Many congested intersections have heavy traffic volumes on movements where there is insufficient capacity due to geometric limitations. Installing pre-signals at midblock locations and reorganizing traffic upstream approach of an intersection is a promising and cost-effective method to address these capacity limitations. This paper focuses on developing and evaluating a coordinated optimization model for an isolated intersection approach with pre-signals to increase protected left turn phase capacity. The pre-signal model is based on two principles: (1) Explicitly capturing the interaction between the pre-signal signal and the main-signal by modeling the queuing process and capacity constraints of temporal and spatial limitations of the intersection; and (2) Optimizing the signal timings of both the pre-signal and the main-signal as well as the offset between them to produce the best operational strategy for the approach. The minimum green time required and the delay minimization problems are considered. Extensive experimental analysis has shown that the pre-signal model outperforms the conventional control method (without pre-signal). Sensitivity analysis of the signal timing method was also conducted to assist traffic engineers with selecting the appropriate length of the sorting area, phase sequence and early starting time of pre-signals. The results from this study offer a basis for traffic practitioners, researchers, and authorities to design and utilize pre-signals in situations where there is a need to increase intersection capacity for congested movements.
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