Although visual performance was measured in terms of visual response timein many psychophysical studies, such approach was not used in evaluating the effect of luminance on traffic sign legibility performance. Traffic sign and retroreflective sign sheeting performance at night have been historically identified with the threshold (farthest) distance for legibility, and in many cases from stationary vehicles with no restrictions on viewing time. Since traffic signs are not always read at threshold distances or threshold luminances and since the time to read traffic signs are usually limited in the real world, a proper assessment of sign legibility performance requires determining information acquisition times above threshold conditions. This study investigated the effect of (legend) luminance and lettersize on the information acquisition time and transfer accuracy from simulated traffic signs. Luminances ranged from 3.2 cd/m2 to 80 cd/m2 on positive-contrast textual traffic sign stimuli with contrast ratios of 6:1 and 10:1, positioned at 33 foot/inch and 40 foot/inch legibility indices viewedunder conditions simulating a nighttime driving environment. The findingssuggest that increasing the sign luminance significantly reduced the timeto acquire information. Similarly, increasing the sign size (or reducing the legibility index) also reduced the information acquisition time. Thesefindings suggest that larger and brighter signs are more efficient in transferring their message to the driver by reducing information acquisition time, or alternatively, by increasing the transfer accuracy. In return, reduced sign viewing durations and increased reading accuracy is likely to improve roadway safety
Samenvatting