The Cooperative Driving Automation Phase II project implemented a hierarchical controller integrating a cloud-based speed planner with onboard driving automation controllers. Conducted as a field test on I-680N traffic in California, a fleet of connected and automated vehicles applied real-time speed advisories to preempt shockwaves and reduce stop-and-go behavior. Key performance metrics – including hard-braking events, time-to-collision (TTC) occurrences, acceleration variability and stoppage time – demonstrated significant improvements: up to an 85% reduction in intense braking, elimination of sub-2-second TTC events, 20% smoother driving speed fluctuation, and a 70% drop in near-stop time. Results validate this approach’s feasibility and safety benefits for real-traffic smoothing.

• Understanding the hierarchical CCM system combining cloud speed planner with local vehicle controllers
• Recognizing measured safety gains: up to 85% reduction in hard-braking events
• Appreciating key performance metrics: time-to-collision, acceleration distribution and stoppage time
• Learning implications for scaling CCM: macroscopic impact and recommendations for broader deployment