Developing an actuated signal control strategy to improve the operations of contraflow left-turn lane design at signalized intersections

Contraflow left-turn lane (CLL) design has been increasingly used in China to help relieve traffic congestion associated with left-turning vehicles at signalized intersections. With the CLL design, one or multiple left-turn lanes are setup in the opposing through lanes adjacent to the median. The basic idea of the CLL design is to provide additional capacity to left-turning vehicles by making use of the opposing through lanes. The primary objective of the present study was to propose an actuated signal control strategy to improve the operations of the CLL design at signalized intersections. The proposed control strategy introduced an extra stage between the presignal and the main signal at the signalized intersection with the CLL design. Two detectors were installed: one at the upstream median opening and the other at the contraflow lane. A procedure was proposed for optimizing the distance between the upstream median opening and the main signal, such that the discharge rate of the left-turning vehicles and the utilization rate of the contraflow lane can be maximized. Simulation experiments were conducted to compare the performance of the proposed actuated control strategy versus the fixed time control strategy. The results show that the proposed design concept outperforms the fixed time control strategy in increasing capacity and reducing delay for left-turning vehicles.