 3.5 section 2.5.1 Coord Operational Mode Parameters).

Notice the two columns on the Coordination Status Screen labeled   Cycle   and   Ofst:  . 

The Cycle column shows the   Loc  and   Tbc   cycle counters and the current cycle length (  Prog- 60  ). 

The   Ofst   column shows the actual (  Actu:  ) offset, the current offset error (  Err:  ) and the current programmed (  Prog:  ) offset.  The error is the difference between the actual offset and the programmed offset you specified for the pattern.  

The controller will transition to the programmed offset using short-way, long-way or dwell offset correction (you specified this as a coordination mode in Step 2).  Once the controller achieves coordination, the actual and programmed offsets are the same, the offset error is zero and you will see   SYNC   displayed in the bottom right hand corner of the display.  The interpretation of the Coordination Status Screen will become obvious as you work through the transition examples.

Concept 4 - What is Time Base Coordination?

Call up the controller ID in StreetWise that you saved in Step 5 above and observe the coordination using the "General Information" screen.  This display allows you to view most of the information on the controller timing and coordination status screens. 

Time-base coordination uses midnight as a time reference to calculate the offset for the controller.  All coordinated signal systems maintain a time-base reference by zeroing the cycle counter at midnight and accumulating cycle times to the current time.  You can confirm this for the examples covered so far because a 60" cycle length resets the "TBC Counter" each minute.  Just watch the "General Information" screen and observe that the "TBC Counter" reaches zero on the even minute.  The "TBC Counter" provides the synchronization for all controllers in a coordinated system given that each controller's clock and the cycle length are the same.

The pattern offset is essentially an adjustment added to the "TBC Counter" to reference the beginning or end of the coordinated phase when the "Local Counter" reaches zero.  The "Local Counter" maintains the synchronization of the coordinated phase relative to the begin or end-of-green of the coordinated phase.  

When the offset is 0", the "TBC Counter" and the "Local Counter" are identical. In our next example, Pattern #3 calls for a 45" offset and you will observe that the "TBC Counter" and the "Local Counter" remain exactly 15" apart once the controller is out of transition.  If you use Microsoft Explorer, check out the Time-base Coordination Calculator to get a better understanding of the Tbc and Loc counters in the controller (this Javascript program only works with the Microsoft browser, not Netscape).

Just remember that the "Local Counter" is used to reference the beginning or end of the coord phase and the offset is used to adjust the "Local Counter" relative to the "TBC Counter" which is referenced to midnight.  If you understand this concept, then you understand time-base coordination.

Concept 5 - Short-way, long-way and dwell transition

This concept illustrates some of the concerns related to the Correction value chosen as a Coordination Mode in Step 2. The controller is still running Pattern #2 from our last example (60" cycle with a 0" offset). Now, change to Pattern #3 (60" cycle and 45" offset) by issuing the key sequence MM->2->1->3 ENTER.

After you force the controller to Pattern #3, look at the Coordination Status Screen (MM->7->2) and note that the   Active   plan is 2 and the   Next   plan is 3.  If the controller is in phases 2/6 or  3/4/7/8, you will see the   Active    plan change to 3 when the controller crosses the barrier between phases 3/4/7/8 and moves to phases 1/2/5/6.   During the transition, you will see the word   SHORT   in the bottom right hand corner indicating short-way transition.  Watch the offset error change from +15" to 0" as the controller moves to the new offset in Plan #3.  

Under short-way transition, the controller shortens each phase split time by 12% (the amount you specified under MM->2->5).  A 12% correction each cycle moves the offset from the 0" offset under Plan #2 "backwards in time" 15" to the new 45" offset specified in Plan #3. The controller is in coordination under Plan #3 when the offset error is zero and you see   SYNC   in the bottom right corner of the screen.

Pattern #3 - 60" cycle / 45" Offset Referenced to Phase 2 Begin-of-Green

1  / 10"

<45"(C)   2 / 20"

3 / 10"

4 / 20"

5 / 10"

6 / 20"

7 / 10"

8 / 20"

Now go back to Pattern #2 (60" cycle and 0" offset) by using the key sequence MM->2->1->2 ENTER.

Notice that   LONG   (or long-way) transition is used because you are moving "forward in time"  from a 45" offset in Plan #3 to a 0" offset in Plan #2.  The controller lengthens each phase split by 22% (the amount you specified in MM->2->5) to move the offset forward 15" to make this correction.  The controller will always use the quickest method, short-way (shortening the cycle) or long-way (lengthening the cycle) to make the offset correction.

 

A Common Pitfall When Using Short-way / Long-Way Transition

Pattern #4 calls for the same split table, sequence and offset as Pattern #3 (compare Pat# 4 with Pat # 3 in the Pattern Table under MM->2->4). Both patterns use begin-of-green to reference offsets and both patterns call for short-way / long-way transition (MM->2->1   Correction SHORT/LONG  ).

Pattern #4 - 60" cycle / 45" Offset Referenced to Phase 2 Begin-of-Green

1  / 10"

<45"(C)   2 / 20"

3 / 10"

4 / 20"

5 / 10"

6 / 20"

7 / 10"

8 / 20"

Run Pattern #4 and observe the Coordination Status Screen (MM->7->2).  Instead of seeing  SHORT  in the bottom right corner of the screen, you will see the word  DWELL  indicating that the controller is attempting to correct the offset by extending the coord phase each cycle.  However, the controller never achieves coordination and continues to  DWELL   with an offset error of -45" indefinitely.  

This condition occurs because when you initialized the controller in Step 1 the transition values for short-way, long-way and dwell in table MM->2->5 were initialized to zero.  The controller defaults to dwell correction when short and long-way values zero.  This is true even if the correction mode on screen MM->2->1 is set to  SHORT/LONG  rather than  LONG .  The controller will remain in  DWELL   correction indefinitely as long as the dwell value is 0" and will continue to time the cycle, splits and sequence correctively, but the offset will always be -45" out of step.  

Correct this problem by changing the Dwell value for Pattern #4 on screen MM->2->5 to 60".  Then observe the offset correction on the Coordination Status Screen (MM->7->2).  The controller will continue to show  DWELL   with an offset error of -45" until the beginning of the coord phase (in this case phase 2).  When the beginning of the coord phase is reached, the controller will "freeze" the  Loc  counter for the dwell time specified or until the offset error is reduced to zero.  When the offset  error  is reduced to zero, the DWELL indication changes to   SYNC   as before with short-way and long-way correction.

Dwell transition is the fastest way to correct offsets.  A dwell time equal to or greater than the cycle length always guarantees that the correction is made in one cycle by dwelling in the coordinated phase.  The downside of  dwell correction is that the minor phases are forced to wait up to one cycle while the controller dwells in the coordinated phase.  

The Naztec controller allows you to use short-way and long-way for some patterns and dwell for others.  Many users prefer to run short-way and long-way for patterns with long cycle lengths and dwell correction for shorter (off-peak) patterns.

Concept 6 - Know where your offset hits

Pattern #5 was taken from the following sequence given in the Synchro help file::

In this example, phase 2 and 6 are the main street phases which do not begin together because more split time is required for phase 1 than for phase 5.  Beginning-of-green can reference either phase 6 (TS2 - 1st Green) or phase 2 (Begin of Green).  If the offset is referenced to end-of-green, either main street phase may be specified because phase 2 and 6 end together.  The general rule to follow is:

Specify one coord phase and make the begin or end of this phase references the offset correctly that you generated with Synchro or one of the other timing models

Left-turns First Examples

Our next two controller patterns illustrate the difference between Synchro's "TS2-1st Green" and "Begin-of-Green" offset reference when the main street phases are staggered.  Run Pattern #5 using the key sequence MM->2->1->5 ENTER and observe that after Pattern #5 is active,  the   Loc  counter resets to zero at the beginning of phase 2.

Pattern #5 - 120" cycle / 0" Offset Referenced to Phase 2 Begin-of-Green

1  / 23"

<0"(C)       2 / 59"

3 / 14"

4 / 24"

5 / 16"

6 / 66"

7 / 18"

8 / 20"

 

Now, run Pattern #6 using the key sequence MM->2->1->6 ENTER and observe that after Pattern #6 is Active,  the  Loc  counter resets to zero at the beginning of phase 6.  Remember, your offset is the point in the cycle when the  Loc  counter resets to zero.

Pattern #6 - 120" cycle / 0" Offset Referenced to Phase 6 Begin-of-Green (TS-2 1st Green)

1  / 23"

2 / 59"

3 / 14"

4 / 24"

5 / 16"

6 / 66" <0" (C)

7 / 18"

8 / 20"

If Synchro and the controller do not use the same offset reference, your controller offset in this example can be as much as 7" from the offset calculated by Synchro (23" - 16").  If end-of-green was used instead of begin-of-green, it would not matter if phase 2 or 6 were specified as the coord phase because 2 and 6 end together. You can avoid these type of errors by using end-of-green rather than begin-of-green to reference the offset to the coordinated phase.  The next example proves that the offset is the same when end-of-green is used no matter if phase 2 or phase 6 is selected as the coord phase.

Run Pattern #7 with the offset referenced to the end of phase 2.  Then change the coord phase in the split table (MM->2->7->7 ENTER 1) from phase 2 to phase 6 and verify that the offset "hits" at the end of either phase 

Pattern #7 - 120" cycle / 0" Offset Referenced to Phase 2 End-of-Green

1  / 23"

(C)0"> 2 / 59"

3 / 14"

4 / 24"

5 / 16"

6 / 66"

7 / 18"

8 / 20"

When the phase sequence is left-turns-first, it is always easier to specify end-of-green for the offset reference because either main street phase (phase 2 or 6 in this example) may be chosen to reference the offset.  This avoids the pitfall of insuring that the coord phase agrees with Synchro's  "TS2 - 1st Green" or the "Begin-of-Green".  The next example illustrates another pitfall when end-of-green is used with a lead/lag left-turn sequence.

 

Lead/Lag End-of-Green Example

We will now look at two lead/lag patterns using the following Synchro output.  Note that ring sequence number 2 given in MM->2->4 provides the lead/lag sequence called for in this example.  All other examples so far have used sequence number 1 which is left-turns first. 

Pattern #8 - 60" cycle / sequence 6 / 0" Offset Referenced to Phase 2 End-of-Green

1  / 10"

(C)0"> 2 / 20"

3 / 10"

4 / 20"

6 / 20"

5 / 10"

8 / 20"

7 / 10"

Pattern #9 - 60" cycle / sequence 6 / 0" Offset Referenced to Phase 6 End-of-Green

1  / 10"

2 / 20"

3 / 10"

4 / 20"

6 / 20"           (C)0">

5 / 10"

8 / 20"

7 / 10"

Run patterns 8 and 9 and observe that the coord phases are different for each plan.  You must insure that the offset reference for the end-of-green coord phase agrees with the Synchro offset reference, otherwise the controller will not run the offset calculated in the Synchro model.

Synchro calls  EndGRN  the "Begin-of-Yellow" after the term used to reference offsets in the 170 controller.  Synchro defines the "Begin-of-Yellow" offset reference as "the beginning of the first main street phase to turn yellow" which is Pattern #9 in this example.  If phase 2 is designated as the coord phase, the Synchro offset reference and the controller offset reference will vary by 10". 

 

Concept 7 - Make Sure to Set Return Hold

The left-turns first examples under Concept 6 illustrated the advantage of using  EndGRN when the leading left-turns are staggered because either through phase can be specified as the coord phase.  When  BegGRN  is used and the leading left-turns are staggered, you need to make sure the coord phase agrees with the Syncro offset reference (TS-2-1st-Green or Begin-of-Green).  Otherwise, with  BegGRN  as the offset reference, the controller will not implement the Synchro pattern as intended.  This is not a problem for  EndGRN  because both through phase end together and either one can be specified as the coord phase. However, during lead/lag operation, the through phases do not begin or end together, so even with  EndGRN   selecting the correct coord phase is important.  

Begin-of-Green Offset Reference

The next two examples reference the offset (and the sequence change) at the "TS-2 Start of Green".
Pattern #10 - 60" cycle / sequence 6 / 0" Offset Referenced to Phase 6 Begin-of-Green

1  / 10"

2 / 20"

3 / 10"

4 / 20"

6 / 20" <0"(C)

5 / 10"

8 / 20"

7 / 10"

Pattern #11 - 60" cycle / sequence 11 / 40" Offset Referenced to Phase 2 Begin-of-Green

<30"(C)         2 / 20"

1  / 10"

4 / 20"

3 / 10"

5 / 10"

6 / 20"

7 / 10"

8 / 20"

Go ahead and change patterns from #10 to #11 and back to Pattern #10.  Observe the "General Information" screen in StreetWise and the Coordination Status Screen on the controller (MM->7->2).  These are the most difficult pattern changes that any controller has to deal with because the sequence changes on both sides of the barrier and the offset adjustment is almost a half cycle out of step.

Notice on that the sequence change occurs when the  Loc  counter resets to zero and the pattern becomes   Actv  (Active) on the Coordination Status Screen.  The offset will begin to adjust immediately when you change patterns; however, the sequence change does not occur until the  Loc  counter resets to zero.

Notice that when the sequence changes from Pattern #10 to Pattern #11, that several of the main street phases are skipped.  After this sequence change, the controller steps through the new sequence correctly without skipping any phases. 

 

Pattern 10	-> -> ->	Pattern 11
3+8
4+8
4+7
1+6 coord ø = 6	Sequence Change
		4+7
		4+8
		3+8

A similar sequence change is observed when the controller transitions from Pattern #11 to Pattern #10:

Pattern 11	-> -> ->	Pattern 10
4+7
4+8
3+8
2+5 coord ø = 2	Sequence Change
		3+8
		4+8
		4+7

Naztec Recommendations for NTCIP Coordination

NTCIP offers a tremendous amount of flexibility when developing coordination plans for semi-actuated controllers.   The following general recommendations should be considered to improve operations and avoid several pitfalls when the coordination modes and options are not set correctly.

Under Coordination Modes+ (MM->2->1)

1. Set Correction to SHORT/LONG coordination mode

2. Set Maximum to MAX_INH to avoid leaving a phase because of a max setting before the split times out

3. Set Force-Off to FIXED or FLOAT (the difference will be discussed in another TecNote)

4. Set Auto Err Reset to ON to allow a failed plan to recover during the next time-of-day change

5. Set Stop-on-Walk to ON to allow pedestrian times to extend past the split time specified.  If pedestrian movements are serviced frequently, you can always guarantee the ped time in your split

Under Transition, Coord ø+ (MM->2->5)

1. Always provide a short and long transition value or a dwell value - don't leave these values zero

2. Use EndGreen to reference the offset to avoid the problems discussed with staggered left-turns first

3. Always, always set RetHold

Under the Split Tables (MM->2->7)

1. Make sure your splits passes the diagnostic checks before you put your plan on the street

2. Use one coord phase and make sure your offset is referenced correctly with your timing model

3. If your coord phase is part of a lead/lag sequence, select the through phase that ends first as your coord phase to agree with Synchro's "Begin-of-Yellow" offset reference

4. Put MAX calls on all of your progression phases
   

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