ADDITIONAL LOST TIME CAUSED BY PERMITTED LEFT TURNS

Permitted left-turn phasing is commonly used to increase capacities and reduce delays at signalized intersections. But, under heavy traffic volumes, when they can only be made after the green, permitted left turns interfere with the start of subsequent phases, increasing the lost times and reducing the capacities of these phases. The primary objective of this research was to determine the additional lost time caused by permitted left turns. Additional lost times of protected left-turn phases, which were caused by cross-street permitted left turns, were measured at three signalized intersections. Multiple regression analysis of these data determined that the additional lost time depended on the number of permitted left turns made at the end of the cross-street green and the grade of the exclusive lane from which the protected left turns were made. The effects of the additional lost time on intersection capacity were evaluated. The results of this research provide a means of acounting for these effects in the analysis and design of signalized intersections.