8-PHASE QUAD LEFT WITH DETECTOR REDIRECTTHIS SEQUENCE REDIRECTS DETECTORS TO PREVENT YELLOW-TRAPWhen both straight-ahead phases are active, this sequence causes calls to left-turn phases on a given street to extend the straight-ahead phases instead of calling the left-turn phases. Yellow-trap cannot occur with this sequence. However, it will not work with any phase order except split lead. How detector redirection works: | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
QUAD LEFT WITH REDIRECTED DETECTORSThe diagram on the right shows a quad split lead with left turns allowed only after the cross street phases are active. |
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QUAD LEFT-TURN PHASE ORDERThe quad left-turn sequence (quad split lead) normally operates in the following manner:
If some of the approaches or phases have no traffic on them, those phases can be skipped. This can cause the following effects:
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 REDIRECTION
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DETECTOR REDIRECTIONThe phase order of a dual-ring controller is shown. The quad left-turn sequence and dual-ring controller are explained here. In detector redirection, each left turn detector is redirected away from its left turn phase and toward the adjacent straight-ahead phase whenever the oncoming straight-ahead phase is active (green, yellow, or red clear). The detector redirection causes the left turn detectors to extend the adjacent straight ahead green instead of calling the left turn phases. Detector redirection prevents the timers from advancing out of the straight-ahead phases, unless a call is placed on the other street, and the controller actually cycles to a phase on the other street. Only then can the left turn phases be actuated again.
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INTERFACING THE INTERSECTION
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DETECTOR | ||||
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Detector | Normal phase |
Redirect phase | Redirect when | |
1 | 1 | 6 | phase 2 active | |
2 | 2 | - | ||
3 | 3 | 8 | phase 4 active | |
4 | 4 | - | ||
5 | 5 | 2 | phase 6 active | |
6 | 6 | - | ||
7 | 7 | 4 | phase 8 active | |
8 | 8 | - |
SIGNAL FACE TABLE | ||||
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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(6) | |
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|5|2| | |2| | |
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|8| | |
8 | |||||
7(4) | |8| |3| |
|7| |4| |
3(8) | |||||
4 | |
|4| | |
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|6| | |6|1| | |
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5(2) | 2 | |
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Detectors are blue. Signal faces are orange.
Redirected calls are in parentheses.
Links: