TecNote 1202 - Diamond Coordination by Example

Naztec TS2 and 2070 controllers comply with section 2.8 of Texas Department of Transportation Specification TO-4048. "Diamond Operation" is also discussed in Chapter 11 of the Naztec Operations Manual for NTCIP Based ATMS Controllers. 

This TecNote is a sequel to TecNote 1201 - Texas Diamond Modes in Free Operation. You are encouraged to review this TecNote first to gain an understanding of  4-phase, 3-phase and separate intersection diamond modes in free operation before dealing with the coordination issues in this TecNote. TecNote 7001 - Modeling 4-Phase Diamond Interchange Operation with Synchro/SimTraffic provides examples of 4-phase coordination modeled with Synchro/Sim Traffic.

The coordination examples in this TecNote apply to all Naztec TS2 and 2070 controllers.  A Diamond Coordination Excel Spreadsheet is provided to help you program the split times for the coordination patterns in these examples (you may also download this spreadsheet as a .zip file). This worksheet allows you to model  minimum phase times with any shortway applied to insure that the split times will pass the controller diagnostics. The spreadsheet also models the travel time distances discussed in TecNote 1201 to calculate split times for the frontage road extensions.

It is assumed that you have a good understanding of basic coordination of standard eight phase (STD-8) coordination.  Therefore, if you are having difficulty with any of the basic concepts in this TecNote, please visit the following links on our site:

TecNote 1101 - NTCIP Coordination By Example  

TecNote 3010 - NTCIP Database Guidelines Part I

TecNote 3011 - NTCIP Database Guidelines Part II

This TecNote contains Macromedia Flash animations of 2070 scan screens captured from StreetWise.  The animation shows phase sequence changes for the different modes of diamond operation with annotations to point out the unique features of each operation.  If you cannot view these animations from your web browser, you will need to click on the following button to install the Flash 6 plug-in.


Flash 6 Plug-in

Initialize the Controller as a DIAMOND

Note: All keystroke notations used in Naztec TecNotes are referenced to the Main Menu (MM).  The Main Menu is accessed using the red MAIN/DISP key on the TS2 controller or the white "star" ( * ) key on the 2070 controller.

You should initialize your controller as a DIAMOND now even if you initialized the controller in TecNote 1201 - Texas Diamond Modes in Free Operation. This will insure that your controller database is at a known starting point to following the exercise below.

Initializing the controller requires the run timer to be disabled to insure that the cabinet is safely in flash when the database and configuration of the controller is reset. Turn the run timer OFF from menu MM->1->7 and initialize the controller as a DIAMOND from MM->8->4->1. After the initialization is DONE, turn the run timer back ON from menu MM->1->7.


MM->8->4->1: Initializing the Controller as a DIAMOND

You learned in TecNote 1201 that initializing the controller as a DIAMOND programs the following parameters in the controller database for you:

Coordination Modes for Diamond Coordination

The following NTCIP coordination modes under MM->2->1 (left-menu) must be set for diamond coordination.  The NTCIP Force-off value OTHER enables the Force-off+ value programmed in the right menu.  The Correction setting must be set to SHORT/LONG because we will apply shortway transition in these examples.  The Maximum setting is typically set to MAX_2 with the phase max2 phase times set high enough under MM->1->1->1 so the phases won't max-out in coordination before the force-off is applied.


MM->2->1 (left menu): NTCIP Coordination Modes

EASY coordination is covered in Chapter 13 of the Naztec controller manual (see section 13.2).  The Force-off+ value under MM->2->1 (right menu) must be set to EASY for diamond coordination. If you want slack time to move to the coord phase rather than to the next phase in the sequence, then set Easy Float to ON. One of the examples in this TecNote how Easy Float works, so for now leave it OFF as shown on the example screen below.

Be sure to set Stop-in-Walk to ON in these examples or you will generate coord diagnostic errors because the splits are shorter than the default pedestrian times. Stop-in-Walk is discussed at length in the controller manual and in the other TecNotes related to coordination. Basically, if you permit an occasional pedestrian service to overrun the split time, you can set Stop-in-Walk ON and run shorter split times than if you had to satisfy the pedestrian times each cycle (with or without a ped call).

The EASY force-off method requires that the offset is referenced to the  Begin-of-Green of the Coord-Ø (i.e., the End-of-Green offset reference under MM->2->5, right menu, does not apply when EASY based force-offs are used).


MM->2->1 (right menu): Coordination Modes+

Timing Constants Required for the Diamond Coordination Spreadsheet

TecNote 1201 provides several animations illustrating the use of Ø12 and Ø16 to extend the frontage road overlaps at the initial start of Ø2 and Ø6.  The maximum split time for Ø12 during coordination cannot be larger than the travel time for vehicles moving right-to-left through the interchange from Ø6. The maximum split time for Ø16 during coordination cannot be larger than the travel time for vehicles moving left-to-right through the interchange from Ø2 . Therefore, during 4P (4-phase) coordination, the split times for Ø12 and Ø16 must be limited to these travel times to insure that the downstream signals are green when the platoons from Ø2 and Ø6 arrive at the downstream signals.


4-Phase Operation - Frontage Road Extensions Ø12 and Ø16 Based on Travel Times

Sheet I. Timing Constants (Excel spreadsheet) allows you to specify these travel times to insure that the controller minimum phase times are not violated.  You can model Shortway% and exclude shortway for up to 4 "No Shortway Phases".  For 4P (4-phase) operation, it is advised that you exclude Ø4, 8, 12 and 16 from shortway because this reduces the minimum split times for the frontage roads.  For these examples, code the phase minimums and travel times as follows:.

Note that the travel time moving LEFT to RIGHT from Ø2 is 4".  This violates the travel time check because if the minimum split for Ø16 is 5".  The end of the frontage road overlap timed with Ø16 will extend 1" longer than the arrival of vehicles from Ø2 forcing them to stop.  For this example, assume that the travel times in both directions is 5".  This will satisfy the minimum vehicle times for the frontage road extension phases Ø12 and Ø16.  However, in practice you would want to measure the travel times for each diamond with a stop watch and provide some reasonable value to insure that vehciles traveling through the diamond are not forced to make a dead stop at the downstream signal.

Go ahead and make sure that the phases times in your controller (MM->1->1->1) agree with the values in this table.  Set the Min Grn for Ø1-8 to 4" and for Ø9-16 to 1".  Change all the yellow clearance times to 3.0" and all-red to 0".  Note that the minimum split times are based on the shortway provided in the spreadsheet.  A 1" buffer is added to the minimum split time if the Min Green is set less than 2".

Set the shortway to 12% for the first 7 patterns under MM->2->5 as shown below:  Also, exclude shortway for the frontage road phases and extensions (Ø4, 8, 12 and 16) for patterns 1-4 because these will be set to 4P (4-phase) operation.  Excluding shortway for the frontage road phases and extensions helps keep the minimum split as low as possible.


MM->2->5: Exclude Frontage Road Phases and Extensions for Pat# 1-4

Set up the Pattern Table and Diamond Mode for Each Pattern

The Pattern Table is programmed under MM->2->4.  In these examples, we will setup patterns 1-4 to run 70" cycles under 4P (4-phase) coordination.  Patterns 5-6 will run 60" cycles under 3P (3-phase) coordination and pattern 7 will be a SEP (separate intersection) example.


MM->2->4: Pattern Table for Diamond Coordination Examples

Note that the Sequence is set to "1" for all seven patterns.  It doesn't really matter what sequence number you specify because the Diamond Mode selected will set the pattern to 97 (for 4-phase), 98 (for 3-phase) or 99 (for separate ring) operation.  You specify the Diamond Mode for each pattern in the right menu under MM->2->6:


MM->2->6 (right menu): Diamond Modes Programmed For Each Pattern

4-Phase Diamond Mode Coordination

Sheet II. 4-Phase Operation (Excel spreadsheet) helps you program the split tables for 4P (4-phase) coordination.  Here is our first example for Split Table #1.  Please enter the values as shown in the blue boxes bounded by the magenta borders. You supply the cycle length from the Pattern Table and the split times for all the movements entering the diamond.  The spreadsheet sets the split times in the split tables below so you can cut and paste these values directly into StreetWise.


Pat# 1 Example - 4-Phase With Frontage Road Extensions and All Phases Called

Program these values into Split Table# 1 as shown below.  Set Ø2 as the Coord-Ø and set the Mode to MIN for Ø1, 4, 5, 6 and 8 and MAX for Ø2. Do not recall Ø3 or Ø7 because these phases are not enabled. Then, force the controller into Pattern # 1 by setting Test_OpMode to "1" under MM->2->1. 


MM->2->7->1: Split Table #1 (4-Phase Example With Ø2 and Ø6 set to MAX)


MM->2->7->1 (right menu): Phase 9-16 values for Split Table# 1-3

The coord diagnostic should read OK (MM->2->8->5). If the diagnostic indicates there is a "Phase Time error on Ø4", go back and read the instructions about Stop-in-Walk under Coordination Modes+ above.  If the coord diagnostic indicates that "SPLIT=0, PH = 003", then change your Mode setting for phases 3 and 7 to NON. Recalling a phase that is not enabled, enables that phase and generates an error because the split time has to be greater than 0 for an enabled phase.

Check that pattern 1 is active in TEST mode under MM->7->2 and that the controller is in SYNC.  Now, observe the Timing Status under MM->7->1 for Pattern# 1.  You can also tell from this screen that the controller is coordinated because the Loc (local) cycle counter is timing. The active sequence is 97 which was set by the controller when the Diamond Mode for this pattern was programmed as 4P (4-phase).

This is all that is required to coordinate a 4-phase diamond.  The animation below lets you the sequence change from the drivers perspective. The 4P (4-phase) diamond goes "around-the-clock" (clockwise) using the 4-phase sequence Ø2-4-6-8 like we saw in TecNote 1201 - Texas Diamond Modes in Free Operation. What is important to note about Pattern# 1 is that Ø2 is the Coord-Ø and that Ø2 and Ø6 are being serviced with MAX calls.  This will lead into our next example using Pattern# 2.


Pattern #1

Spreadsheet Diagnostics

If you use the spreadsheet to build your patterns, you can catch coord errors before you download the pattern to the controller.  Go back to the spreadsheet and make the following changes to exercise some of the checks built into the spreadsheet:

  1. Change the split time for Ø2 from 24" to 20".  This generates: "Error! Ø2+4+6+8 must equal cycle, not 66".  You can easily add 4 seconds to Ø2+4+6+8 to correct this error.  Go ahead and add 4" to Ø6 making it 32".
     

  2. Change the split time for Ø2 from 20" to 5".  You could correct the cycle length error by adding 15" to Ø2+4+6+8, but there is a Min Check Error on phase 2 in the split table. The controller coord diagnostic would also catch this error for you; however, the spreadsheet is designed to help you catch these problems before you try to activate them in the controller. 

    Looking back at sheet "I. Timing Constants", you will see that the minimum split time is 13". This minimum is also provided in parenthesis next to the label for Ø2.  So change Ø2 to 13" and balance Ø2+4+6+8 so the cycle length is 70".  Note that in 4-phase operation, the minimum split time for Ø2 is the sum of the min vehicle times for Ø2 + Ø16.  Likewise, the minimum split time for Ø6 is the sum of the min vehicle times for Ø6 + Ø12.
     

  3. Change Ø12 from 5" to 15".  First, notice that the cycle length is not violated when you changed the split for Ø12 like the last example. The cycle length equals the sum Ø2+4+6+8.  Ø12 times concurrently with Ø6 and is not included in the cycle length calculation. 

    The error now currently reads, "Extension>travel time right to left".  Basically, you have allowed the frontage road extension, Ø12 to exceed the travel time for vehicles moving right to left from Ø6.  The spreadsheet checks the split specified for Ø12 with the travel time you supplied in sheet I.
     

  4. Change Ø12 from 15" to 3".  The split is now less than the travel time, so the error "Extension>travel time right to left" goes away.  However, the split for Ø12 is now less than the minimum phase time for Ø12, so there is a "Min Check" Error under Ø12 in the split table.

    Change Ø12 from 3" to 5" to remove this error. The frontage road extensions are must be greater than the min phase time but less than the travel time separation between frontage roads.  Typically, you will set the split times for Ø12 and Ø16 at their minimum value (number in parenthesis) and vary the total frontage road times with Ø4 and Ø8.  The value in parenthesis next to the label, extension Ø12 (5) suggests a safe value of 5" to use for the split for Ø12.

Go ahead and code Split Table# 2 as shown below. For this example, apply a MIN recall instead of a MAX recall to Ø2 and Ø6. Now, force the controller into Pattern# 2, using the TEST mode (MM->2->1).


MM->2->7->2: Split Table #2 (4-Phase Example With Ø2 and Ø6 set to MIN)

Pattern# 2 generates the sequence shown below when a MIN recall is applied to the Coord-Ø 2.  With very short Min Grn settings, the controller is allowed to reservice Ø1 before servicing Ø4. This operation is not what you want for 4P (4-phase) coordination.

If you set the RetHold for Ø2 (MM->2->5, right menu), you can hold Ø2 until it's force-off and prevent Ø1 from being reserviced. You can also set the MAX mode setting for Ø2 like we did for Pattern# 1, to insure that Ø2 holds until it is force-off.


Pattern #2

Controlling Slack Time in 4-Phase Operation

Slack time is unused split time from the actuated phases when they skip or gap-out due to detection. Being able to control where slack time is assigned is usefull when one approach is greatly over-saturated compared to the other approaches. The capacity of the interchange can often be improved by assigning the Coord-Ø to the most congested phase and letting the controler return as much slack time as possible to that phase.  

The pattern offset can be adjusted to reference the Coord-Ø to the beginning of Ø2, 4, 6 or 8 without changing the relative synchroniztion of the diamond.  However, the phase named as the Coord-Ø should be the most congested approach to allow the controller to move slack time to that phase.

In our last example, we assigned Ø2 as the Coord-Ø and learned that we needed to set MAX or RetHold to hold Ø2 until it's force-off. In affect, all slack time not used by the phases prior to Ø2 was assigned to Ø2.  But what if the northbound approach (Ø8) is the most congested approach for this pattern?  We could just as easily assign the Coord-Ø to Ø8 and adjust our offset to reference the beginning of Ø8 rather than the beginning Ø2.  We could also set Easy Float to ON (see Coordination Modes+ above) to insure that all the slack time from the actuated phases prior to Ø8  is moved to the Coord-Ø.

These concepts will be developed in our next example, Pattern# 3.  Enter the Split Table# 3 as shown below.  In this example, we will reference the Coord-Ø to Ø8 and set a MAX recall for that phase.  Set Ø2 to MIN recall, Ø4 to NON (not recalled - skipped) and Ø6 to MAX recall.

Let's also assume that this pattern was originally developed with the Coord-Ø as Ø2 and a 0" offset.  We would also need to adjust the offset in the pattern table to synchronize the diamond at at different point in the cycle.  Since the 4-phase sequence follows Ø2+4+6+8, you must change  the offset from 0" to 0" + 24" + 8" + 20" =  52" to reference the offset to the beginning of Ø8.  This offset adjustment keeps the diamond synchronized at the original 0" offset referenced to the beginning of Ø2.


MM->2->7->3: Split Table #3 (4-Phase Example With Ø8 as the Coord-Ø)

Force the controller into Pattern# 3 using the TEST mode (MM->2->1). Then observe the Timing Status screen under MM->7->1.  You should make the following observations from this screen:

  1. Ø1 and Ø5 do not have a MIN recall in this pattern like Pattern# 1 and 2.  However, the interior left-turns are still being called and serviced.  The controller actually calls the interior left-turns during 4-phase operation to hold the vehicles entering from Ø2 and Ø6 to insure these movements are progressed through the downstream signals.  This was noted in TecNote 1201 - Texas Diamond Modes in Free Operation.

  2. Ø2 services a min time and gaps out. Ø4 skips. 

  3. The controller stays in Ø6 until it is forced off (Term Fof) because of the MAX setting on Ø6.  This uses up all of the slack time from Ø2 and Ø4 during Ø6.

  4. Even though Ø8 has been designated as the Coord-Ø with a MAX recall setting, it is only timing the 18" split assigned to it because Ø6 has used up all of the slack time from Ø2 and Ø4..

Now, go back to Coord Modes+ (MM->2->1, right menu) and change Easy Float to ON.  Note from the Timing Status display (MM->7->1) that Ø6 is now terminating with a max (Term Max) instead of being forced off (Term Fof).  Ø6 is utilizing all of it's programmed split (20"), but the slack time from Ø2 and Ø4 is being passed to the Coord-Ø  like we want.  This adds an additional 22" of slack time from Ø2 and Ø4 to the beginning of Ø8.  Floating force offs (Easy Float) apply a max time to each non-coordinated phase to limit the phase to the programmed split.  Floating force-offs insure that the slack gets back to the Coord-Ø.  This is a very usefull feature during coordinated diamond operation because often only one approach is over-saturated and you can control which approach gets the slack time by assigning the Coord-Ø on a pattern by pattern basis.

Disabling Frontage Road Extension by Pattern

The default 4-phase operation assumes that frontage road extension phases Ø12 and Ø16 time concurrently with the beginning of Ø2 and Ø6.  In TecNote 1201 - Texas Diamond Modes in Free Operation we learned how to disable Ø12 and Ø16 from MM->1->1->2. However, you may want to leave these phases enabled and disable them by pattern. This will be demonstrated in teh Pattern# 4 example below

Program Split Table# 4 and run Pattern# 4 under TEST mode. Observe that Ø12 and Ø16 are disabled when this Split Table# 4 is in effect because of the OMT values programmed in the Mode settings for these phases.


MM->2->7->4 (left menu): Pattern# 4 - MAX applied to Coord-Ø, Ø6


MM->2->7->4 (right menu): OMT Applied to Ø12 and Ø16 Disables Front Rd. Extension

Key Points Related to 4-Phase Diamond Mode Coordination

  1. Diamond coordination is programmed using the EASY force-off method of coordination. Set the Force-off value to OTHER and Force-off+ to EASY to enable this mode.

  2. The travel time between frontage roads limits how long you can extend the frontage roads concurrently with the beginning of Ø2 and Ø6.  You may omit (OMT) the frontage road extension phases Ø2 and Ø6 in the split table if the travel time is less than the min times of the frontage road extension phases (Ø12 and Ø16).

  3. Use as much shortway as practical for each pattern, but exclude Ø4, 8, 12 and 16 from shortway for 4-phase coordination.  This helps keep Ø4+12 and Ø8+16 as short as possible.

  4. The diamond coordination spreadsheet allows you to specify the cycle length and the split times for each approach enterning the diamond (Ø2+4+6+8) and performs most of coord diagnostics in the controller for you.

  5. The offset is always referenced to the beginning of the Coord-Ø.  Specifying Offset EndGRN under MM->2->5 (right menu) has no effect on the offset reference.  The EASY coordination method always references the offset to the beginning of the Coord-Ø.

  6. You can specify any phase in the sequence (Ø2+4+6+8) as the Coord-Ø.  However, you should place a MAX recall in the split table or apply a RetHold to the pattern to insure that any unused slack time returns to that phase.  You may also set Easy Float to ON to insure that all slack time is passed to the Coord-Ø.

3-Phase Diamond Mode Coordination

3P (3-phase) coordination allows the arterial phases to time concurrently followed by dual lagging left-turns and the frontage road interval.  The lagging left-turns drive the interior overlaps of the diamond clearing any vehicles within the interior of the interchange prior to the frontage roads being serviced. 

3P (3-phase) coordination is somewhat limited in that the frontage road phases must begin together and end together even if only one frontage road is extended by detection. This operation works relatively well if the split times for both frontage roads are approximately equal.  When the demand from one frontage road is drastically different from the other frontage road and 4P (3-phase) operation is not feasible, then Sep (Separate intersection) mode should be considered.

If a frontage road is skipped, the controller dynamically inserts Ø10 or Ø14 to clear the interior of the diamond as was shown in TecNote 1201 - Texas Diamond Modes in Free Operation. This skip feature is also available under 3-phase diamond coordination.

The following examples will illustrate these points.  Enter the following values into the spreadsheet (tab III. 3 Phase Operation) and update Split Table# 5 as shown below.


MM->2->7->5 (left menu): Pattern# 5 - 3-Phase Coordination


MM->2->7->5 (right menu): Pattern# 5 - 3-Phase Coordination

Force the controller to run Pattern# 5 in TEST mode.  Observe the Timing Status screen (MM->7->1) and insure that Seq 98 and 3Ø are active under coordination.  Note that 2+6, 1+5 and 4+8 are timing together because their split times are equal.  Also, confirm that Ø2 and Ø6 are servicing a MAX recall and 1, 4, 5, and 8 are being serviced with a MIN recall.

Go back to Split Table# 5 and change the Mode for Ø4 from MIN to MAX. From the status display, observe that Ø4 and Ø8 still begin together and end together in the sequence even though only Ø4 is being extended past it's minimum with the max call.

Now change the Mode for Ø4 in Split Table# 5 from MAX to NON.  The controller inserts Ø10 when Ø4 is skipped, just like free operation. Ø10 drives overlap 2 to clear the interior of the diamond downstream of Ø4.

Try to change the frontage road splits in the spreadsheet so that they are unequal.  You will get a message "Error - Frontage Road Splits Must Be Equal".  Try running uneven frontage road splits in Split Table# 5 as shown below:


MM->2->7->5: Pattern# 5 - Uneven Split Times for Frontage Roads Ø4 and Ø8

If you look at the coord diagnostics (MM->2->8->5), you will see that this pattern fails with a BARRIER ERR.  You cannot specify different split times for the frontage road phases because Ø4 and Ø8 are not concurrent with Ø1, 2, 5 and 6.  Therefore, under 3P (3-phase) coordination, the frontage road splits must be equal.  However, we can make the split times for Ø2 and Ø6 different under 3P (3-phase) coordination as we will see in our next example.

Modify Split Table# 6 as shown. Program phases 9-16 like those shown above for Split Table# 5. 


MM->2->7->6: Pattern# 6 - Uneven Split Times for Ø2 and Ø6

Force the controller into Pattern# 6 using the TEST mode (MM->2->1). Confirm that your coord diagnostics did not generate an error for this example.  The sum of each ring (ring1=Ø1-4 and ring2=Ø5-8) equals the cycle length and the barriers cross at the same point, so the diagnostics indicate Pattern#6 is OK..

Because Ø6 ends 5" before Ø2, Ø5 begins 5" before Ø1.  However,  Ø1 and Ø5 must still end together to cross the barrier to Ø4 and Ø8.

Change the Mode setting for Ø1 from MAX to NON and note that Ø1 and Ø5 are both serviced even though one phase is called.  This is because there are calls on both frontage roads and the controller always services the interior left-turns to clear the interior of the diamond before servicing the frontage roads.  If you take the MAX call off both frontage roads and only call one left-turn phase is called, then the other left-turn will not be serviced.

The only way to understand the logic applied to 3P (3-phase) coordination is to play with these examples looking at the controller response when detection is varied.  3P (3-phase) coordination is restricted by the common barrier between both rings; however when capacity requirements are approximately equal on both frontage roads, the operation works quite well.  However, when the frontage road spacing is great enough that 3P (3-phase) is preferred over 4P (4-phase) operation and the frontage road splits are drastically different, you need to consider Sep (Separate Intersection) mode.

Sep (Separate Intersection) Diamond Mode Coordination

Sep (Separate intersection) mode overcomes the barrier restriction between the phases in ring 1 and ring 2 with 3P (3-phase) coordination.  This provides the ability to run different split times for the frontage roads. The other primary difference is that 3P (3-phase) lags the interior left-turns at the diamond where Sep (Separate intersection) mode runs both interior left turns leading. 

However, we will see in the examples below that Sep (Separate intersection) coordination is very dependent on the Coord-Ø selected for the pattern, because the Coord-Ø determines the synch point for the other ring.

Enter the following Sep (Separate intersection) example as Split Table# 7 and force Pattern# 7 into TEST mode.


MM->2->7->7: Pattern# 7 - Sep Mode, Coord-Ø 2, Uneven Frontage Road Splits

Sep (Separate intersection) mode, like all coordination modes, references the offset to the begining of the Coord-Ø.  However, because there are no barriers in this mode, the controller applies a set of rules to synchronize the other ring.  In our current example, the Coord-Ø is set to Ø2.  This sychronizes the beginning of Ø2 and the beginning of Ø8 to the pattern offset as shown below. 

Note from this example that Sep (Separate intersection) mode unlike 3P (3-phase) mode does not require the frontage road splits (Ø4 and Ø8) to be equal.  Also, recall that the frontage road signals are driven by overlaps; however, because Ø9-16 are omitted in Sep (Separate intersection) mode, these overlaps are actually driven by Ø4 and Ø8.

Force the controller into Pattern# 7 and observe the following operation with the Coord-Ø set to Ø2.  Note on the Phase Timing display that the offset hits at Loc=0 at the beginning of Ø2 and Ø8.

  

Now, move the coord phase in Split Table# 7 from  Ø2 to Ø4 and observe the following operation.  This synchs the the beginning of Ø8 to the Coord-Ø4 in ring 1.  This operation is very similar to 3P (3-phase) coordination because Ø4 and Ø8 begin together.  However, the frontage road phases (Ø4 and Ø8) do not have to end together if their split times are not equal. Moreover, the left-turns are not lagging as in 3P (3-phase) coordination, so there is no clearance interval to "flush" the interior of the diamond before the frontage roads are serviced.

  

Finally, move the coord phase in Split Table# 7 from  Ø4 to Ø1 and observe the following. 

 

Setting the Coord-Ø to Ø1 allows the arterial and frontage road movements to clear the downstream signals when the phase splits are approximately equal to the start-up travel time between the frontage roads.

Diamond Coordination in USER Phase Mode

Naztec has recently developed an enhanced NTCIP coordination method (using FIXED or FLOAT force-offs) to coordinate the diamond in USER phase mode.  This method applies a separate lag offset to each ring (for rings 2-4) to make the coordination in each ring totally independent.  Since NTCIP requires one Coord-Ø and one offset per pattern, the pattern offset is referenced to the Coord-Ø in ring 1. Rings 2-4 may have separate lag offsets to reference a Coord-Ø in each ring.  The synchronization of each ring is totally independent. This allows the controller to run all of the 3-phase lead/lag diamond sequences currently modeled in PASSER III. 

Providing separate offsets to a separate Coord-Ø in each ring provides the same operation as 4 independent single ring controllers running a common cycle length.  This feature also makes it possible to define 2 independent dual ring controllers within 4 rings with each controller having it's own offset.

Some Final Words About the Spreadsheet

These comments are fine points not presented above.  The spreadsheet was designed to make programming diamond coordination as simple as possible.  However, there were some assumptions used to develop the spreadhseet that you should be aware of.

The clearance times for the frontage roads may be programmed as overlap settings.  For example, the Yellow and Red timing for Overlap 11 under MM->1->5->2->11->1 may be used to specify clearance times that differ from the included phase that terminates the overlap (in this case Ø12).  However, the spreadsheet assumes that "Parent Ø Clearance" under MM->1->5->1 has been set to ON and that the overlaps time the clearance times of the phases terminating the overlap.

The spreadsheet will generate a warning message if any phase yellow clearance time is less than 3" as required by the MUTCD. If your interchange always runs 4P (4-phase) operation with frontage road extensions (Ø12 and Ø16), then you can reduce the minimum split for the frontage road by reducing the yellow clearance times for Ø4 and Ø8 below 3" because these clearance times are never applied to the overlap clearances.  You must set Unit Parameter, Allow <3 sec Yel to ON under MM->1->2->1 in order to set the yellow clearance less than 3".

Conclusion

This TecNote serves as a primer to introduce you with the various Texas Diamond Modes running coordination. In addition a spreadsheet is provided to help you develop split times that will pass the coordination diagnostics in the version 50/60 controllers.

A good reference to help you understand diamond operation is Texas Transportation Institute Publication TX-00/4913-1, "COORDINATION OF DIAMOND INTERCHANGES WITH ADJACENT TRAFFIC SIGNALS", October 2000 (click here and search on "4913-1").