Development of Optimal Control Strategies for Freeway Work Zone Operations
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To improve traffic mobility and safety on highway segments plagued by work zone activities, transportation professionals in recent years have focused on exploring the potentials of using various merge and speed control strategies to regulate traffic flows. This study is focused on developing an advanced dynamic merge and variable speed limit controls for work zone applications, including an integration of both controls for best use of their strengths in maximizing throughputs and minimizing speed variance in traffic flows. With respect to the merge control, this study has developed an advanced dynamic late merge (DLM) control model and its operation algorithm, based on the optimized control thresholds that take into account the interactions between the speed, flow, and available work zone capacity. The proposed DLM control allows potential users to select the control variables and to determine their optimal thresholds in response to traffic flow dynamics. On regulating the approaching vehicle speeds, this study has developed a dynamic variable speed limit (VSL) control model and its operation algorithm. The proposed VSL system has adopted the maximization of work-zone throughput as its control objective with some embedded safety related constraints with such a system, one can optimize the sequence of transition speeds for approaching vehicles in the work zone, and dynamically adjusted the set of displayed speeds so as to effectively respond to potential demand variation. To best operate the DLM and VSL controls under various congested work zone conditions, this study has also explored the potential of integrating those two control strategies in work-zone operations. The logic of an integrated control is to facilitate the merging maneuvers and minimize potential collisions with the VSL during the DLM operation period, and to coordinate the sequence of VSM messages generated from both control algorithms. The numerical experiments have demonstrated that the integrated control can take full advantage of the strengths from both DLM and VSL controls, and offer the operational environment that is likely to yield a higher traffic throughput and lower speed variance than those operated independently.