Three sets of experiments were conducted. Two were under highway conditions and one used a laboratory device simulating roadway conditions. Variations in headlight beams, both impinging and opposing, were introduced in the laboratory study. Comparisons of the two show similar relative results for laboratory and road studies when distances set for experimental study are taken into account. Visibility of a lead vehicle was varied by using different sizes and intensities of tail-gate treatment with one and two taillights used as a standard of reference. Surfaces having high-reflection characteristics were found to decrease the time and difficulty for the discrimination of relative speeds between vehicles. The higher intensities did not show as great an increase in time and difficulty when the size of the tailgate surface was decreased. Certain other beneficial effects of high-contrast treatment are shown when variations of opposing and impinging headlight beams were used. It was concluded that a decrease in the amount of over-all illumination increased the time, and difficulty and distance judgments for conditions of relatively low visibility. High-beam opposing lights reduced the visibility from the increase in perception or judgment time for the high levels of contrast, and the decrease in threshold distances for other experimental conditions. The use of materials giving greatest visibility and perceptual value at night significantly decreased the time and difficulty for discriminating speed differentials in most cases studied. High perceptual values of vehicles and other objects on the highway establish a significant safety factor at night.
Samenvatting