S.F. Varotto

Empirical Longitudinal Driving Behavior in Authority Transitions Between Adaptive Cruise Control and Manual Driving

Automated vehicles are expected to have a substantial impact on traffic flow efficiency, safety levels, and levels of emissions. However, field operational tests suggest that drivers may prefer to disengage adaptive cruise control (ACC) and resume manual control in dense traffic conditions and for maneuvers such as changing lanes. These so-called authority transitions can have substantial effects on traffic flow. To gain insight into these effects, a better understanding is needed of the relationships between these transitions, longitudinal dynamics of vehicles, and behavioral adaptations of drivers. In this context, a driving simulator experiment was set up to gain insight into the effects of authority transitions between ACC and manual driving on longitudinal dynamics of vehicles. Participants were assigned randomly to one of three conditions. In the control condition, participants drove manually. In the first experimental condition, a sensor failure was simulated at a specific location where drivers were expected to resume manual control. In the second experimental condition, drivers switched ACC off and on by pressing a button whenever they desired. Statistical tests indicated that the distributions of speed, acceleration, and time headway differed significantly between the three conditions. In the first experimental condition, the speed dropped after the sensor failure, and the time headway increased after the discretionary reactivation of ACC. These results seem to be consistent with previous findings and suggest that authority transitions between ACC and manual driving may significantly influence the longitudinal dynamics of vehicles and potentially mitigate the expected benefits of ACC on traffic flow efficiency.

Resuming manual control or not?: Modelling choices of control transitions in full-range adaptive cruise control

Automated vehicles and driving assistance systems such as adaptive cruise control (ACC) are expected to reduce traffic congestion, accidents, and levels of emissions. Field operational tests have found that drivers may prefer to deactivate ACC in dense traffic flow conditions and before changing lanes. Despite the potential effects of these control transitions on traffic flow efficiency and safety, most mathematical models evaluating the impact of ACC do not adequately represent that process. This research aimed to identify the main factors influencing drivers’ choice to resume manual control. A mixed logit model that predicted the choice to deactivate the system or overrule it by pressing the gas pedal was estimated. The data set was collected in an on-road experiment in which 23 participants drove a research vehicle equipped with full-range ACC on a 35.5-km freeway in Munich, Germany, during peak hours. The results reveal that drivers were more likely to deactivate the ACC and resume manual control when approaching a slower leader, when expecting vehicles cutting in, when driving above the ACC target speed, and before exiting the freeway. Drivers were more likely to overrule the ACC system by pressing the gas pedal a few seconds after the system had been activated and when the vehicle decelerated. Everything else being equal, some drivers had higher probabilities to resume manual control. This study concludes that a novel conceptual framework linking ACC system settings, driver behavior characteristics, driver characteristics, and environmental factors is needed to model driver behavior in control transitions between ACC and manual driving.