5-PHASE SINGLE LAG 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:
SINGLE LAG WITH ALL-RED TURN CLEARANCE
The diagram below shows the phase sequence of traffic flow for a single lag with all-red clear (quick animation).
The diagram on the right shows the signal display sequence used (slow animation to show clearance intervals).
SINGLE LAG PHASE ORDER
The single lag sequence with red clear normally operates in the following manner:
- Assuming traffic is waiting to use them, the straight-ahead phase 1 and the overlap phase A on the main street operate first.
- When the straight-ahead phase runs out of traffic, both straight-ahead phases end with clearance periods, and the red clear period begins.
- After the red clear period finishes, the lag left-turn phase 3 and the overlap phase A begin.
- When the lag phase runs out of traffic, the lag and overlap phases terminate with simultaneous clearance periods.
- The side street phase has its period.
Parts of the above sequence can be omitted. For example, the street could start with the left turn and the adjacent straight-ahead movement.
Thus, the yellow-trap hazard can not occur.
The numbers on the diagram are phase numbers.
(1 A)
(2)
(3 A)
(4)
SINGLE LAG WITH ALL-RED TURN CLEARANCE
- This is used with either the 3-light protected or the 5-light protected/permissive left-turn display (see diagrams at right). Because the trapped left turn does not have a left turn phase, the display type does not matter.
- 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, a different phase order is needed. Dummy phases are used.
- This sequence will prevent yellow-trap.
| 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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ALL-RED TURN CLEARANCE
The phase order of a single-ring controller is shown. The quad left-turn sequence and dual-ring controller are explained here.
In all-red-turn clearance, an extra phase with nothing but all-red clearance timing is needed.
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.
Because a single ring is used, no barriers are used.
| PHASE TABLE | ||||
|---|---|---|---|---|
| Timing Rings: | TR-1 (1 2 3 4) | TR-2 () | ||
| Concurrency: | CG-1 (1 2 3 4) | |||
| Timing groups: | TG-1 (1) | TG-2 (2) | TG-3 (3) | TG-4 (4 7) |
| Overlap pairs: | none | |||
| EXTRA OVERLAP PHASE TABLE | ||||
|---|---|---|---|---|
| Overlap unit | Parent phases | Conditions | ||
| OV-A | (1 3) | |||
| OV-B | - | |||
| OV-C | - | |||
| OV-D | - | |||
| PHASE DIAGRAM | ||||||||
|---|---|---|---|---|---|---|---|---|
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| TG-1 |  Phase 1 |
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| TG-2 |  Phase 2 |
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| TG-3 |  Phase 3 |
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OV-A |
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| TG-4 |  Phase 4 |
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INTERFACING THE INTERSECTION
ALL-RED TURNS CLEARANCE
| DETECTOR | ||||
|---|---|---|---|---|
| Detector | Normal phase |
Redirect phase | Redirect when | |
| 1 | 1 | - | ||
| 2 | 1 | 3 | Phase 3 active (optional) | |
| 3 | 3, call 2 | - | ||
| 4 | 4 | - | ||
| - | - | |||
| - | - | |||
| - | - | |||
| - | - | |||
| SIGNAL FACE TABLE | ||||
|---|---|---|---|---|
| Face | Phase | Modifier | ||
| 1 | 1 | |||
| 2 | 2 | No load switch or signal face. | ||
| 3 | 3 | No red indication (phase A in same face) | ||
| 4 | 4 | |||
| - | ||||
| - | ||||
| - | ||||
| - | ||||
| A | OV-A | |||
| INTERSECTION DIAGRAM | ||||||||
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1 | 1 | |
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|3|A| | |A| | |
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4 | |4| | |
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|4| | 4 |  |
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|1| | |1| | |
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3(2) | 1(3) | |
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Detectors are blue. Signal faces are orange.
Calls and redirects are in parentheses.
SINGLE LAG WITH ALL-RED TURNS CLEAR
ADVANTAGES
- Allows the safe use of a lag left-turn phase.
- Phase skip partially prevents wasting time at empty approaches.
- Can be used at a simultaneous node in a progression system.
- Can not yellow-trap.
SINGLE LAG WITH ALL-RED TURNS 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.
- A completely different controller setup is needed for each different phase pattern.
- The red clear wastes intersection time.