A simulation study of the operational performance of left-turn phasing and indication sequences

In this paper, the operational performance of left-turn phasing and indication sequence is presented. The study contributes to the selection of an optimal left-turn phasing and indication sequence. Presently, there are no comprehensive guidelines to assist traffic engineers in this task. The operational performance of six different phase patterns and three intersection geometries are addressed using simulations. The threshold values to identify traffic conditions under which each phase pattern performs best and beyond which another phase pattern should be considered are also formulated. The efficiency of leading and lagging sequences are addressed. The study shows that when some left-turn protection is needed, the less restrictive protected/permissive phase should be used unless thee is a severe safety problem which necessitates the use of protected only phase. The permissive only phase is recommended for low left-turn and opposing volumes.