The safety impacts of left-turn phasing sequence have long been a discussion topic for traffic engineers. This research investigated the safety impacts of different types of left-turn signal phasing sequence under different types of left-turn signal control modes. It was found that, under protected-only (PO) control mode, lead-lag is the safest sequence, followed by the lead-lead and lag-lag sequences; under protected/permissive left-turn (PPLT) control mode, the lead-lead sequence is safer than the lead-lag sequence. In addition, the safety impacts of consistency of signal phasing were assessed by comparing the accident rates at four different corridor sections with different levels of mixed signal phasing sequences. It was found that the application of mixed signal phasing sequences increased the risk of accidents at intersections.
Abstract