SINGLE LEAD LEFT WITH FALSE CALL PLACEMENT
THIS SEQUENCE PLACES FALSE CALLS TO PREVENT YELLOW-TRAP
When the 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:
SINGLE LEAD WITH FALSE CALL PLACEMENT
The diagram on the right shows a single lead with left turns causing the cross-street phase to become active before the left turn calls are answered.
SINGLE LEAD PHASE ORDER
The single lead left-turn sequence normally operates in the following manner:
- Assuming traffic is waiting to use them, the left-turn phase operates first, with the concurrent straight-ahead phase.
- When the left-turn phase runs out of traffic, it 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 cross-street phase then operates.
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 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.
(2 5)
(2 6)
(4)
SINGLE LEAD WITH FALSE CALLS
- This is used with the 5-light protected/permissive left-turn display or the 3-light protected left-turn signal.
- 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: |
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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, the 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 (2 4) | TR-2 (5 6) | ||
| Concurrency: | CG-1 (2 5 6) | CG-2 (4) | ||
| Timing groups: | TG-1 (5) | TG-2 (2 6) | TG-3 (4) | |
| Overlap pairs: | (2 5) | (2 6) | ||
| 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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| TG-2 |  Phase 2 |
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BARRIER | |
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BARRIER |
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| TG-3 |  Phase 4 |
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BARRIER | |
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BARRIER | |
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INTERFACING THE INTERSECTION
FALSE CALL PLACEMENT
| DETECTOR | ||||
|---|---|---|---|---|
| Detector | Normal phase |
Redirect phase | Redirect when | |
| - | - | |||
| 2 | 2 | - | ||
| - | - | |||
| 4 | 4 | - | ||
| 5 | 5, call 4 | - | ||
| 6 | 6 | - | ||
| - | - | |||
| - | - | |||
| SIGNAL FACE TABLE | ||||
|---|---|---|---|---|
| Face | Phase | Modifier | ||
| - | ||||
| 2 | 2 | |||
| - | ||||
| 4 | 4 | |||
| 5 | 5 | No red indication (phase 2 in same face) | ||
| 6 | 6 | |||
| - | ||||
| - | ||||
| INTERSECTION DIAGRAM | ||||||||
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6 | 6 |  |
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|5|2| | |2| | |
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4 | |4| | |
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|4| | 4 |  |
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|6| | |6| | |
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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.
- Can be used away from a simultaneous node in a progression system on the lead side.
- 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.
- The false calls waste intersection time.