Abstract
A road tunnel is an enclosed and covered infrastructure for the vehicular traffic. Its lighting system provides 24 h of artificial sources only, with a higher amount of electric power used during the day. Due to safety reasons, when there is natural lighting outside the tunnel, the lighting levels in the stretches right after the entrance and before the exit must be high, in order to guide the driver’s eye towards the middle of the tunnel where the luminance must guarantee safe driving, avoid any over-dimensioning of the lighting systems, and produce energy savings. Such effects can be reached not only through the technological advances in the field of artificial lighting sources with high luminous efficiency, but also through new materials for road paving characterized by a higher reflection coefficient than other ordinary asphalts. This case study examines different technical scenarios, analyzing and comparing possible energy and economic savings. Traditional solutions are thus compared with scenarios suggesting the solutions previously mentioned. Special asphalts are interesting from an economic point of view, whereas the high costs of LED sources nowadays represent an obstacle for their implementation.
Highlights
Lighting systems are designed to ensure that the vehicular traffic traverses the road tunnel in the most comfortable and safe way possible, aspiring to have the same conditions that characterize the zones preceding and following the tunnel
The interior zone of the tunnel must have a minimum amount of lighting [2,3] to allow safe driving without overloading energy consumption and management costs
The lighting of road tunnels, defined by the regulations as “long”, requires high luminous fluxes and this implies a high energy consumption due to the electric power used by the artificial light system
Summary
Lighting systems are designed to ensure that the vehicular traffic traverses the road tunnel in the most comfortable and safe way possible, aspiring to have the same conditions that characterize the zones preceding and following the tunnel. Lighting a tunnel becomes even more onerous when there is high luminance outside the structure. For this reason, the tunnel lighting system consumes more electric power by day, especially during the summer months, with the longest time intervals between dawn and dusk determining higher luminance levels outside the structure due to an apparent higher sun position and clearer skies. In accordance with the current regulations [4,5,6], to avoid a decrease of the drivers’ visual perception while passing from the outside (highly illuminated due to solar radiation) through to the inside of the tunnel with a different lighting level, it is necessary to realize a illuminated zone in the tunnel (threshold zone + transition zone, complying with CIE 88 [2]) which introduces the drivers to the new conditions of visual perception they will find inside the tunnel
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