## 1 Background
The results indicated that the installation of decorative lights in the tunnel section reduced the fatigue of drivers and, thus, improved traffic safety. [PERSON] [19] studied the influence of lights at tunnel entrance and exit on traffic safety, and suggested that the layout design of lights at the tunnel entrance and exit should be taken into consideration. [PERSON] [20] and [PERSON] [21] investigated the movement of the eyes of drivers and found that the driver's tension would be increased when the brightness changed sharply or unevenly, which would easily cause operational errors and decrease the traffic safety. [PERSON] [22] focused on the effect of brightness on drivers' attention, and indicated that a brighter wall is more important for safety and comfort than high level of lighting, as long as the illumination is sufficiently bright. In addition, driving and staring behaviors were significantly affected by driver status, and distracted drivers are less likely to drive safely. The landscape of the tunnel will also affect the driver's concentration and reduce fatigue. [PERSON] [23] carried out a driving simulator based virtual reality driving experiment. In the 11.055 km long tunnel, drivers' reactions and brain waves were examined to correspond to two scenarios, with and without landscape images respectively. The results show that after the landscape image was installed, the driving speed and distance away from the lane centerline were affected, and both the sleepy-related brain waves and fatigue of drivers were reduced. In addition, the active safety measures based on optical illusion were studied by many scholars. [PERSON] [24] and [PERSON] [25] used the 3 ds Max software to simulate the deceleration effect of tunnel optical illusion markers, the results show that, with the combination application of high-frequency visual information and low-frequency visual information, the vehicle speed can be reduced, resulting in the improvement of the traffic safety. At the same time, [PERSON] [26] proposed a rhythm-based marking system, and the results show that the rhythmic marking in the tunnel can effectively improve driver's speed judgment accuracy and reduce driver's reaction time, and the effect of multi-color marking is better than that of single-color marking. [PERSON] [27] used questionnaires to test common delineators and a new type of flashing light separately, the questionnaire results show that these two facilities can significantly improve the tunnel traffic safety. From the previous research of our team [28], it can be found that, after the installation of a horizontal marker with reverse perspective information, the time distance of the vehicle following the vehicle is increased. What is more, the greater the dispersion of inverse linear perspective information, the greater the growth range of headway. Therefore, the visual interference to drivers can reduce the speed and improve the tunnel traffic safety [29; 30]. However, most of the current studies were carried out with simulation tests in a computer or just in the Lab, which is somewhat different from the actual traffic environment. In this research, firstly, under the common road and traffic conditions, two visual active deceleration devices were set up in a real tunnel (Yunmengshan I tunnel in China), namely (i) reverse-perspective-illusion deceleration lines (RPIDLs) and (ii) a visual-intervention deceleration device (VIDD), were used together to control vehicle speeds and reduce their dispersion. RPIDLs were used at the entrance of a long downhill tunnel, and the VIDD was used in its middle. Each device was designed with different parameter settings, such as its total length (30, 60, or 120 m), angle (15\({}^{\circ}\), 40\({}^{\circ}\), or 55\({}^{\circ}\); 60\({}^{\circ}\), 90\({}^{\circ}\), or 120\({}^{\circ}\)), color (white or yellow), and shape (straight or broken line). Then, laser velocimeters (LVs) were used to measure the vehicle speeds in the tunnel both with and without RPIDLs and a VIDD.