Use of protected/permitted left-turn signal control in the U.S.

Abstract

The growing level of traffic demand on urban and rural roadways has led to increased use of protected/permitted left-turn (PPLT) signal control. PPLT signal phasing provides an exclusive phase for left turns as well as a permissive phase during which left turns can be made if gaps in opposing through traffic allow, all within the same signal cycle. The signal display most commonly used with PPLT signal phasing is a five-section signal display with a green arrow indication for the exclusive left-turn phase and a green ball for the permitted left-turn phase. However, many transportation agencies use different mounting locations, signal display arrangements, and permitted indications when implementing PPLT. In addition, there are at least four variations of the permitted indication, including the flashing red ball, flashing red arrow, flashing yellow ball, and flashing yellow arrow. This paper presents the results of a comprehensive agency survey sent to local, county, and state officials designed to determine the use of PPLT signal control in the United States. The first section presents general survey information, including the total number of surveys received and the total number of signalized intersections reported. This section also quantifies the number of signalized intersections containing PPLT signal displays. The second section presents the types of PPLT signal displays used by these agencies and typical signal display mounting practices. The third section presents intersection geometry and signal phasing practices most often used with PPLT signal phasing. Finally, the last section provides a brief summary of the results.