Assessing Daylight Penetration in Short Tunnels for Enhanced Driver Safety: A 2-D Numerical Model

Recent studies have highlighted a disparity in accident frequencies between short and long tunnels, challenging the prevailing assumption that natural daylight adequately permeates shorter tunnels to ensure visibility. This discrepancy has underscored a critical need for national guidelines regarding the necessity and extent of artificial lighting in short tunnels, as insufficient illumination in such settings poses a significant safety hazard. However, the blanket application of artificial lighting across all short tunnels is neither cost-effective nor practical. To address this issue effectively, it is imperative to comprehensively assess natural daylight penetration in short tunnels prior to considering artificial lighting installations. In response to this pressing concern, our study presents a simple two-dimensional numerical model designed to accomplish this objective. This model takes into account key input parameters, including portal illuminance and the physical attributes of the short tunnel, such as its length and height. The model's output provides a valuable insight into horizontal spatial illuminance levels within the tunnel. Validation of our numerical model was conducted using field data collected from 16 tunnels in Georgia, demonstrating a remarkable degree of consistency between the simulated results and the actual field measurements. However, we duly acknowledge the limitations of this simplified approach, which does not capture variations of illuminance caused by factors such as shadows at the portal and exit, reflective properties of surfaces, geometry variation in the width such as presence of wall and piers, etc. Nonetheless, this numerical model serves as a starting point to spur further research on daylight penetration in short tunnels, with the goal to improve the safety for all tunnel users.