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New, safer and cheaper method designed for determining the lighting requirements of road tunnels

Researchers from the University of Granada have developed a new, easy‑to‑implement method especially useful for those tunnels that are already open to traffic and whose installations need some kind of renewal

The economic, energetic and environmental impact of lighting installations of road tunnels is huge: the bill for even not excessively long tunnels may sum up to hundreds of thousands of euros per year in lighting consumption

Researchers from the University of Granada (UGR) have designed a new methodology, safer and cheaper than the one currently used, for determining the lighting demands of road tunnels. Their work is especially useful in tunnels already open to traffic and whose installations need some kind of renewal.

The economic, energetic and environmental impact of lighting installations of road tunnels is huge. The bill for even not excessively long tunnels may sum up to hundreds of thousands of euros per year in lighting consumption. And in addition, there’s the effect on the consumption of raw materials, the installation costs, and the emission of greenhouse gases derived from manufacturing and installing the hundreds of lamps necessary for each tunnel.

Above figures are truly worrying if we take into account that, only in Spain’s road network, there are more than 500 tunnels without counting underground passages, which depend on local administrations. It is, therefore, a problem of great magnitude.

Paradoxically, energy consumption in tunnels is much higher during the day than during the night, since during daytime hours lighting levels must be especially high in order to make the drivers’ visual adaptation easy. If the transition from a sunny exterior to a poorly lit interior was sudden, the decrease in visual capacity due to the slow adaptation of the human eye would be unacceptable, if we consider that a vehicle traveling at 100 km/h is traveling almost 28 m per second. This means that even the slightest delay in visual reaction time would result in tens of meters of uncontrolled progress.

The solution for achieving an acceptable visual adaptation is providing the tunnels with a powerful lighting installation, especially in the first hundred meters, and make it work at maximum power during the hours with high external luminance. The problem with this solution is the previously mentioned impact.

Currently, there are research groups in several countries which are actively working on strategies to reduce energy consumption of lighting installations in tunnels. The solutions that are beginning to be implemented range from the introduction of solar light inside the tunnels to the forestation of tunnel accesses with certain plant species with low reflection coefficient, as well as the gradual introduction of LED projectors in those tunnel sections (not all) where it is possible and feasible. As a result of these studies, the lighting installations of many tunnels are currently being renovated.

Those renewal operations require a prior assessment of lighting requirements for each tunnel, which in many cases have changed since the day they were open to traffic. To carry out said assessment, it is necessary to have very accurate images of the portal gates taken under controlled conditions stipulated by current standards and regulations. However, in tunnels already open to traffic, the requirements of said regulations are very difficult to implement in an accurate way while keeping the operators in safe conditions.

An easy‑to‑implement method

The research carried out by UGR professors Antonio Peña and Juan Carlos López presents a rigorous yet easy‑to‑implement methodology for using vehicle based photographs and even maps taken from internet (such as Google Street View, for example) with results equivalent to those of the current, strict methodology.

At present, due to traffic, the approximations taken give rise to considerable errors. The impact on the safety of the operators and on the accuracy of the calculations is very positive thanks to the new method, and it allows to safely carry out the necessary operations to renovate lighting installations in tunnels.

“This is very important in tunnels already open to traffic and whose lighting installations need to be renewed,” UGR professor Antonio Peña, lead author of this work, explains. “This is increasingly more frequent due to the gradual entry of LEDs in tunnel lighting. Nowadays, operators can not take clear photos from the distance and height strictly determined by the standard, pointing to a specific point of the tunnel access and in the center of the road. Due to the enormous danger that this entails, these photographs are currently taken from the shoulder (also very dangerous) and from approximate distances, which causes an error in the measurements. Our methodology provides some rescaling factors that convert the photos taken from vehicles in equivalents to those recommended by the standard, in tunnels already open to traffic.”

Bibliographic reference:

J.C. López and A. Peña-García. “Determination of lighting and energy demands of road tunnels using vehicle based photographs of the portal gates: an accessible and safe tool for tunnel renewal and maintenance,” Tunnelling and Underground Space Technology, 78, 8-15, 2018.

DOI: https://doi.org/10.1016/j.tust.2018.04.015

Images:

UGR researchers Antonio Peña and Juan Carlos López, authors of this study

Necesidades lumínicas de un túnel

A well‑lit tunnel

Contact info:

Antonio Peña García

Departamento de Ingeniería Civil de la UGR

Phone number: (+34) 958 249 435

E‑mail: pgarcia@ugr.es