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

Strategies to make the lighting installations of road tunnels more sustainable constitute a challenging line of research due to the difficulty of decreasing consumption and use of raw materials without impairing traffic safety. The first challenge when designing or optimizing these installations arises at the tunnel access, where the lighting requirements of the whole infrastructure must be determined as a function of several characteristics of the tunnel and its surroundings. This is the determination of the L20 luminance, that nowadays is still controversial due to the important differences between the methods established by the standards and regulations and the technical difficulties to implement them. In this work, a simple and safe method to easily calculate the L20 luminance in tunnels already open to traffic without expensive instruments nor risks for operators is presented. The equations to determine the radius of the L20 cone basis are developed and the potential errors analyzed. Some examples illustrate the methodology and validate it.