The Relation between and Driving Behavior Discomfort Glare

Theeuwes, Jan; Alferdinck, Johan W A M · 1996 · ROSA P / United States. Department of Transportation. National Highway Traffic Safety Administration

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Summary

This study investigates the relationship between discomfort glare from oncoming vehicle headlamps and actual driving behavior, aiming to validate the widely used De Boer rating scale for measuring discomfort. The research was motivated by the need to determine whether headlamps that cause subjective discomfort, without necessarily impairing vision through disability glare, lead to unsafe driving behaviors. Additionally, the study sought to identify acceptable upper limits for glare illuminance to inform potential international harmonization of low-beam headlamp standards between the US and Europe. The experiment involved 24 subjects divided into three groups: young US drivers, young Dutch drivers, and older Dutch drivers. Participants drove an instrumented vehicle at night along a 23.5 km track comprising urban, rural, and highway sections. A simulated light source mounted on the vehicle’s hood replicated oncoming headlamp glare at intensities of 350, 690, or 1380 candela (cd), corresponding to European and US standard maximums, or remained off as a control. Researchers measured driving behavior, including speed, steering wheel reversals, gas pedal reversals, and object detection distances, alongside subjective discomfort ratings using the De Boer scale and other metrics. Results indicated that subjects adapted their behavior in a safe direction when exposed to glare. On dark and winding roads, drivers significantly reduced their speed and increased steering effort when the glare source was active, particularly at the higher intensities of 690 and 1380 cd. However, these higher intensities also caused a significant drop in object detection performance, increasing the number of missed targets and reducing detection distances. Older subjects exhibited the largest behavioral adaptations and the most significant declines in object detection. Crucially, the study found no correlation between De Boer discomfort ratings and actual changes in driving behavior; high subjective discomfort did not predict larger speed reductions or poorer detection performance. The findings suggest that drivers compensate for glare by slowing down and increasing effort, maintaining safety despite reduced visual performance. Because this safe behavioral adaptation occurred independently of the specific glare illuminance within the tested ranges, the study concludes that a glare illuminance of at least 1.1 lx (equivalent to the US standard of 1380 cd) is acceptable as a maximum upper limit. However, the authors note that on dark roads, any glare illumination will degrade object detection. The lack of correlation between subjective ratings and behavioral changes implies that the De Boer scale may not be a reliable predictor of driving performance impacts, challenging its utility for setting safety standards.

Key finding

Drivers adapted to discomfort glare by reducing speed and increasing effort, but this behavioral adaptation was not correlated with subjective discomfort ratings, while higher glare intensities significantly reduced object detection performance.

Methodology

on_road

Sample size: 24

Provenance

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Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified_with_issues.

Topics

Ranked by relevance to this paper. Hover a topic for its definition.

• discomfort glare
• disability glare
• visibility analysis litigation
• dark adaptation mesopic
• sensory abilities
• visual

Information type

What kind of knowledge this paper contributes, grouped by family — independent of topic (what it is about) and method (how it was studied).

• Empirical Findings: behavioral performance data
• Methodological Resource: measurement protocol