Practical research into tunnel lighting

Previous studies and tests on making tunnel lighting more sustainable show that there are various possibilities for further reducing the energy consumption of lighting in tunnels. However, additional research is needed to better substantiate and further concretize the various options. For example, to see if the savings measures also work in other tunnels. The COB has developed a research program for this, together with several parties, including Rijkswaterstaat.

The COB is looking for tunnel projects at home and abroad to carry out this research program. Interested parties can apply to the COB for one of the fourteen research projects listed below.

1. Reducing light levels in basic lighting and entrance lighting

Of interest to: managers of tunnels with high-pressure sodium lamps and managers of tunnels with LED lighting.
Various experiments indicate that the wider light spectrum of LED lamps allows for a reduction in light levels of between 30 and 50 percent, without negatively affecting perceptions. The current lighting level guideline is based on the use of narrow-spectrum high-pressure sodium lamps. In order to review this guideline and determine the best objects to observe, the plan is to carry out reference measurements in tunnels equipped with high-pressure sodium lamps.
A test panel consisting of lighting experts, tunnel safety experts, administrators, and tunnel users of different ages will be formed for these measurements. The test panel will assess the visibility of the objects from moving vehicles at different speeds. Subsequently, the panel will examine the lighting level at which the objects are equally visible in one or more tunnels with LED lighting. This can be done for both the basic lighting and the entrance lighting. If several tunnels show that the lighting level of LED lamps for the basic and/or entrance lighting can indeed be reduced, the guideline can be adjusted.

2. Reduction of the basic lighting level in long tunnels

Of interest to managers of tunnels longer than 1500 meters.
In the Netherlands, a minimum light level has been established for basic lighting. Since the human eye adapts quite rapidly to less light, it is expected that the light level in the central zone of long tunnels can be reduced further. This is already happening in tunnels abroad. The proposal is to examine the extent to which this measure is feasible in specific tunnels. Guidelines from other countries can also be studied. If lowering the light level seems possible, the plan is to carry out some practical tests in long tunnels.

3. Dynamic control of light level in the entrance area based on actual speed

Of interest to managers of existing or new tunnels with LED lighting.
The light level of the entrance lighting is gradually reduced over a specific distance on the basis of the so-called CIE curve. Until now, the CIE curve has been determined on the basis of the design speed (the maximum speed at which cars can drive safely through the tunnel). The light level is set in such a way that a motorist driving at this speed can look far enough ahead and stop in time at any obstacle on the road. The design speed is often higher than the actual speed in the tunnel. At a lower speed, the braking distance is shorter and the light level from the tunnel entrance can be reduced sooner. The plan is to research how much energy can be saved if the entrance lighting is controlled on the basis of the actual speed of the traffic. This can be done in a practical test. Two options are considered: lowering the light level according to a number of fixed steps (e.g. 100, 90, and 70 kilometers per hour) or fully dynamic control of the light level.

4. Smoother progression of the CIE curve

Of interest to managers of tunnels with LED lighting.
The CIE curve which is used to date was established in the 1960s on the basis of simple laboratory research. The expectation is that this curve can progress more smoothly, without the current discontinuities, which can result in significant energy savings. A smoother curve is in use in various tunnels in Italy. Unfortunately, no scientific evidence is available for now to support this. We plan to carry out road tests to assess whether a smoother curve for the entrance lighting has no adverse effects on safety.

5. Application of new curve for eye sensitivity in light measurements

Of interest to managers of tunnels with LED lamps that can vary in color or parties with laboratory settings.
The current measuring equipment, which measures the amount of light in tunnels, is based on a light sensitivity curve that was established a long time ago, in the 1930s. There is now a new curve that better matches the way the eye perceives light. It appears that eyes perceive more light, particularly in the blue part of the light spectrum. This new curve also corresponds better to the light spectrum of LED lamps. Because LED lamps emit a relatively large amount of blue light, people perceive more in LED lighting than what the lux or luminance meter measures. When the sensitivity of the measuring equipment is adjusted to better correspond to that of the human eye, the light level of LED lamps – and therefore the energy consumption – can be reduced without compromising safety. Since people’s fully opened pupils (in darkness) are mainly sensitive to blue light and their largely closed pupils (in bright light) are mainly sensitive to red light, it is worth considering making the light in the central part of tunnels bluer and the light at the entrance redder. To get a better idea of the potential of this energy-saving option, we need, besides scientific research, to set up a test with dimmable LED lamps whose light color can be changed (as in the Mont Blanc tunnel).  Such LED lighting is being used in the renovation of the Kiltunnel. The color temperature of this lighting can be varied between neutral white and cold white. This makes this tunnel, in principle, suitable for this research project.

6. Use of highly reflective asphalt

Of interest to managers of new tunnels or existing tunnels where the asphalt needs to be replaced.
Following research, the consortium used light-colored asphalt, which reflects light better, in the Gaasperdammertunnel. This allows the light level in the tunnel to be reduced and achieves a 20 percent saving in electricity consumption. It is expected that highly reflective asphalt can also lead to considerable savings in other tunnels. The plan is to have the research, which was carried out at the Gaasperdammertunnel, reviewed by a lighting expert and to have a table of reflection values drawn up for various types of asphalt. We are also looking for tunnel projects that want to research whether a business case with highly reflective asphalt is possible. We see two options here: using reflective asphalt in the entire tunnel or only in the entrance area.

7. Controlling basic lighting according to traffic intensity and speed

Of interest to managers of tunnels with widely varying traffic intensities and speeds.
The light level of the basic lighting in tunnels is determined in the design stage. Important factors include the design speed and the expected traffic volume. High design speeds and heavy traffic require a higher light level than lower design speeds and little traffic. In practice, the design speed is often higher than the prevailing speed limit, which leads to a light level that is higher than necessary. Furthermore, the actual speed and/or intensity of traffic are found to be lower than the design values for part of the time. By adjusting the light level according to the actual traffic speed and intensity, electricity consumption can be reduced. The plan is to calculate the savings potential of automated control of the light level based on actual traffic data and – if the potential is sufficiently great – to carry out a trial with such control in existing tunnels.

8. Better monitoring of tunnel lighting control

Of interest to managers of existing tunnels.
In many tunnels, the lighting controls do not work properly. For example, on sunny days the level of entrance lighting is too low and on cloudy days it is too high. It also happens that on summer evenings the lighting switches to night mode too early or that all the lights appear to stay on at night. Errors of this kind can have many causes: the L20 light sensor faces the wrong direction, a control clock is set incorrectly or there is some other malfunction. Unfortunately, such errors are not corrected quickly enough, if at all. Furthermore, in some cases, they lead to significantly higher energy consumption. A periodical check on the operation of the lighting control system can prevent errors or speed up repairs. The plan is to map out how monitoring can best be organized. We are, therefore, looking to cooperate with maintenance parties of existing tunnels to analyze the lighting control system in real-life conditions on the basis of log data of the control system and/or on the basis of practical observations. This may lead to improved maintenance instructions and adjustment procedures.

9. Limiting the lighting level by counteracting glare

Of interest to managers of tunnels with sunken road sections or with road sections with adjustable public lighting.
If glare from oncoming traffic is prevented, for example by using higher guide rails in the central reservation, the car’s headlights may be sufficient for a good view of the road and there may be no need for public lighting or much less of it. This can lead to significant energy savings. The problem of glare does not occur in Dutch tunnels, but it does on connecting sections or sections of the sunken road. We recommend that this measure should not only be investigated on regular roads, for example with road tests, but also on sunken roads that lead, for example, to a tunnel. We expect that in that case the light level of the tunnel lighting can be reduced at night.

10. Making the tunnel entrance greener

Of interest to managers of existing tunnels with space for greenery above the tunnel entrance.
The light intensity required in the entrance area of tunnels is determined by the light conditions when approaching the tunnel. To this end, the L20 meters also take into account the situation around the tunnel entrance, including the sky. Trees and shrubs above and next to the tunnel entrance can reduce the need for entrance lighting. The vegetation can block part of the (sun) light, causing the light level in front of the entrance to be lower. This is the case, for example, at the southern entrance to the Drechttunnel. The plan is to investigate, together with tunnel managers and maintenance parties, to what extent shielding the ‘sky’ can help to reduce the required light level.

11. Improving L20 measurements

Of interest to managers of existing tunnels and tunnels at the design stage.
L20 meters measure the light level right in front of a tunnel entrance. This measurement is used to control the lighting at the entrance to the tunnel. The meter is often placed in the central reservation at a certain height and distance from the tunnel entrance. Setting the L20 meter is specialist work and is usually only done when the lighting is installed. Maintenance and operation checks rarely take place, as this would require lanes to be closed in both directions (during the day) with the potential for considerable traffic disruption. As a result, L20 meters often malfunction in practice, resulting in the light level of the entrance lighting being too low or too high. To improve the functioning of L20 meters, it is necessary to investigate which parameters are important when setting them. It is also necessary to examine how maintenance and adjustment of each parameter are possible without hindering traffic. One possibility is to make it possible to adjust the meter remotely. It must also be investigated whether L20 meters can be made ‘zoomable’ in distance to the tunnel entrance so that the measuring area can be adjusted to the current driving speed. It will also be examined whether it is necessary to take measurements in the central reservation or whether we can come up with alternatives.

12. Ratio of reflection of walls and road surface

Of interest to managers of tunnels where the amount of light directed at the walls and road surface can be adjusted, or tunnels where different wall coverings are installed next to each other.
The light from the luminaires in the tunnel ceiling is directed at both the walls and the road surface. In the Netherlands, the regulation now stipulates that the brightness of the walls must be at least 60 percent of the brightness of the road surface. Research in the Mont Blanc tunnel has shown that road users see objects on the road surface best when the walls have the same level of reflection as the road surface. We intend to investigate whether this also applies to Dutch tunnels and which wall materials are the least prone to pollution or the best to clean so that the walls continue to reflect the light properly.

13. Advantages of line lighting compared to point lighting

Of interest to managers of existing tunnels with line lighting or point lighting.
Line lighting provides a higher quality of lighting than point lighting. For example, line lighting ensures a more uniform light level, less glare, a more even shadow gradient, and does not produce the so-called flicker effect This higher quality of lighting may make it possible to reduce the level of basic lighting in tunnels. This can be researched by carrying out tests in a number of existing tunnels and comparing the results.

14. Direct current tunnel lighting

Of interest to lighting developers/researchers.
The energy transition is leading to more and more electricity being produced in the form of direct current (DC). The conversion of direct current into alternating current involves energy loss. It is therefore worthwhile investigating whether tunnel lighting working off direct current is feasible, particularly since all sorts of components are already used in lighting systems that work of direct current perfectly well. Besides saving energy, switching to direct current also saves on materials, for example, because cables need not be as heavy.