Traffic Signs and Real-World Driver Interaction

Abstract

The purpose of this field study was to compare nighttime traffic sign legibility under static (parked) and dynamic (driving) conditions using bottom-up legibility as a measure of performance. Drivers need more traffic sign luminance to recognize words on signs while driving than they need when sitting still (parked). The primary reason for this increase in luminance demand is that the driver must periodically shift visual attention away from the sign to attend to the driving task. Legibility performance was assessed with N = 18 observers driving at an assigned speed of 48 km/h (30 mph). Participants ranged in age from 55 to 77 with a mean of 66 years. At a distance of 36 m (120 ft) there was a 117% increase from the static to the dynamic demand luminance. At a longer distance of 55 m (180 ft), there was a 256% increase, and at a distance of 57 m (187 ft), the increase was 556%, and beyond that distance, we could no longer generate a luminance that was sufficient to meet the dynamic demand.