Influence of non-driving related tasks on driving performance after takeover transition in conditionally automated driving

In conditionally automated driving, drivers are required to respond to takeover requests (TORs) and resume manual driving of the vehicle in situations where the conditionally automated driving systems are ineffective. Prior to TORs, the driver may be engaged in Non-Driving Related Tasks (NDRTs), and their manual driving performance after the takeover transition (post-automation) may require time to return to normal. This study investigated the influences of NDRTs on manual driving performance during the post-automation period. Seventeen volunteers participated in this driving simulator study. There were three NDRTs: writing business emails (working condition), watching videos (entertaining condition), and taking a break with eyes closed (resting condition). The duration of engagement in each NDRT before resuming manual driving was either 5 min (short interval) or 30 min (long interval). When TORs were made, drivers were given 10 s (TOR lead time) to switch from an NDRT to manual driving and then continue driving on a straight highway for 5 min. The results demonstrated that driving performance was impaired during the post-automation period. A significant detrimental effect on driving performance was observed for all three NDRT conditions and both task engagement durations. This effect was particularly evident for lane control, where drivers on average spent 4-8 s per minute outside of their lane for each of the five minutes following the TOR. These results indicate that driver engagement in other tasks, even for brief periods, can increase accident risk during the minutes following a TOR. Analysis of individual driving performance revealed a subset of 5 drivers who were strongly impaired, spending 10-25 s per minute outside of their lane throughout the post-automation period. These unsafe drivers could be accurately identified from their driving behaviour during the pre-automation (control) period. Surprisingly, participants were unaware that their degraded driving performance following the takeover. These findings extend the understanding of the disruptive effect of cognitive set-switching while driving and have important implications for the design and safety of autonomous vehicles.