GUIDELINES FOR SELECTING TYPE OF LEFT-TURN PHASING

Abstract

At the present time, there is no uniform method of application of left-turn signal phasing throughout the United States. Different jurisdictions use different approaches to determine which type of left-turn phasing--permissive, exclusive, or exclusive/permissive--should be used. Guidelines for selecting the appropriate type of left-turn signal phasing are presented. The guidelines are based on the effect of different types of phasing on left-turn delay, through delay, and safe intersection operation. The effect of different types of left-turn phasing on left-turn and through delay was determined from observing six arterial-arterial intersections. Time-lapse photography was used to observe volume, number of vehicles stopping, total delay, average delay per stopped vehicle, and average delay for all approach vehicles for each turning movement. The guidelines presented select the type of left-turn phasing based on left-turn volume, opposing volume, number of opposing lanes, cycle length, approach speed, sight distance restrictions, and accident history.