Protected–permissive left turn phasing with flashing yellow arrow signal: study of red intervals for an effective phase transition

Abstract

Protected–permissive left turn (PPLT) phasing has been popular and widely used in many urban intersections in North America because of its operational benefits. A significant number of intersections have recently been upgraded with four-section signal heads with flashing yellow arrow (FYA) indication for an effective protected–permissive left turn operation. The present study seeks to find appropriate length of two red intervals whose roles are important, but different during the transition period of FYA-PPLT phasing. One is a red interval for delayed-start of permissive left turn movements; the other is additional red interval for delayed-start of opposing through movements. Micro-traffic simulation and conflict analysis are explored to assess the effects of the red intervals on intersection efficiency and safety. A useful reference, which describes the balanced length of the two red intervals under varying traffic levels, is developed as a result.