An evaluation of five-section protected/permitted left-turn signal displays using advanced driving simulator technology

Abstract

One relatively new type of left-turn signal phasing designed to minimize the protected left-turn phase time requirements, while increasing the opportunity for left-turn maneuvers, is protected/permitted left-turn (PPLT) phasing. PPLT signal phasing provides a protected phase for left-turns as well as a permitted phase during which left-turns can be made if gaps in opposing traffic allow, all within the same signal cycle. Consequently PPLT signal phasing can improve operational efficiency by increasing left-turn capacity and reducing delay at signalized intersections. The positive attributes of PPLT phasing are presented to the driver through the use of traffic signal displays. Traffic signal displays illuminate circular- and arrow-shaped indications to allow different traffic maneuvers through the intersection. The meaning of each indication is transmitted to the driver by its color, shape, orientation, and position within the traffic signal display. The Manual on Uniform Traffic Control Devices (MUTCD) is the current source of guidelines on the use of traffic signal displays. According to the MUTCD, proper use of traffic signal displays can improve the overall capacity, efficiency, and safety of an intersection.