Traffic Sign Luminance Requirements of Nighttime Drivers for Symbolic Signs

Abstract

An experiment was designed to determine the luminance contrast and background luminance requirements for recognition of negative contrast symbol signs (black on yellow) under low-adaptation luminance conditions. The effects of background complexity (two levels), symbol type (four symbols), background luminance (five levels), and luminance contrast between the symbol and its immediate sign background (six levels) were studied. The experiment was conducted in the Traffic Sign Simulator Facility of the Operator Performance Laboratory at the University of Iowa. Participants walked toward a calibrated, fixed-size sign stimulus projected on a large projection screen in the study. Two levels of performance were assessed: maximum recognition distance (threshold) and the distance at which the symbol types could be recognized with ease (confident). A total of 40 subjects, half of whom were young and half older, participated in the study. The traffic sign background luminance, luminance contrast, and symbol type were found to be statistically significant in affecting the symbol recognition distance. Observer age and background complexity were statistically nonsignificant. The difference between the threshold and confident viewing distances was also significant. The recognition performance data of four symbols is presented in terms of the visual angles subtended by the heights of the symbols for the six levels of contrasts and the five levels of background luminances.