Effect of Post Take Over Situation Complexity on Take Over Behaviour and Driver's Trust in Conditionally Automated Driving

Abstract

In conditionally automated driving, drivers should be free to engage in non-driving-related tasks until warned by the system to take over. Over-reliance on automation can lead to dangerous driving behaviour such as engagement in non-related driving tasks during the transition phase and delayed response to take over requests. Take-over time and quality were shown to be influenced by several factors such as involvement in a secondary task, the complexity, and criticality of the driving situation, or the modality and intensity of the take-over request. We found a paucity in research into the effect of post-take-over complexities. Understanding the effect of traffic situation just after transition phase on driver's take-over behavior is crucial for developing highly automated driving systems regarding safety. Therefore, we conducted a driving simulator experiment and tested the influence of post take-over situation complexity on take-over behaviour and driver's trust during automation initiated take-overs. Twenty-four participants drove two conditions, one with high situation complexity and the other one with low situation complexity in a fixed-based driving simulator. Participants were driven with conditionally automated driving and asked to play a game until warned by the automation to take over. The take-over performance was assessed based on safety performance (take over reaction time and no. of collisions) and subjective measures (self-reported perceived trust and technology acceptance). Sub response times in terms of the first gaze and hands on the steering wheel time after the first TOR is prompted, were also analyzed using video annotations. Results showed that situation complexity does not affect take over reaction time, though it significantly affects trust in automation rating. No significant relationship has been found between sub response time and overall take-over reaction time in both situation complexity. Eleven collisions occurred, which indicates that some participants fail to resume control on time. Some participants did not resume control at all and trusted on the automation in both complexities. Higher trust rating in low complexity situation indicates that drivers might develop complacency, resulting in degraded take over ability in unexpected take-overs and delayed response to take-over. This suggests that people develop a wait-and-see attitude and only reclaim control when they feel the need for it. These findings can help design automated technology and policies to ensure the inherent risk in conditionally driving automation can be eliminated.