Dynamic Control Cycle Speed Limit Strategy for Improving Traffic Operation at Freeway Bottlenecks

In recent years, variable speed limit (VSL) has been used to decrease the total travel time and alleviate the traffic congestion on freeway. To improve traffic efficiency, we proposed a novel VSL strategy considering dynamic control cycle in this study. An extension of the cell transmission model was used to depict the traffic characteristics under VSL control, and the VSL strategy was designed to provide multiple control cycles. A probability formula was developed and used to determine the optimal quantity of control cycles in the VSL strategy. An objective optimization function was formulated with the aim of minimizing total travel time. A sensitivity analysis was applied to compare different control strategies under a variety of road bottleneck structures by both the numerical analysis and simulation experiments. The results show that dynamic control cycle VSL strategy outperformed other control scenarios and effectively reduced traffic congestion duration and enhanced the service level of freeway network.