## 1 Introduction
Besides the visual input information, other types of external information received by various drivers, including auditory information and tactile information, are also required for them to make driving decisions. Based on the integration of all these types of information [17; 18], drivers will perform cognition, generate corresponding psychological feelings, and finally make the driving decisions that they think are optimal [19]. Through vehicle experiments, the study [20; 21] has shown that the main risk factor in foggy environments is visibility, which can lead to missing or even wrong visual information in drivers, namely visual illusions. However, regardless of the differences between drivers in individual culture, driving proficiency, and visual acuity, road space and climatic environments have consistent effects on humans' psychological feelings. When studying the factors influencing drivers' driving safety in the area of road traffic, scholars have focused on the influence of road alignment, driving visibility, illuminance, and adverse climate conditions (such as rain, fog, ice, and snow) on road traffic safety. However, there are few studies that explore road traffic safety from the perspectives of information content and driving information demand, and even fewer studies that analyze the influence of required driving information content and changes of the information content caused by harsh climate conditions (such as fog) on drivers' psychology and driving safety. According to investigations, most agglomerate fog road sections on China's expressways cannot be timely restricted and closed to traffic, so installing guiding lamps along the road sections where agglomerate fogs take place frequently is an effective method to reduce safety risks in low-visibility foggy sections and also a commonly used engineering measure in China. The literature [22] claims that guiding facilities for traffic safety in foggy weather should be turned on when the visibility is less than 200 m. The study [23] has pointed out that it is unable to implement real-time monitoring and very hard to perform timely control on small-scale agglomerate fogs, because the length of an agglomerate fog road section is just several kilometers, and the fog occurs often unexpectedly. The main measures taken in some expressway sections in China are to set up notice boards to warn drivers [24] and install a guiding system. The current intelligent guiding system in foggy areas mainly contains two guiding methods: (1) setting up static warning signs along road sections in foggy areas and (2) installing guiding system along the road sections [25]. The two methods have the following problems in guiding traffic in agglomerate fog environments. The first method only serves as a reminder, and in low-visibility, dense fog environments, drivers cannot clearly see the prompt messages from a distance during driving. Practically, the second method is implemented as double-color strobe edge flashers installed on both sides of expressway sections, which play a role in lighting road alignment and warning against collision to some extent. However, due to the scattering effect of fog on light, the traffic-guiding effect of only lighting road alignment still needs to be verified. For now, although there are industry standards on the spacing of guiding lamps, there is no national standard in China. In addition, guiding lamps only supplement partial visual information to a certain extent, so the impact of foggy environments on driving still exists. Therefore, after installing guiding lamps, how to achieve a new human-vehicle-road balance, namely how to determine the speed limits for a foggy environment with different visibility to achieve a theoretical safe state, still needs to be solved. Integrating bio-cybernetics with road traffic engineering to investigate visual guiding mechanisms in foggy environments is the key to implementing traffic guidance in low-visibility fog or haze environments.