Abstract
The experiment investigated the ability of subject drivers to perform a two-lane passing task, with oncoming traffic, as a function of the level of ambient illumination and the headlight intensity of the oncoming vehicle.
Eight experienced drivers performed both passing trials and gap-estimation trials, under closed-course conditions, during dawn and dusk hours. Levels of ambient illumination varied from approximately .02 to 200 foot candles during the experiments. Headlight conditions included no lights, normal low-beam headlights and low-beams with filters which reduced their intensity to about 1/3 of normal.
Results indicated that the gaps accepted by drivers in a two-lane passing situation increased with an increase in the intensity of the headlight of the oncoming vehicle. The range of gaps accepted across headlight conditions was smaller, however, at higher levels of ambient illumination than at lower levels. Best results in terms of mean gaps accepted and minimum variability in performance was achieved with the reduced intensity low-beams. Results are discussed in terms of the optimum intensities of daytime running-lights. Suggestions for future research are presented.
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