Evaluating Mental State of Drivers in Automated Driving Using Heart Rate Variability towards Feasible Request-to-Intervene.

As Intelligent Transport Systems (ITS) advances, more and more people will have the opportunities to drive vehicles with autonomous capabilities. This rise in number of semi-autonomous vehicles also gives rise to several challenges with regards on how human factors come into play in interacting with the vehicle's Automated Driving System (ADS). One important interaction of an ADS with Level 3 Conditional Automated Driving capabilities is Request-to-Intervene (RTI), which alerts drivers to takeover the vehicle during an automated driving session, however, the driver is not necessarily ready to receive the authority. To see whether an ADS can detect the readiness of the user for RTI, in this preliminary study we evaluated the mental states of ADS users in naturalistic driving conditions by comparing them with those of drivers and passengers. The mental states were evaluated by measuring their heart rate and by calculating specific features of Heart Rate Variability (HRV), specifically NN50 and pNN50 indices, during driving events (turning, lane changing, and stopping) and no-events. The results showed the NN50 and pNN50 values of manual driving were significantly different from those of ADS driving and passenger, suggesting that ADS driving has a higher level of relaxed state. In addition, events such as lane-changing in the ADS driving did not induce significantly different NN50 and pNN50 from nonevent situation, which may imply the participants did not pay attention to such events.