Improving the Effectiveness of Nighttime Temporary Traffic Control Warning Devices, Volume 2: Evaluation of Nighttime Mobile Warning Lights

Vehicle-mounted warning lights for nighttime mobile highway operations provide critical protection to workers and the driving \npublic. Alerting the traveling public of the approaching work activity and providing guidance is vital to maintaining safety and \nmobility. Previous research conducted for IDOT on mobile lane closures (Steele and Vavrik 2009) identified driver confusion \nas a concern to the safety of nighttime highway operations. Users are subject to warning lights from multiple agencies with \nvarying characteristics and configurations, but we know little about driver comprehension of these signals and their influence \non driver behavior. \nApplied Research Associates, Inc. (ARA) studied the effectiveness of warning lights on nighttime highway operations, \nincluding mobile lane closures, incident responses, and police activities, by reviewing pertinent literature, performing \nobservational and experimental field studies, and conducting driver surveys and focus groups of driver perceptions and \nbehavior in response to nighttime mobile operations. We used a cognitive model of driver mental processes to analyze this \ninformation and better understand the interaction between warning lights and driver perception and behavior, and to identify \nand evaluate potential improvements to current practice. \nThe research showed that drivers view current vehicle-mounted warning lights as highly visible, attention-getting, and \neffective at conveying the message caution/alert. However, intense lights can cause discomfort glare and multiple light sets \non individual vehicles, or multiple vehicles at a location, can be distracting, annoying, or anxiety-inducing. Complex visual \nscenes can confuse drivers and take longer to process cognitively, leading to slower reaction times. Often, information \nprovided by flashing arrows, signs, and changeable message signs can be interfered with by other warning lights on the same \nvehicle. \nSuggestions for improvement from the focus groups centered primarily on reducing the number of flashing lights, or \nsynchronizing their flashing, on individual vehicles, reducing the intensity of specific lights, sequential flashing of arrows \nbetween multiple trucks in a convoy, and incorporating directional motion in light bars. Researchers were not able to test \nsome of the ideas due to limitations of current device technology; however, field experiments on several suggested concepts \nshowed the potential to improve driver perception, comprehension, and behavior by modifying the number, intensity, and \nsynchronization of lights on individual vehicles, as well as between vehicles.