Messages for Cooperative Adaptive Cruise Control Using V2V Communication in Real Traffic
Automated vehicle technologies have been implemented in practice progressively for at least a decade in passenger cars and commercial vehicles. A predecessor technology was cruise control (CC) that regulates the vehicle speed to the driver’s desired/selected speed regardless of traffic immediate in front, so the driver needs to adjust the set speed for a proper following distance. The first stage of automation is adaptive cruise control (ACC) that incorporates forward remote sensor detection such as radar/lidar for front target detection, tracking, and relative distance/speed estimation. ACC involves both speed and relative distance control. Although ACC advances significantly beyond CC, it still cannot maintain string stability for multiple vehicles in tandem with a short enough following distance, i.e., if three or more vehicles in tandem are in ACC mode and if the leader vehicle speed fluctuates due to traffic ahead, this fluctuation will be amplified toward the upstream which will eventually cause stability problems for the whole string. The third stage, which is still underway for research and tests, is cooperative ACC (CACC) which is basically ACC plus extra information from V2V (vehicle-to-vehicle) DSRC (dedicated short range communication). Thanks to the delay reduction achieved with V2V information, CACC is able to maintain string stability even if the overall traffic speed fluctuates. This will also significantly improve safety. Although the BSM (basic safety message) Part I [1,2] was set as a standard to support cooperative collision warnings, it is not adequate for CACC control. It is therefore necessary to come up with a minimum set of messages that satisfy the needs of CACC as well as active safety (to enhance vehicle and driver safety with automatic control technologies).