## 4 Experimental Design and Results
### Ablation Experiment  
To comprehensively assess the performance of the multimodal data-fusion system under different driving speeds, this study conducted ablation experiments under four driving conditions: high-speed driving, fast driving, low-speed driving, and traffic congestion. By sequentially removing a specific modality signal (such as the heart rate, respiratory rate, skin conductance, or body pressure distribution), the study analyzed the impact of different signals on driver-state monitoring in various traffic conditions, thus verifying the contribution of each modality signal and the robustness of the system. In each driving condition, the system collected data on the driver's heart rate, respiratory rate, skin conductance, body pressure distribution, and vehicle status. Accordingto the experimental design, individual modality signals were removed in sequence while keeping other signals intact to analyze the effect of a single signal on the overall monitoring performance. For each speed condition, the following five sets of ablation experiments were conducted:  
Complete multimodal fusion: This includes heart rate, respiratory rate, skin conductance, and body pressure distribution signals. Removal of respiratory rate signal: Retaining heart rate, skin conductance, and body pressure distribution signals. Removal of body pressure distribution signal: Retaining heart rate, respiratory rate, and skin conductance signals. Each group of experiments was conducted under the same driving conditions, ensuring consistent driving times, road conditions, driver emotions, and fatigue states to guarantee the reliability of the comparative results. The evaluation metrics for each group of experiments were the monitoring precision, accuracy, recall, F1 score, and false positive rate. Tables 5-8 presents the experimental results of the monitoring performance after removing  
Heart rate signals are one of the most critical physiological indicators in all driving scenarios, whether during high-speed driving, rapid driving, low-speed driving, or traffic congestion. The fluctuations in heart rate are closely correlated with the driver's fatigue and stress levels. During high-speed driving, drivers need to maintain a high level of concentration, and changes in heart rate often serve as important indicators of driver fatigue. Experimental results show that after removing the heart rate signal, the system's accuracy decreased by 9.76%, indicating that heart rate signals play a decisive role in detecting fatigue and stress levels. In rapid driving scenarios, heart rate signals continue to contribute significantly to system performance, especially when drivers face sudden situations or increased pressure, which leads to rapid heart rate increases. The system's accuracy dropped by 9.46% after removing the heart rate signal, further validating its key role in monitoring the physiological status. Although driving pressure is relatively lower in low-speed driving, heart rate signals still significantly contribute to fatigue monitoring. The accuracy of the system decreased by 11.59% after removing the heart rate signal, suggesting that even in low-speed driving conditions, heart rate signals can effectively reflect the driver's fatigue level. In traffic congestion, frequent braking and acceleration increase the driver's stress, and heart rate signals become particularly important in this context. After removing the heart rate signal, the system's accuracy decreased by 11.05%, indicating that heart rate signals can effectively monitor the driver's stress and tension responses during congestion. Overall, heart rate signals consistently emerge as the most important physiological signal across all driving scenarios. Their fluctuations are directly related to the driver's fatigue and stress levels, providing the most direct feedback on physiological status to the system. Respiratory rate signals play an important auxiliary role in the system, particularly in monitoring the driver's fatigue and stress levels.