Developing a Dynamic Speed Control System for Mixed Traffic Flow to Reduce Collision Risks Near Freeway Bottlenecks

Connected and automated vehicles (CAVs) have the advantages of improving road safety and traffic efficiency. This study proposes a dynamic speed control system for a two-lane scenario to reduce collision risks near freeway bottlenecks for mixed traffic flow, consisting of both CAVs and human driven vehicles (HDVs). The control system includes two major strategies, the dynamic deceleration strategy and uniform lane-changing strategy. The core idea of dynamic deceleration is to command the CAVs to slow down proactively and form moving barriers to guide the following HDVs to slow down before the bottleneck. The establishment of uniform lane-changing strategy aims to improve the uniform coefficient of CAVs for each lane in the mixed traffic flow, and three different solving methods are applied for uniform lane-changing strategy to further improve safety. Simulation experiments are designed, and the performance of the system is investigated in terms of its safety and efficiency. Sensitivity analysis has been carried out on the length of the area where uniform lane-changing strategy is implemented. The results indicate that: (1) dynamic deceleration strategy based on CAVs can effectively reduce collision risks; and (2) the uniform lane-changing strategy can further improve the performance of the dynamic deceleration strategy.