8-PHASE QUAD LEFT WITH FALSE CALL PLACEMENT
THIS SEQUENCE PLACES FALSE CALLS TO PREVENT YELLOW-TRAP
When a left turn detector places a call, it also places a false call to the calling detector input on the highest-volume cross street phase. But since the call is on the calling detector, it can't extend the green on the cross street phase. This sequence causes calls to left-turn phases on a given street to provide their own protection by calling a cross-street phase. Yellow-trap cannot occur with this sequence. However, it will not work with any phase order except split lead.
How false call placement works:
QUAD LEFT WITH FALSE CALL PLACEMENT
The diagram on the right shows a quad split lead with left turns causing the cross-street phases to become active before the left turn calls are answered.
QUAD LEFT-TURN PHASE ORDER
The quad left-turn sequence (quad split lead) normally operates in the following manner:
- Assuming traffic is waiting to use them, both left-turn phases on one street operate first.
- When one left-turn phase runs out of traffic, it ends with clearance periods, and the oncoming straight-ahead phase is released.
- When the other left-turn phase runs out of traffic, it also ends with clearance periods, and the oncoming straight-ahead phase is released. Now both straight-ahead phases are moving traffic.
- When both straight-ahead phases run out of traffic, they terminate with simultaneous clearance periods.
- The same sequence then occurs on the other street.
If some of the approaches or phases have no traffic on them, those phases can be skipped. This can cause the following effects:
- Parts of the above sequence can be omitted. For example, the street could start with one left turn and the adjacent straight-ahead movement, or even both straight-ahead movements.
- If one entire street has no traffic waiting, the left turn phase places a false call to activate it. Thus, the yellow-trap hazard can not occur.
The numbers on the diagram are phase numbers.
(1 5)
(1 6) ||||| (2 5)
(2 6)
(3 7)
(4 7) ||||| (3 8)
(4 8)
QUAD LEFT WITH FALSE CALLS
- This is used with the 5-light protected/permissive left-turn display (see diagrams at right). A signal with all 3-light left-turn signals does not need this sequence unless some approaches don't have left turn phases.
- All signal faces are standard.
- The circular aspects of the 5-light signal display the same aspects as the adjacent straight-ahead signals.
- The wiring for this system is standardized.
- The MUTCD (Manual of Uniform Traffic Control Devices) prescribes this basic kind of display.
- With False Calls, the protected/permissive version has protection against yellow-trap from phase skip
| Signal faces used with this method | |
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| Standard 3-light signal face for left turns that are always protected. Not used with this method: |
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| Standard 5-light signal face for left turns that are both permissive and protected: |
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| Standard 3-light signal for completely permissive left turns oncoming to either of the above displays: |
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| Standard signal for all straight-ahead indications, and left turns on streets without left-turn phases: |
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FALSE CALL PLACEMENT
The phase order of a dual-ring controller is shown. The quad left-turn sequence and dual-ring controller are explained here.
In false call placement, each left turn detector also calls a phase on the cross street, but without the ability to extend the green on that cross street phase.
The false call thus causes the cross street green to display for a short period before the left turn phases become active.
False Calls makes the timers advance out of the straight-ahead phases to phases on the other street. Only after that happens can the left turn phases be active again.
| PHASE TABLE | ||||
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| Timing Rings: | TR-1 (1 2 3 4) | TR-2 (5 6 7 8) | ||
| Concurrency: | CG-1 (1 2 5 6) | CG-2 (3 4 7 8) | ||
| Timing groups: | TG-1 (1 5) | TG-2 (2 6) | TG-3 (3 7) | TG-4 (4 8) |
| Overlap pairs: | (1 5) | (1 6) | (2 5) | (2 6) |
| Overlap pairs: | (3 7) | (3 8) | (4 7) | (4 8) |
| EXTRA OVERLAP PHASE TABLE | ||||
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| Overlap unit | Parent phases | Conditions | ||
| OV-A | - | |||
| OV-B | - | |||
| OV-C | - | |||
| OV-D | - | |||
| PHASE DIAGRAM | ||||||||
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Ring 2 |
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| TG-1 |  Phase 1 |
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 Phase 5 |
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| TG-2 |  Phase 2 |
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 Phase 6 |
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BARRIER | |
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BARRIER |
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| TG-3 |  Phase 3 |
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 Phase 7 |
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| TG-4 |  Phase 4 |
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BARRIER | |
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BARRIER | |
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INTERFACING THE INTERSECTION
FALSE CALL PLACEMENT
| DETECTOR | ||||
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| Detector | Normal phase |
Redirect phase | Redirect when | |
| 1 | 1, call 4 | - | ||
| 2 | 2 | - | ||
| 3 | 3, call 6 | - | ||
| 4 | 4 | - | ||
| 5 | 5, call 4 | - | ||
| 6 | 6 | - | ||
| 7 | 7, call 6 | - | ||
| 8 | 8 | - | ||
| SIGNAL FACE TABLE | ||||
|---|---|---|---|---|
| Face | Phase | Modifier | ||
| 1 | 1 | No red indication (phase 6 in same face) | ||
| 2 | 2 | |||
| 3 | 3 | No red indication (phase 8 in same face) | ||
| 4 | 4 | |||
| 5 | 5 | No red indication (phase 2 in same face) | ||
| 6 | 6 | |||
| 7 | 7 | No red indication (phase 4 in same face) | ||
| 8 | 8 | |||
| INTERSECTION DIAGRAM | ||||||||
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6 | 1(4) |  |
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|5|2| | |2| | |
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7(6) | |8| |3| |
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|7| |4| |
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4 | |
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|6| | |6|1| | |
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5(4) | 2 | |
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Detectors are blue. Signal faces are orange.
False calls are in parentheses.
QUAD WITH FALSE CALL
ADVANTAGES
- Maximizes time use at isolated intersection.
- Phase skip partially prevents wasting time at empty approaches.
- Conforms to driver expectation of phase sequence.
- Can be used at a simultaneous node in a progression system.
- Easy to connect.
- Can not yellow-trap.
QUAD WITH FALSE CALL
DISADVANTAGES
- The order of phases can not be altered to make other sequences without causing yellow-trap.
- Can not be used away from a simultaneous node in a progression system.
- The false calls waste intersection time.