30 Jun Protected-Permitted Left-turn Phasing Study and Design (City of Petaluma)
Protected-permitted left-turn phasing was installed by former City staff at a number of intersections in the City of Petaluma without benefit of analysis to determine its suitability. To address complaints about its functionality at some locations, W-Trans was hired to evaluate 26 intersections to determine if the phasing should remain or be replaced with either permitted only or protected left-turn phasing. The evaluation included a review of several key factors, including the collision history (particularly left-turn related), lane configuration, sight lines, vehicle speed and traffic volumes. An evaluation matrix was developed with City staff that was used to determine if changes were needed. ‘Abbreviated’ design plans were then prepared focusing on signal head equipment modifications. For some intersections all or some of the protected-permitted phasing was retained, though the installation was modified to include the newly approved flashing yellow arrow indications. At the remaining intersections the protected-permitted indications were removed and replaced with arrow or ball indications. W-Trans provided construction assistance to modify the traffic signal controller cabinets, provide timing sheets, and conflict monitor breakout diagrams.