A new metric to predict flicker effect in long tunnels and underground roads

The flicker effect can be roughly defined as the visual perception of a change in luminance or spectral distribution with time. It can happen in a wide variety of situations but has a peculiarity in tunnels: the changes in the light pattern are not due to the source, but to the movement of the vehicles. In parallel, the new technologies and trends to build very long tunnels and underground roads (VLUR), where drivers stay longer, give a key role to the flicker effect. These circumstances, together with the serious consequences of lower performance and the severity of accidents in tunnels, require effective strategies to predict, quantify and minimize it. In this work, the characteristics and peculiarities of this effect in tunnels are analyzed and, departing from this framework, a new metric to assess the newly defined Flicker Frequency referred to HPD Overlap (FHO) and the potential flicker even before the installation is working, is developed. The methodology in this work has combined both theoretical considerations and calculation of the typical parameters for the main zones of the tunnel.