## 3 Takeover Experiment Results and Discussion
### Multimodality Takeover Request  
As shown in Figure 8, the multimodality takeover experiments were conducted in the same course as the single modality experiment. One of the complex notification methods was provided while driving the course twice. When a complex notification including visual, auditory, and haptic features was provided, the driver reaction to the takeover scenario was observed 377 times, and the results are shown in Figure 13. In the case of a complex modality composed of two notifications, no significant difference in any of the dependent variables with one-way ANOVA (tTOR, \(p\) = 0.065; tEyeIn, \(p\) = 0.22; tEyeMv, \(p\) = 0.98; Ap, \(p\) = 0.65; Br, \(p\) = 0.10; Steer, \(p\) = 0.29) was observed, as with the single-modality result. However, a difference in terms of the increase in the switching time, brake, and steering operation timing was observed, which are important variables in the takeover response. If all three notifications were included in the multimodal notification, the brake timing (\(p\) = 0.034) and steering timing (\(p\) = 0.006) were distinct, while the takeover time (\(p\) = 0.058) was slightly different. Regardless of the detailed notification configuration, when data were analyzed by dividing them into single, dual, and triple modalities, apparent statistical differences were observed (tTOR, tEyeIn, Br, Steer: \(p\) < 0.0001, tEyeMv: \(p\) < 0.05). The results confirmed that driver responsiveness differed depending on the complexity of the notification rather than its type. The multimodal notification method took about 2 s of takeover time, and the road fixation time was within 1.5 s. Therefore, the warning delivery effect to the driver was superior to the single modality notification (Table 3). As with the results of the single modality, the experimental results were good when a visual notification was included. However, there were many negative responses in the questionnaire, and the score was relatively low (Figure 14, average scores are 5.26, 5.31, 6.15, 6.52). In the case of auditory and haptic notifications, the overall score was similar  
Figure 11: Survey evaluations for single modality TOR (\(n=39\)). Figure 12: Short answer questionnaire evaluation results. to that when all notifications were provided, and the short-answer question about the effectiveness of the notification method in Figure 12 ranked second. Among the ten questions in the postdrive questionnaire, items with similar meanings were classified into four categories: \"efficient/helpful\", \"inefficient/uncomfortable\", \"familiar/preferred\", and \"applicable to automated vehicles\", as shown in Figure 12. Overall, as the most positively scored method for takeover notification, all three modes, sound and vibration, and sound and visual notification were selected, in that order. Many responses indicated that visual notifications were easy to miss if the participants did not keep an eye on the screen. Furthermore, there were cases wherein the sound notifications were not delivered well because of the heavy noise while driving, or they were mixed with the sound of the NDRT content. The vibrotactile seat notification, which is always in contact, was the most effective for getting the driver's attention, such that it was the most distinguished from the general driving scenario. However, there were negative evaluations of this notification method, which pointed out that it caused discomfort or anxiety (due to surprise) depending on the location or intensity of the vibration. We analyzed the correlation between personal preference and takeover performance, which has been suggested as a subject for further study. Each participant's quantitative questionnaire evaluation results were regarded as personal preferences, and the correlation with gaze response and takeover time was verified. For correlation analysis, Pearson correlation coefficients were calculated.