A road tunnel can be divided into the following major areas: the approach section, the entrance section, the transition section, the tunnel section, and the exit section.
1, close to the paragraph
The approaching section refers to a section of the road outside the tunnel, where the driver must be able to see the objects in the tunnel. This is also the stage of the driver's visual adjustment, which determines the brightness requirements of the tunnel entrance and the tunnel entrance section. During the day, due to the strong contrast between the high environment outside the entrance and the low brightness in the tunnel, and because of the visual impact of the driver's eyes on the bright environment, a black hole will be seen in the long tunnel opening and will be seen in the short tunnel opening. It is impossible to see any details in the hole in a black frame. This is called the "hysteresis of adaptation", which is the result of the fact that the human eye cannot adapt quickly.
2, the entrance section
The entrance section is the first section of the four sections in the tunnel. The driver driving near the section must be able to see the road surface at the entrance before the tunnel enters the tunnel, eliminating the "black hole" phenomenon.
The length of the inlet section depends on the maximum speed of the tunnel design, at least equal to the safe braking distance at the highest speed. This is because the farthest road surface in this section should be the background for the driver who is ready to enter the tunnel outside the safe braking distance to see the obstacle.
3. Transition section
After a relatively high threshold level of illumination, the illumination in the tunnel can be gradually reduced to a very low level, and this gradually decreasing area is the transition section.
The length of the transition section depends on the difference between the design maximum speed and the illumination level of the tail section of the inlet section and the interior section. The transition section may be divided into 1 to 3 segments according to different lighting levels.
4, the internal section
The inner section is the area within the tunnel that is far from the external natural light, and the driver's vision is only affected by the illumination inside the tunnel. The internal section is characterized by a uniform illumination level throughout the section. Since there is no need to change, the segment only needs to provide a suitable level of brightness, which is determined by traffic flow and vehicle speed.
However, this section is different from the general road and is always more dangerous than driving on a generally open road. The waste of vehicle emissions in the tunnel could not be dissipated in time, forming a white smoke in front, which was diffused into a light curtain by the light, reducing visibility. Therefore, the lighting level is required to be higher than the average road. At this low level, it is not possible to use a continuous strip of light, so interference strobe must be prevented in use.
5. Export section
In this area, the visual adaptation is from low brightness to high brightness. When approaching the tunnel exit, there is always natural light coming in. The external brightness is extremely high, which is easy to cause strong glare effect. On the contrary at night, the tunnel exit becomes Black holes, so it is difficult to see the routes and obstacles, these are issues that must be considered.
The next plan will bring tunnel lighting source requirements and lighting options.
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