10-PHASE QUAD LEFT WITH ALL-RED TURN CLEARANCE
THIS SEQUENCE PLACES AN ALL-RED CLEARANCE BEFORE A LAG TURN PHASE
When simultaneous straight-ahead phases are displayed, both phases must terminate together. Then, an all-red period precedes any lag left-turn phase and its concurrent phases. This clears the cars waiting to turn on the circular green before the lag phase starts. Yellow-trap cannot occur with this sequence. It will work with any phase order.
How all-red turn clearance works:
QUAD LEFT WITH ALL-RED TURN CLEARANCE
The diagram on the right shows a quad split lead with all-red clear after simultaneous straight-ahead phases.
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, an all-red-clearance phase occurs alone in its place. Thus, the yellow-trap hazard can not occur.
The numbers on the diagram are phase numbers.
(1 5)
(1 6) ||||| (2 5)
(2 6) ||||| ( 9 )
(3 7)
(4 7) ||||| (3 8)
(4 8) ||||| ( 10)
QUAD LEFT WITH ALL-RED TURN CLEARANCE
- 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 all-red turn clearance, the phase unit must be modified or programmable.
- This sequence will prevent yellow-trap.
| Signal faces used with this method | |
|---|---|
| Standard 3-light signal face for left turns that are always protected. Not used with this method: |
|
| Standard 5-light signal face for left turns that are both permissive and protected: |
|
| Standard 3-light signal for completely permissive left turns oncoming to either of the above displays: |
|
| Standard signal for all straight-ahead indications, and left turns on streets without left-turn phases: |
|
ALL-RED TURN CLEARANCE
The phase order of a dual-ring controller is shown. The quad left-turn sequence and dual-ring controller are explained here.
In all-red-turn clearance, two extra phases with nothing but all-red clearance timing are needed. This requires a special controller.
The red clearance causes both sides to turn yellow at the same time. Then, after the red clearance, the lag left turn and its concurrent phase can becomes active.
All-red turn clearance requires the controller to cross the barrier in an all-red state before it cycles to a left turn phase.
| PHASE TABLE | ||||
|---|---|---|---|---|
| Timing Rings: | TR-1 (1 2 3 4) | TR-2 (5 6 7 8 9 10) | ||
| Concurrency: | CG-1 (1 2 5 6) | CG-2 (9) | ||
| Concurrency: | CG-3 (3 4 7 8) | CG-4 (10) | ||
| Timing groups: | TG-1 (1 5) | TG-2 (2 6) | TG-3 (9) | |
| Timing groups: | TG-4 (3 7) | TG-5 (4 8) | TG-3 (10) | |
| Overlap pairs: | (1 5) | (1 6) | (2 5) | (2 6) |
| Overlap pairs: | (3 7) | (3 8) | (4 7) | (4 8) |
| EXTRA OVERLAP PHASE TABLE | ||||
|---|---|---|---|---|
| Overlap unit | Parent phases | Conditions | ||
| OV-A | - | |||
| OV-B | - | |||
| OV-C | - | |||
| OV-D | - | |||
| PHASE DIAGRAM | ||||||||
|---|---|---|---|---|---|---|---|---|
| |
Ring 1 |
|
 |
|
Ring 2 |
|
|
|
| |
|
|
|
|
|
|||
| TG-1 |  Phase 1 |
|
|
 Phase 5 |
|
|
||
| | CG-1 | |
|
|
|
||||
| TG-2 |  Phase 2 |
|
|
 Phase 6 |
|
|
||
| |
|
|
|
|
|
|||
| |
BARRIER | |
|
|
|
|
|
|
| TG-3 CG-2 |
|
|
|
|
Phase 9 | |
|
|
| |
BARRIER | |
|
|
|
|
|
|
| |
|
|
|
|
|
|||
| TG-4 |  Phase 3 |
|
|
 Phase 7 |
|
|
||
| | CG-3 | |
|
|
|
||||
| TG-5 |  Phase 4 |
|
|
 Phase 8 |
|
|
||
| |
|
|
|
|
|
|||
| |
BARRIER | |
|
|
|
|
|
|
| TG-6 CG-4 |
|
|
|
|
Phase 10 | |
|
|
| |
BARRIER | |
|
|
|
|
|
|
| |
|
|
|
|
|
|
|
|
INTERFACING THE INTERSECTION
ALL-RED TURN CLEARANCE
| DETECTOR | ||||
|---|---|---|---|---|
| Detector | Normal phase |
Redirect phase | Redirect when | |
| 1 | 1, call 9 | - | ||
| 2 | 2 | - | ||
| 3 | 3, call 10 | - | ||
| 4 | 4 | - | ||
| 5 | 5, call 9 | - | ||
| 6 | 6 | - | ||
| 7 | 7, call 10 | - | ||
| 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 | ||||||||
|---|---|---|---|---|---|---|---|---|
| |
|
|
|
|
|
|
|
|
| |
|
|
|
|
 |
|
|
|
| |
|
|
6 | 1(9) |  |
|
|
|
| |
|
|
|
|5|2| | |2| | |
|
|
 |
|
|8| | |
|
|
|
8 | |
| |
7(10) | |8| |3| |
|
|
|
|7| |4| |
3(10) | |
| |
4 | |
|
|
|
|4| | |
 |
| |
|
|
|6| | |6|1| | |
|
|
|
| |
|
|
|
5(9) | 2 | |
|
|
| |
|
|
 |
|
|
|
|
|
| |
|
|
|
|
|
|
|
|
Detectors are blue. Signal faces are orange.
Calls to dummy phases are in parentheses.
QUAD WITH ALL-RED TURN CLEAR
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 not yellow-trap.
QUAD WITH ALL-RED TURN CLEAR
DISADVANTAGES
- The order of phases can be altered to make other sequences without causing yellow-trap. But it can't do lead-lag very well.
- Can not be used away from a simultaneous node in a progression system because it divides the green period.
- The red clears waste intersection time.
- Requires a special signal controller.