Distance perception of vehicle rear lights in fog

Perceptual difficulty is one of the main explanations given for the behavioral modifications and high accident rate associated with driving in fog. The present study investigates how fog and the characteristics of vehicle rear lights affect distance perception. Two experiments in a fog chamber (meteorological visibility range of 5-15 m) were run under conditions simulating nighttime fog. The participants gave verbal estimates of the distance (8-28 m) of vehicles simulated by rear-light arrangements. The results revealed an average increase of 60% in the perceived distance of vehicles in fog as compared with normal visibility conditions. Distance overestimation was particularly pronounced when the vehicle had only 1 fog light instead of 2 and when the lights were close together. No effect of light height was observed. These results suggest that the perception of vehicle distance in nighttime fog could be significantly improved by the presence of 2 lights with maximal spacing. Actual or potential applications of this research include vehicle rear light design.