Quantifying Take-Over Quality

Abstract

Due to recent advancements in automated driving systems, drivers are able to withdraw themselves from the control loop of the vehicle in certain driving situations. However, system limits occur relatively frequently, which results in the driver having to take back control. It is argued most currently used take-over quality quantification methods, such as identifying the minimum time-to-collision or maximum lateral acceleration, neglect inherent criticality of the driving scenario. This can lead to poor overall quality assessment, especially in challenging take-over scenarios. This thesis proposes a novel method of quantifying how well the driver performed in the task of executing an emergency automation-to-manual control takeover, by means of a scenario-specific quality reference in the form of an optimized trajectory. Firstly, a human-in-the-loop driving simulator study was carried out using a high fidelity 6-DOF driving simulator (n=25). The simulated environment consisted of a two-lane highway setting. During the drive, six different automation-to-manual takeover scenarios occurred. Optimized trajectories were also generated for these scenarios, using a State-of-the-Art trajectory planner developed at Volkswagen Group Research Facility, Wolfsburg. The independent variables were the time budget (5s, 7s, and 20s), and the traffic density (5 veh/km, and 10 veh/km). A variety of dependent variables were determined for both the human driver trajectories and the optimized trajectories: minimum time-to-collision, minimum distance-to-lane-boundary, minimum distance-to-overtaking-vehicle, maximum forced braking of the overtaking vehicle, maximum and standard deviations of accelerations (lateral and longitudinal), maximum and standard deviations of jerk (lateral and longitudinal), and lateral quickness. Based on the findings from this human-in-the-loop driving simulator study and the generated optimized trajectories, a quantification framework was developed. The framework subdivides take-over quality assessment into two separate parameters. One with regard to safety, and one with regard to comfort. The safety parameter quantifies criticality of the human driver take-over based on the sum of normalized weighted quantification scores. These scores are computed for the metrics minimum time-to-collision, minimum distance-to-lane boundary, minimum distance-to-overtaking vehicle, and maximum forced braking of the overtaking vehicle, and are based on the difference to the metric values corresponding to the optimized
trajectory. The comfort parameter quantifies comfort in a similar manner based on the metrics lateral quickness, maximum lateral and longitudinal jerk, and standard deviation of lateral and longitudinal jerk. The final quantification scores are comprised of a value between 0 and 1 for both the safety and comfort parameters. A perfect score of 0 would indicate all metrics were identical, or better than the optimized reference trajectory. A value of 1 indicates a crash for the safety parameter, and highly uncomfortable driving for the comfort parameter. The resulting quantification framework is scenario-specific as the quantification is performed relative to an optimized reference trajectory.