The Human Factors of Transitions in Highly Automated Driving

The aim of this research was to investigate the nature of the out-of-the-loop (OoTL) phenomenon in highly automated driving (HAD), and its effect on driver behaviour before, during, and after the transition from automated to manual control. The work addressed questions relating to how automation affects drivers' (i) performance in transition situations requiring control- and tactical-level responses, (ii) their behaviour in automation compared to in manual driving, (iii-iv) their visual attention distribution before and during the transition, as well as (v) their perceptual-motor performance after resuming control. A series of experiments were developed to take drivers progressively further OoTL for short periods during HAD, by varying drivers' secondary task engagement and the amount of visual information from the system and environment available to them. Once the manipulations ended, drivers were invited to determine a need to resume control in critical and non-critical vehicle following situations. Results showed that, overall, drivers looked around more during HAD, compared to manual driving, and had poorer vehicle control in critical transition situations. Generally, the further OoTL drivers were during HAD, the more dispersed their visual attention. However, within three seconds of the manipulations ending, the differences between the conditions resolved, and in many cases, this was before drivers resumed control. Differences between the OoTL manipulations emerged once again in terms of the timing of drivers' initial response (take-over time) in critical events, where the further OoTL drivers were the longer it took them to resume control, but there was no difference in the quality of the subsequent vehicle control. Results suggest that any information presented to drivers during automation should be placed near the centre of the road and that kinematically early avoidance response may be more important for safety than short take-over times. This thesis concludes with a general conceptualisation of the relationship between a number of driver and vehicle/environment factors that influence driver performance in the transition.