Headlight glare in police-reported crash data: Prevalence, contributing factors, and potential effects

This study investigates the prevalence and contributing factors of headlight glare in police-reported crash data across 11 U.S. states from 2015 to 2024. The purpose was to evaluate the degree to which glare is reported as a contributing factor in nighttime crashes and to identify conditions and populations most commonly associated with glare.

Rates of reported glare in all crashes were calculated across sun-altitude categories. Glare in nighttime crashes was examined using crash data combined across multiple states, matched-pair comparisons within states, and narrative reviews of officer reports.

Glare was reported in only 0.1%-0.2% of nighttime crashes, with little variation over time despite the widespread improvement in headlight visibility that took place during the study years. Overall, most glare-related crashes occurred during daylight hours when the sun was close to the horizon. Nighttime glare crashes were disproportionately associated with older drivers, older vehicles, and undivided low-speed roads. Narrative analysis revealed that lane departures were the most common driver response to headlight glare, accounting for over half of cases.

While already at a low reported level, the results suggest the effect of headlight glare on crash risk could be further reduced by targeted countermeasures such as adaptive lighting systems, improved lane markings, and more advanced lane departure technologies. Additionally, future research should explore whether increased visibility from better illumination reduces drivers' susceptibility to glare from other vehicles. Previous research has demonstrated that improved headlight visibility reduces the risk of single-vehicle nighttime crashes. This study found no indication that such improvements have led to an increase in glare-related crashes.