Mitigating Merge Congestion with CCAM Services: A Comparative Study on A56 Italian Motorway

Traffic congestion at motorway on-ramps is a persistent bottleneck in urban networks. This study investigates a Cooperative, Connected, and Automated Mobility (CCAM) strategy for mitigating such merge congestion, focusing on a representative cooperative merging service known as Gap-Opening. In a case study on the A56 - Tangenziale di Napoli - in Italy, we employ a high-fidelity co-simulation platform (Eclipse MOSAIC) to evaluate four scenarios: a no-intervention baseline, a conventional temporary lane-closure control, and CCAM deployments with 40% and 50% connected and automated vehicle (CAV) penetration. The Gap-Opening service enables mainline CAVs to proactively create gaps for merging vehicles based on realtime Vehicle-to-Everything (V2X) communication from on-ramp vehicles. Simulation results show that the cooperative strategy significantly outperforms the traditional approach, yielding shorter average travel times and more stable traffic flow. These findings demonstrate that integrating CCAM merging services can be a more effective alternative to reactive measures, supporting smoother merging operations and improved traffic performance in congested motorway scenarios.