Nighttime Glare and Driving Performance: Research Findings

In 2001, NHTSA opened a public docket requesting comments from the public regarding headlamp glare. Most responses received have been complaints. NHTSA initiated research to address these complaints and to determine causes and effects of headlamp glare. In 2005, Congress authorized NHTSA to "conduct a study on the risks associated with glare to oncoming drivers, including increased risks to drivers on 2-lane highways, increased risks to drivers over the age of 50, and the overall effects of glare on driver performance" including "recommendations regarding measures to reduce the risks associated with glare to oncoming drivers." This report summarizes research on headlamp performance, visibility, glare, and safety conducted to address the issues identified by Congress and by NHTSA through review of public comments. These research activities included a state-of-knowledge report; a pilot study using naturalistic methods to assess relationships among glare, driving behavior and crash risk; analyses to compare the effects of headlamp characteristics on visibility and glare; preliminary assessments of headlamp illumination and aim on real-world lighting conditions; a review of visual needs regarding visibility and glare and metrics for characterizing them; a field experiment to characterize recovery of older drivers following exposure to headlamp illumination; and demonstration of a prototype safety-based adaptive forward-lighting system with potential to reduce glare while maintaining visibility, by decreasing intensity toward nearby drivers.