## 4 The Experimental Test
### Analysis of Test Results
As shown in Figure 5, the lower the visibility, the more concentrated the field of regard would be, the less the visual information would be acquired accordingly, and the greater the time lag for the acquisition of the information about roadside emergency situations and for decision-making would be. On the contrary, the higher the visibility was, the greater the saccade amplitude and frequency of the driver would be, the shorter the time for acquiring side and front road conditions would be, and the smaller the time lag for making driving decisions would be. After guiding lamps were set up on the roadside, the saccade amplitude increased, thus increasing the amount of roadside visual information to some extent, as shown in Figure 6.  
Figure 5: Changes in drivers’ blood pressure based on visibility. A clustering analysis of the blood pressure and heart rate data obtained from the tests was performed. Through comparative analysis, it was found that the lower the visibility was, the more significant the effect of guiding lamps on both sides of foggy road sections in mitigating the drivers' vision-induced psychological tension would be, and this effect in the visibility range of (0, 50 m) was more significant than that when the visibility was greater than 200 m. However, the analysis indicates that, in the visibility range of [100 m, 500 m], the lower the visibility was, the more significant the effect of guiding lamps on both sides of foggy road sections in mitigating the drivers' vision-induced psychological tension would be, with the most significant effect observed in the visibility range of [50 m, 150 m]. When the visibility was above 500 m, the existence of guiding lamps would increase the drivers' blood pressure and heart rate, namely leading to increases in their psychological stress. The above findings can be described by Figure 7.  
As shown in Figure 7, the higher the visibility, the lower the psychological relief effect of guiding lamps on the drivers would be. When the visibility was above 500 m, guiding lamps would even increase the drivers' psychological stress. The analysis of heart rate data shows that the lower the visibility, the more significant the effect of guiding lamps on both sides of foggy road sections in mitigating the drivers' psychological stress would be, and this effect in the visibility range of (0, 200 m) was more significant than that when the visibility was greater than 300 m.  
When the visibility was close to 500 m, the influence of guiding lamps on the drivers' heart rate became smaller, and the heart rate measured on the road section with guiding lamps was higher than that on the road section without guiding lamps. It can be seen that, in good weather, the higher the visibility, the lower the psychological relief effect of guiding lamps on the drivers would be, and when the visibility was above 500 m, they would even increase the drivers' psychological load. To describe the experimental findings more vividly, the test results were plotted to be a visibility-heart rate relation graph, as shown in Figure 8. It can be seen that the effect was more significant in the dense fog environment with visibility of 50-100 m, and this finding is basically consistent with that found in blood pressure tests. Figure 6: Changes in drivers’ heart rate based on visibility. The comparisons of blood pressure and heart rate of different testers are shown in Figures 7 and 8 separately. The analysis of the test data indicates that, in the four conditions of static state, driving in a fog-free environment in the daytime, driving in a dense fog environment without guiding lamps, and driving in a dense fog environment, the driving in a dense fog environment is not a significant effect. Figure 8: Comparison of the heart rate changes of different drivers. Figure 7: Comparison of blood pressure changes between different drivers.