The evaluation of luminance in a road tunnel based on CIE88-2004 standard to reduce road accidents

Traffic safety is a major concern all around the world. About 1.5 million people die each year from road accidents and 50 million are injured. These figures account for about 1/2 percent of all deaths in the world, making road crashes the ninth most common cause of deaths. In Iran, the number of road accidents and their fatalities is significantly higher than the world standard. As the annual incidence rate of 32 cases per 100,000 is the second leading cause of death and the most common cause of injuries. The need for road tunnels increased with the development of road transport to reduce traffic congestion, reduce travel time and save energy. The construction of these tunnels created visual problems associated with the physiological mismatch of the driverschr('39') eyes at the inlet and outlet of the tunnel resulting in an increased risk of traffic accidents. Therefore, standards were developed to improve safety and reduce traffic accidents in these tunnels, including CIE 88-2004, PR-22-05 and IESNA. In order to safely cross the road tunnel, it is essential that all drivers have sufficient information about the road ahead, potential obstacles, and the presence and performance of other drivers. Therefore, one of the key factors in preventing accidents in road tunnels is the installation of lighting systems. The purpose of lighting in road tunnels is to provide an appropriate degree of safety for drivers during entry, transit and exit of the road tunnel, both over the day and night. According to CIE 88-2004, the purpose of road tunnel lighting is to create a safe and comfortable environment throughout the tunnels so that drivers along the road will have sufficient information on the road, possible obstacles and the direction of movement of other vehicles. According to the CIE Technical Report, drivers have different visual problems as they approach, enter, and exit the tunnel. One of the main causes of road accidents in tunnels is the lack of design of an optimal lighting system. Therefore, the aim of this study is to evaluate the luminance in a road tunnel based on CIE88-2004 standard in order to reduce the number of accidents caused by visual problems. 

In the present study, CIE88-2004 was used to evaluate the luminance in road tunnels. Early stages in assessing and evaluating luminance road tunnels include the determination of safety stop distance, equivalent veiling luminance, atmospheric luminance and wind screen luminance. The safety stop distance is equal to the sum of the distance between the barrier processing in the brain and the driverchr('39')s motor response to the brake, so that this distance prevents the vehicle from colliding with potential obstacles in road tunnels. Equivalent veiling luminance is caused by the reflection of light from the environment around the tunnel, to the driverschr('39') eyes, resulting in reduced contrast in the tunnels. Luminosity caused by factors such as dust in the atmosphere that make light scattering is called atmospheric luminance. One of the main reasons for the reduction of contrast in the eyes of drivers is due to the diffusion of light in the windshield. To determine the equivalent veiling luminance, photographic camera with 35mm lens and Holiday-Stiles was used. In order to determine the brightness of the equivalent view, the percentage of environmental factors (sky, road, rock, building and grassland) were determined by drawing a polarized halide diagram on the tunnel entrance photo and considering the networking of each segment of the rings. It should be noted that in some areas, the luminance level was not included in the luminance calculations due to the dashboard and the roof of the car, which prevents drivers from glaring. To determine the atmospheric luminance and wind screen luminance, HAGNER luminance meter model S3 was used. After determining the equivalent veiling luminance, atmospheric luminance and wind screen luminance of the vehicle, the required luminance in different areas of the study tunnel was designed using the CIE88-2004 standard. According to CIE-88-2004, in order to prevent road accidents caused by poor lighting, road tunnels are divided into 5 areas: access zone, threshold zone, transition zone, interior zone and exterior zone. The access zone is the distance before entering the tunnel which is equal to the length of the safety stop distance. The threshold zone is the first area inside the tunnel that requires a great deal of artificial lighting to manage and control the adverse effects of the black hole phenomenon. In the transition zone, due to the driverchr('39')s transition from the bright environment outside the tunnel to the dark environment inside the tunnel, the eye must adapt to these changes in brightness. The interior zone is the longest area in the tunnel and usually requires low illuminance levels. Exterior zone; this area again prepares the eyes for sunlight and usually requires a high level of illuminance to adapt the eye from the tunnel to the light outside the tunnel.

In determining the safety stop distance, the average reaction time was set to 1 second according to the CIE standard recommendation. Based on the tunnel location and the 10-year data of Ilam Weather Station No. 40780, the average annual rainfall was 73.8 days. According to the Paris recommendation, the coefficient of friction between the road and the tire in places where the average annual rainfall is more than 75 hours, the road condition is considered wet in access zone of tunnel. Therefore, the coefficient of friction between the road and the tire was 0.35, taking into account the wet road surface and the maximum speed allowed by vehicles passing through the tunnel. Then the safety stop distance in the tunnel was set 69.6 m. After estimating luminance in all polarized halide diagram rings, the equivalent veiling luminance was determined equal to 127.5 candela per m2. Also, the wind screen luminance and atmospheric luminance were measured 234.4 and 308 candela per m2, respectively. Then, according to these measurements, the required luminance levels in the first and the end of the second part of the threshold zone were determined as 576 and 230.6 candela/m2, respectively. Then, according to the safety stop distance (69.6 m) and heavy traffic volume, the required luminance level of the interior zone was 6.2 candela/m2. After determining the luminance in the interior zone of the tunnel, the type of tunnel (long, very long) must be specified. Therefore by reducing the length of the threshold zone (69.6 m), transition zone (432 m) and exterior zone (89.6 m) of the entire tunnel length (1200 m), the length of interior zone (608.8 m) was determined. Thus, by dividing the maximum permissible speed of vehicles inside the tunnel by the length of the interior zone, the time interval by the interior zone was determined to be 33.8 seconds. Because the time interval in the interior zone for studied tunnel was more than 30 seconds, the tunnel was classified as very long tunnel and the luminance in the second part of the interior zone was 2.3 Candela/m2. Also, according to the CIE standard, the luminance at the end of the exterior zone increased by 5 times compared to the second part of the interior zone, which equals 11.5 candela per square meter.

Lighting in road tunnels is of particular importance as neglecting it can cause major problems with driver safety such as black hole phenomena (before entering the tunnel), mismatch (during tunnel entry) and white hole phenomena (as exiting the tunnel). In this study, the required luminance (designed) in the initial part of the threshold zone was 576 candela per square meter with respect to the equivalent veiling luminance resulted from the tunnel surrounding, wind screen luminance and atmospheric luminance. This amount of luminosity required at the tunnel entrance can be reduced in appropriate ways such as; installation of asymmetric lighting systems inside the tunnel (of course, asymmetric lighting systems have some disadvantages, such as the high need for the high ceiling, also, not adjusting asymmetric lighting systems in the opposite direction of traffic can increase the flicker effect). Another way to reduce the required luminance is to reduce the luminance of the surrounding of tunnel environment. By changing the surfaces around the tunnel from high reflective materials to low reflective materials (planting grass and trees), the level of luminance can be significantly reduced in the eyes of drivers in the tunnel access zone. In road tunnels, drivers should identify road barriers at least at safety stop distance to prevent accidents. Effective ways to quickly adapt the driverschr('39') eyes to the dark inside the tunnel have been investigated, including the installation of semi-transparent structures to move the threshold zone to the outside of the tunnel. This allows the use of sunlight to achieve the desired luminance. Although most problems occur at tunnel entrances, the eye matching from low luminance inside the tunnel to high luminance outside the tunnel in the exterior zone of tunnel should not be ignored. Although this process is relatively fast, however, a high difference in luminance between the end of the tunnel and the environment outside the tunnels should be avoided.