A cooperative control method for connected and automated vehicles in ramp merging areas: Incorporating speed control and lane changing

Ramp merging areas frequently constitute bottleneck sections prone to traffic congestion and safety incidents. The emergence of Intelligent Connected and Automated Vehicle (CAV) technology offers a novel paradigm for addressing ramp merging control challenges. This study proposes a cooperative hybrid control strategy named SCLC (Speed Control and Lane Changing) for this scenario. Adopting a hierarchical control architecture, the strategy consists of two core components. The speed control strategy regulates car following behaviours within the same lane and dynamically adjusts merging speeds for both mainline and ramp vehicles. Simultaneously, the lane changing strategy, governed by a utility selection function, guides vehicles on the mainline outer lane to merge into the inner lane, thereby releasing space for merging traffic. Comprehensive evaluations of the proposed strategy were conducted via microscopic and macroscopic simulations, focusing on traffic efficiency, safety and comfort metrics. Results indicate that the SCLC strategy significantly enhances traffic performance in the merging zone, effectively eliminating merging conflicts and smoothing traffic flow. Specifically, microscopic simulations confirm that the strategy yields substantial improvements in mitigating delay, traffic emissions, and ride discomfort, while eliminating potential collision risks. These benefits are further corroborated by macroscopic evaluations, which demonstrate reductions in delay and emissions by approximately 64% and 60%, respectively, alongside decreases in collision risks and passenger discomfort by over 98% and 90%. Moreover, the SCLC strategy maintains robustness across varying traffic flow rates and ramp vehicle ratios, with performance improving with the extension of the communication zone length.