Dallas PPLT Displays (Horizontal Head) - Lead Left-turn
Dallas and Arlington Phasing were developed to overcome the "yellow-trap" safety problem when lead/lag left-turn phasing is used with protected/permitted left-turn displays. The "yellow trap" condition applies for only the lead left-turn display (not the lag left-turn display). The "yellow trap" results when the permitted indications in the lead left-turn display are the same as the circular displays in the adjacent signal thru head when both displays are clearing to the lag left-turn as shown below.
Dallas Phasing solves the "yellow-trap" safety problem for the leading left-turn driver by holding a solid green indication in the left-turn signal head during the opposing lag left-turn interval. Louvers are used to shield the left-turn display so the green display in the left-turn signal cannot be easily seen by thru divers approaching the intersection.
The permitted (circular) signal indications in the Dallas Phasing display are driven by an overlap defined from the left-turn and through phases so that the overlap remains green until end of the lagging left-turn interval when the right-of-way is transferred to the intersecting street.
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