Design and field evaluation of cooperative adaptive cruise control with unconnected vehicle in the loop

To fully harvest the benefits of vehicular automation and connectivity in the mixed traffic, a cooperative longitudinal control strategy named Cooperative Adaptive Cruise Control with Unconnected vehicle in the loop (CACCu) has been proposed. When encountering an unconnected preceding vehicle, CACCu enables a Connected and Automated Vehicle (CAV) to benefit from communicating with a connected vehicle further ahead, rather than completely falling back to Adaptive Cruise Control (ACC). To validate the feasibility of CACCu, this study developed and tested a CACCu system with real vehicles in the field. A speed-command-based CACCu controller is designed and parameterized for optimizing the anticipated string stability. The experiment was conducted with two automated vehicles equipped with Mobileye sensors and Wi-Fi modules. The car-following performance of CACCu, in comparison with ACC and human driving (as the ego vehicle), was evaluated in the real-traffic scenarios constructed using NGSIM vehicle trajectory data. Over the 6 test runs for each control method, it was found that CACCu reduced 10.8% acceleration Root Mean Square (RMS), 60.8% spacing error RMS and 6.2% fuel consumption from ACC's, indicating advantages of CACCu in control accuracy, ride comfort and energy efficiency. Compared with human driving, CACCu also reduced 17.6% acceleration and 13.4% fuel consumption. More importantly, the CACCu was able to efficiently avoid the traffic disturbance amplifications that frequently happened to ACC and human driving, which means the string stability has been significantly improved by the CACCu.