Proposal to forest Alpine tunnels surroundings to enhance energy savings from the lighting installations. Towards a standard procedure

The lighting installation in tunnels is a major problem in terms of drivers safety, energy consumption and use of raw materials. According to the recommendations of the International Commission on Illumination (CIE), the demand of tunnels in terms of luminance mainly depends on three factors: maximum speed allowed inside the tunnel, tunnel orientation and the characteristics of the portal gate surroundings. Focusing on this last factor, this study analyses how changes in the vegetation of the portal gate surroundings in an Alpine environment can contribute to save energy from the lighting installation. Its main target is to achieve a low L20 luminance through the lowest reflectance of portal surroundings, which is connected to a minor luminance requirement inside the tunnel. Departing from several autochthonous species growing in that climatic zone, photometrical considerations are introduced in order to find the most accurate one to maximize savings without impairing the safety. It has been concluded that common ivy is the most suitable specie to forest the entrance of the tunnels in Alpine zone, allowing decreases in the installed power between 22 and 53 kW in the tunnels considered in this research. The accuracy of common ivy is specially relevant because other research based on completely different environments and climates also concluded that this specie is the best in terms of energy and installed power savings. These data show that a standard procedure based on climbing species like common ivy can allow the achievement of more sustainable road tunnels.