Driving in long tunnels with dim illumination and dark walls offer little to none visual stimulation. The repetitive and constant distance between light sources, which provide a blink of light per second in normal driving speed, contributes to the feeling of monotony. When a situation arises that requires a quick reaction the driver will need more reaction time than normal. International studies show that accidents caused by falling asleep behind the wheel are far greater in long tunnels. The structure of a tunnel also contributes to the monotony as there are few focal points. Diversity in visual stimulation is greatly reduced compared to the outside environment, and there is a lack of variation. This provokes a negative adaptation for the senses with a reduced awareness for the environment. This causes the drivers to adapt to the monotony and reduces their ability to react in appropriate manner. So, what to do to improve driving conditions? 30/07.
Statistics show that there are less accidents in road and highway tunnels than in open space roads. However, it does seem that danger is higher in tunnels because it depends on human error, like for any other accident on an open road, but also on the spilling of dangerous materials and the subsequent combustion process that may lead to a serious fire difficult to control. Besides, trucks carrying hazardous materials are not allowed to use some tunnels. Danger in tunnels is a concentration of human, technological and environmental factors while these factors are more diluted on open roads.
Many people dislike driving through tunnels, especially long tunnels. Road users may feel insecure or anxious because of the inability to turn around, darkness, poor air quality, feeling of claustrophobia, etc. Subsea tunnels add even more handicaps and give some road users unpleasant perception, like the sentiment of being trapped or water leakage and flooding risks, to the point that they refuse to drive through them and prefer another route, even if it is a long way around. Others will drive through the tunnels, despite their fear, because an alternative route or transport means is too time-consuming or too expensive or because they can cope with their anxiety.
Long tunnels can be designed with slight curves to reduce the feeling of monotony. Also, slight curves close to the exit will reduce the risk of getting blinded by the outside sunshine.
White walls or road surfacing can make the tunnel brighter. But brightness all over (walls, roadway and ceiling) does not give good visual guidance and comfort. There should be good contrast between the colour of the walls and the road surface.
Research conducted by SINTEF has found that long tunnels and subsea tunnels have a considerable negative effect on the road users’ feeling of security. Studies from Denmark, Sweden and Austria show that anxiety for long and subsea tunnels is not only a Norwegian problem. Road users usually find tunnels too dark. Long tunnels or a chain of numerous tunnels can be monotonous and have a sleeping effect. The highway from Nice, France to northern Tuscany, Italy totals nearly 190 tunnels! Almost all of them are situated on the Ligurian coast highway in northwest Italy. The highway is a long string of viaducts and tunnels, making the journey an experience that requires uninterrupted watchfulness and self-control.
Lighting
Interior lights must be designed so that drivers' eyes can easily adjust when going in and out of the tunnel. At the entrance, when the human eye has to get used to the difference of contrast between daylight and darkness, the so-called black hole, drivers do not perceive what happens inside the tunnel until they penetrate into it and the pupil adapts to the new conditions. The same phenomenon occurs at the exit of the tunnel. Therefore, the lights at the entry and exit ramps or thresholds must be reinforced to avoid traumatic adjustment of the eye. The threshold and transition zone, directly after and before the tunnel portal, will have a length of approx. 70 metres. The purpose of this zone is to adapt the human eyes to the different light levels outside and inside the tunnel.
The central zone is the main part of the tunnel, thus the driver will experience stable light levels in this part of long tunnels. Two lines of luminaries in two-lane tunnels provide the best visual guidance to help drivers keep their lane and stay positioned below the correct luminary line. Two lines of lights will also give a feeling of space, both in width and height.
The use of LED lights in tunnels will give road users a visualisation of the alignment and more comfort. LED lights also allow users to drive closer to the tunnel walls, which is an advantage in bidirectional tunnels where drivers tend to drive towards the middle of the road, increasing risks of head-on collisions. In addition, LED lights increase the safety distance between vehicles.
Other light designs
Artistic lighting designs may also help reduce the road users’ anxiety and monotony in long tunnels. Nevertheless, artistic effects must be considered carefully because some artistic initiatives can give negative associations to the road user. For example, the use of art reminding road users of the fact that they are driving under water should be avoided in subsea tunnels. When planning the Oslo fjord tunnel, using naval elements in the decoration of the walls was suggested. After some discussion these suggestions were rejected because they would remind the drivers that they were driving in a subsea tunnel and thus increase anxiety.
Example of the Aurland-Lærdal tunnel in Norway
Also, artistic lighting designs must not remind of tunnel fires. The experiment with tunnel lighting design in the Aurland-Lærdal tunnel, conducted by SINTEF on a driving simulator, showed a design alternative with a combination of red, orange and yellow. This alternative provoked sudden brake reactions among participants, who found it frightening because it reminded them of a tunnel fire.
The 24.5 km long Aurland-Lærdal single-tube tunnel between Oslo and Bergen, opened in 2000, is the world’s longest road tunnel. SINTEF conducted a study aimed at suggesting initiatives to increase safety and comfort as well as reduce monotony. Dividing the tunnel into four sections by three rock caverns with lighting design was suggested. Three different alternative designs in addition to the alternative with no lighting design were tested in a driving simulator to evaluate the effect of each interior design in terms of road user behaviour, distraction, safety, perceived risk, comfort and reduction of monotony.
Objective parameters such as speed, lateral position, overtaking, stops and turning manoeuvres were continuously recorded. All verbal expression such as comments, sighs or outcries were also recorded. Subjective parameters were gathered by asking the participants after each test to fill in a questionnaire related to their specific experience with the tested alternative. The preferred alternative was the so-called “Rock crystals” design.
Then, an international competition among 10 artists, architects, light designers and film effect creators was launched. The three best ideas were converted to 3D simulator models and tested in the simulator before final selection. Finally an implementation process and on-site testing concluded the design. Click here to know more.
Example of the Zhongnanshan tunnel in China
The Zhongnanshan tunnel in Shaanxi province, close to Xi’an, opened in January 2007. At 18,020 metres, it is the world’s longest twin-tube road tunnel.Click here Based on knowledge and experience from the Aurland-Lærdal tunnel and transport safety in general, SINTEF was asked to optimize the design of the tunnel and to make it as safe and perfect as possible. Rock caverns with lighting design was recommended to contribute to a safer tunnel. Simulator trials were conducted at SINTEF in winter 2006. Three alternatives were presented to the participants, one of them without lighting design. The aim of the simulator trials was to test to what degree cavern lighting design can increase safety and attractiveness, and to what degree the lighting can reduce discomfort, anxiety and monotony. The results focused on cultural differences and anxiety
Both alternatives with special lighting in caverns were clearly ranked before the alternative without lighting. The so-called “Timetravel” lighting design was best rated but there were cultural differences in the preferences, where the Chinese preferred the “Skyway” design and the Norwegians preferred the “Timetravel” alternative.
Selecting the best alternative was difficult. The simulator study found no significant differences between lighting designs in terms of safety and monotony, whilst there were some significant differences within the subjective factors, sometimes in favour of one lighting design or the other. Two attractive and safe lighting designs were presented, and the selection of the final alternative was a question of taste. Click here to know more.
Assessing fears in the planned Rogfast tunnel in Norway
The Rogfast subsea tunnel is planned to be 25 km long and nearly 400 m deep to connect Stavanger and Bergen. SINTEF was asked to answer questions about safety and security in tunnels to know if a subsea tunnel is by nature more disadvantageous, what effect does the gradient have on security and are there differences between a gradient of 5, 7, 8 and 10%, if the length of the gradient has an effect on safety, if an intersection in a subsea tunnel is advantageous or disadvantageous, and are one or two tubes best in terms of security and discomfort. Click no/78. Visit www.sintef.no/content/page1____16224.aspx 30/07.
