The energetic impact of the lighting system in the road tunnels

The quantity of artificial light necessary in a road tunnel depends on the external luminance, the climatic conditions, the road surface wet or dry, the traffic speed, and the related safe driver stopping distance. The design of the lighting system takes into account these parameters, assuming critical conditions. This may result in very high electrical power demand. The authors, based on the experience acquired as a result of some designs made for Italian motorway tunnels, suggest a practical method to estimate the load demand and the annual energy cost for the proposed lighting system. It highlights the impact of the presence of a control system able to improve the safety and comfort for the drivers, avoiding the excesses of luminance and mitigating the energetic cost. The control has to operate and tune automatically the luminous flux emitted by the lighting system according to actual conditions given by the input signals of the external luminance, the climatic condition, and the traffic intensity.