## 3 Takeover Experiment Results and Discussion
### Takeover Strategy  
Experimental results on the DVI configuration method, accident rate by scenario type, and effectiveness of DMS in the takeover process are summarized as follows.  
* The effect of takeover request notification type is clearly distinguished for single/dual/triple modalities (in Section 3.2, tTOR, tEyeIn, Bp, Steer: \(p<0.0001\), tEyeMv: \(p<0.05\) with ANOVA for single/dual/triple modality analysis).
* Notification modalities preferred by drivers are better at inducing driver concentration (in Section 3.2, driver preference and gaze road fixation time, 31% for r \(>0.7\), and 61.5% for r \(>0.3\) with Pearson's r).
* Depending on the type of system failure cause, the timing of the transition to emergency behavior (MRM, EM) must be different (in Section 3.3, cases with high driver recognition difficulty).
* The safety of the transition process is improved if the DMS causes the driver to check the driving scenario periodically (in Section 3.4, improvement of reaction time and takeover failure with DMS).  
Figure 17: Heart rate, respiration rate, and NDRT concentration data.  
Figure 18: Heart rate and respiration rate in manual/autonomous driving (\(n_{heart}=46\), \(n_{resplation}=79\)).  
A flow chart of the takeover process of a highly automated vehicle is provided in Figure 19 based on the results of all the experiments. At the beginning of the procedure, the system, which receives the driver's willingness to use through DVI, determines whether to wear a seat belt, and satisfies the system operational design domain (ODD). Then, it decides to switch to the autonomous driving mode. While the autonomous mode is active, the system continuously checks the driver availability with gaze and head orientation information and system operating conditions. The system periodically makes the driver aware of the driving environment to improve the reaction speed and success rate in takeover scenarios.  
When an autonomous driving system detects a failure because of various causes, the following two responses are possible:  
First, if there is sufficient time for the takeover request, visual-auditory-haptic notifications are additionally provided based on TTD (e.g., visual \(\rightarrow\) visual and auditory \(\rightarrow\) visual, auditory, and haptic). Furthermore, the warning effect can be enhanced based on driver preference within a certain range for the notification intensity and the order of addition. If the driver cannot respond within the time or the situation worsens, severe system failure occurs, and the MRM must be initiated immediately.  
Second, the EM should be carried out in scenarios where it is difficult for the driver to determine the cause or in imminent collision risk. The EM should not be terminated unless the imminent collision risk disappears or until the driver deactivates the system. The proposed strategy can improve the safety of the takeover process and improve the process of switching control rights, which could be the most dangerous moment in an autonomous driving system of Level 3 or higher. Furthermore, improving the willingness to use an autonomous vehicle is possible by providing a sense of psychological stability to the user.