LEGIBILITY OF TRAFFIC SIGN TEXT AND SYMBOLS
operations - traffic
Traffic signs, Traffic sign legend, Symbols, Reflective signs, Night, Lettering, Legibility, Instructions, Human subject testing, Highway signs, Field studies, Distance, Daylight
An exploratory daytime and nighttime sign recognition and legibility field driving experiment involving 11 new reflectorized right-shoulder-mounted traffic signs and 10 young, healthy subjects (three replications) is described here. It was hypothesized that daytime conditions would provide longer recognition and legibility distances than nighttime conditions and that signs with bold symbols would provide longer recognition and legibility distances than textual signs. Also of interest was the formulation of the instructions to the subjects, which is likely to influence the legibility and recognition distances. Whereas other researchers have encouraged subjects to guess the symbols or legends, it was emphasized in the instruction of this experiment that the subjects were to say aloud the information on the traffic signs at that point during the approach when they could clearly (with near 100% certainty) identify all visual details of the message or the symbol. By comparing these results with the results of other studies, it was found that legend and symbol identification under clearly seen conditions provides legibility and recognition distances that are considerably shorter than those obtained if guessing is allowed. The average daytime legibility and recognition distances were about 1.8 times longer than the average nighttime legibility and recognition distances. It may be tentatively concluded that when reporting on field legibility research, it is of utmost importance to provide the reader with detailed information about how the subjects were instructed to respond to the stimuli (e.g., guessing was allowed versus clearly seen message). From the data obtained in this study, it appears that the effect of the subject instruction formulation is stronger under nighttime low-beam conditions than during daytime.
Zwahlen, H, Schnell, T. (1999). LEGIBILITY OF TRAFFIC SIGN TEXT AND SYMBOLS. Transportation Research Record, Vol. 1692, p. 142-151.