Operational Analysis And Optimization Of The Contraflow Left-turn Lane Design At Signalized Intersections

Signalized intersection is the key component and bottleneck in the urban traffic network,where limited spatiotemporal resources are shared by conflicting traffic demand from various directions.For intersections with heavy demand,traffic signal control and optimization is the most widely used technique for improving safety and efficiency performance.However,the urbanization in China has brought an escalating traffic demand.In this condition,the conventional approaches are not sufficient to serve the increasingly congested signalized intersections.Therefore,numerous unconventional treatments have been applied to improve the operational performance of the signalized intersections with heavy demand.The contraflow left-turn lane design(CLL),as an emerging treatment to heavy left-turn demand,has drawn a lot of attention and been applied in several metropolises in China.The basic idea of the design is to provide additional capacity to left-turning vehicles by making use of the opposing lanes dynamically.However,in practice,the CLL design is designed and implemented mainly based on the empirical experience of local traffic authorities,without scientific analyze and optimization.The current practice significantly undermined the potential benefits of the CLL design,due to the lack of comprehensive understanding of the uniqueness of the design.To this end,the present dissertation aimed to present a systematic and practice-oriented analysis to the design,evaluation,and optimization of the CLL design.The present thesis is supported by the Key Program of the National Natural Science Foundation of China(Grant No.51238008).It is expected that the results will help traffic engineers and researchers improve traffic performance at signalized intersections with CLL design.The thesis will mainly focus on the following topics.(1)The unique operation and driver behaviors of the CLL designThe traffic operation of the CLL design is significantly different from conventional designs.Specifically,certain left-turning vehicles will advance into the contraflow lane under the control of the pre-signal so that their travel delay is decreased.This unique operation brings special patterns in traffic operation,and also unexpected driver behavior in practice.Therefore,the present dissertation seeks to reveal the underlying patterns and mechanisms in various aspect including signal control plan,headway,lane balance,and queue behavior.(2)Operational analysis with fixed-time control strategy at signalized intersectionsAll the currently used contraflow left-turn lane design is implemented at signalized intersections with the fixed-time control strategy.Therefore,understanding the operational performance of CLL design in such conditions is critical to both engineering practice and academic research.To this end,the present dissertation will mainly focus on the capacity,delay and queue length estimation,respectively,based on field data collected at signalized intersections with CLL design.Specifically,the dissertation developed a probability model for estimating the capacity of the CLL design and found that the capacity can only be approached asymptotically,which is distinct from conventional designs;the cumulative arrival-departure method was used for estimating the control delay of the CLL design and found that there could be residual queues even when the demand is smaller than capacity;an integrated model with shockwave and driver behavior analysis is developed for estimating the queue length of the CLL design.(3)Actuated control and optimization of the CLL design.To address the limitations of the contraflow left-turn lane with fixed-time control strategy,an actuated control framework is proposed in the present dissertation.With the proposed actuated control strategy,left-turning vehicles could use the contraflow lane optimally.In addition,the key parameters in the standard actuated control system,including the minimum and maximum green time duration are determined considering the uniqueness of the CLL design.(4)Operational analysis of the CLL design with close upstream intersectionsThe arrival distribution was generated using a platoon dispersion model.A stationary condition in which the performance of the contraflow left-turn lane design is stable in any stationary cycles was defined.It was proved that the CLL system will always converge to the stationary condition after a few cycles if the arrival distribution is fixed.Performance analysis and optimization are conducted based on the stationary condition.(5)CLL design and platoon control with connected and automated vehiclesThe present dissertation discussed the possible evolution of the contraflow left-turn lane design with connected and automated vehicles.The signal control plan optimization problem is defined and solved in such conditions.Moreover,the platoon control algorithm of both left-turning and through vehicles are developed to support the proposed design scheme.