Recognition of Traffic Sign Symbols in the Field during Daytime and Nighttime

Abstract

Early recognition of Traffic Control Devices, especially the recognition of symbols on warning signs is important since this provides drivers with a maximum amount of time to make decisions with regard to vehicle direction, speed and lateral position. A number of studies providing recognition distances for selected traffic warning sign symbols have been published in recent years. All these laboratory studies provide relatively short recognition distances. Independent daytime and nighttime field experiments for traffic warning sign symbol recognition were conducted using a set of 12 retroreflective warning signs. The results indicate that the average symbol recognition distances obtained in this study for daytime conditions are about 2 times longer than the corresponding distances obtained in the laboratory and are about 1.2 times longer than the corresponding nighttime distances obtained in this study. The 50, 85, 90, 95 and 99 percentile symbol recognition distances have been established for both daytime and nighttime field conditions. Based upon the results of this study it may be tentatively concluded that in spite of the slight distance reducing influence of the transmissivity of the atmosphere in the field studies, the laboratory studies produce much shorter symbol recognition distances and that these distances obtained in the laboratories have a highly questionable validity when used in accident reconstruction studies or as absolute design values in the real world.