Hybrid Intersection with Pre-signal: An Innovative Approach to Increase Intersection Capacity

Exclusive left-turn phases are often adopted to ensure the safety and efficiency of left-turn movements in conventional intersection signal timing schedules. Due to the need for at least two exclusive left-turn green phases for four-way intersections, some approach lanes for left vehicles are spare during the green phase, resulting in intersection capacity drop. To fix this drawback, we propose a hybrid intersection strategy based on pre-signal and sorting areas in this study. The ad hoc traffic flow control method of the hybrid intersection reduces the number of exclusive left-turn phases from at least two, in conventional four-way intersection conditions, to only one. Furthermore, sorting areas charge pre-organized vehicles during green pre-signals and discharge vehicles during green intersection signals, so that the hybrid intersection can be used for as many approach lanes as possible to discharge vehicles during the green intersection signals. Considering traffic demand, lane allocation, and signal schedule, we construct binary mixed-integer linear programming (BMILP) to formulate the capacity maximization problem of the hybrid intersections. A series of case studies show that, the hybrid intersection strategy can achieve higher capacity significantly than other pre-signal strategies and conventional roundabout. In addition, the hybrid intersection strategy can achieve optimal capacity when demand of left-turn vehicles (LVs) and through vehicles (TVs) are huge and relatively close, and when the cycle length is moderate (around 70s).