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The anti-glare facilities in median strips are designed to block opposing headlights in order to avoid disability glare, but a large amount of headlight leakage results in uncomfortable glare, to the point that drivers can barely detect dangerous obstacles or road conditions. This paper aims to explore the glare range under high-beam headlights on drivers’ visual requirements. Based on an analysis of the mechanism of headlight glare, this paper proposes a subjective headlight glare scale, and classifies glare discomfort into two categories: interference glare, and acceptability glare. Combining the scales, 24 drivers and a standard light-emitting diode automotive headlamp were used to conduct glare effect tests. The size of the laboratory that closes to scotopic vision is 12 m × 6 m. The illuminance thresholds of disability glare–interference glare (DGIG) and interference glare–acceptability glare (IGAG), along with the spatial distribution of each glare level, were collected at the longitudinal distances of 3 m, 5 m, 7 m, 10 m, and 12 m. Meanwhile, the illuminance threshold and the spatial distribution of each glare level up to a longitudinal distance of 120 m were calculated. The results indicate that disability glare is distributed in the central area, while interference glare and acceptability glare are distributed from the center to the margins. At the same longitudinal distance, the vertical illuminance of the driver’s eye under the same glare level is almost equal. In the range of a longitudinal distance of 120 m, the spatial distribution of each glare level enlarges with each increase in longitudinal distance. The results can provide scientific evidence for calculating the reasonable heights of anti-glare facilities for expressways with different alignments.

Glare comes from natural or artificial light that affects the driver's ability to identify obstacles in front of the road and road driving conditions, which endangers the safety and comfort of driving and causes traffic accidents. At present, the theoretical basis of glare only considers the interaction between glare sources and human eyes. The evaluation methods and prevention measures of glare mainly focus on disability glare, which cannot use to evaluate glare in road traffic. It should be relative to road traffic scenarios and driving task requirements. This paper analyzed the types and characteristics of glare sources in road traffic, the characteristics of a standard target for visual recognition, and the visual condition and driver demand in driving tasks. The mechanism of glare in road traffic was obtained by analyzing safe and comfortable driving. The interaction among glare sources, standard target, and the driver was studied. A subjective scale was proposed for the glare in road traffic. The results can provide a theoretical basis for the measurement methods and evaluation of glare in road traffic and anti‐glare in road traffic technology.