Legibility Distance of Variable Message Signs in Simulated Nighttime Fog for Elderly and Non-Elderly Drivers

Variable-message signs (VMS) are essential visual systems that convey roadway information to drivers; however, their legibility declines under foggy conditions. In this study, the effect of fog on VMS legibility was examined and legibility distances between elderly and non-elderly drivers were compared. Experiments were conducted in a facility capable of simulating foggy nighttime environments by measuring legibility distances for various display formats (symbols, numbers, and text) at varying fog densities. The results showed that heightened fog density significantly reduced legibility distance. Elderly drivers performed better with symbolic displays, whereas non-elderly drivers showed greater legibility for numeric and textual displays. Under dense-fog conditions, the minimum legibility distance requirements were not met, highlighting the need for luminance standards suitable for foggy conditions. These findings provide empirical evidence for improving VMS operation to foster safer driving environments, particularly for elderly drivers.