Abstract: The study shows that to a driver, the perceptible distance of a roadsign is inversely proportional to the speed of his car. The higher thespeed, the shorter the perceptible distance. Compared with walking pace,a car travelling at 100 kilometers an hour cuts down the perceptibledistance by 35-45%. Our experiment shows that this is possibly causedby the driver's psychophysiological stress when driving at speed.

Key words: NULL