Traffic signal brightness: an examination of nighttime dimming; final report

This report documents the procedures and findings of a study to determine the traffic operations, safety, and economic impacts of dimming traffic signals at night. A laboratory experiment was conducted to measure how quickly and accurately elderly and color vision-deficient drivers responded to signals dimmed to as low as 12.5 percent of ITE recommendations. Controlled field experiments evaluated driver responses to 8-1inch and 12-inch signals dimmed to as low as 10 percent of ITE recommendations, seen against simple, moderate and complex backgrounds. Observational field studies confirmed that drivres behaved safely and efficiently when signals were dimmed to as low as 30 percent of ITE recommendations. Economic analysis indicated that simple dimming arrangements can repay the initial investment within 3 years and save about 10 percent in energy. Guidelines are recommended for selecting intersections for dimming and for initiating/terminating dimming in the morning and evening. (Author)