Twenty participants completed test rides in a normal and an Automated Highway System (AHS) vehicle in a driving simulator. Three AHS conditions were tested: driving in a platoon of cars at 1 sec and at 0.25 sec time headway and driving as a platoon leader. Of particular interest was overreliance on the automated system, which was tested in an emergency condition where the automated system failed to function properly and the driver actively had to take over speed control to avoid an uncomfortable short headway of 0.1 m. In all conditions driver behavior and heart rate were registered, and ratings of activation, workload, safety, risk, and acceptance of the AHS were collected after the test rides. Results show lower physiological and subjectively experienced levels of activation and mental effort in conditions of automated driving. In the emergency situation, only half of the participants took over control, which supports the idea that AHS, as any automation, is susceptible to complacency. This condition received the highest risk ratings, followed by automated driving at 0.25 sec time headway. When driving automatically, most drivers preferred the longer time headway of 1 sec to vehicles in front, which may counteract the intended advantage of increased road capacity of AHS. Drivers considered "loss of control over driving" a negative aspect of AHS. It is concluded that if drivers are to reclaim control in case of system failure, and if system failure is to be expected, then the driver should not have a passive role in the system. Also, the status of automation should be clear, and system failure should be salient. (Author/publisher)
Samenvatting