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 public. Alerting the traveling public of the approaching work activity and providing guidance is vital to maintaining safety and mobility. Previous research conducted for Illinois Department of Transportation (IDOT) on mobile lane closures (Steele and Vavrik 2009) identified driver confusion as a concern to the safety of nighttime highway operations. Users are subject to warning lights from multiple agencies with varying characteristics and configurations, but  researchers know little about driver comprehension of these signals and their influence on driver behavior.

Applied Research Associates, Inc. (ARA) studied the effectiveness of warning lights on nighttime highway operations, including mobile lane closures, incident responses, and police activities, by reviewing pertinent literature, performing observational and experimental field studies, and conducting driver surveys and focus groups of driver perceptions and behavior in response to nighttime mobile operations.  Researchers used a cognitive model of driver mental processes to analyze this information and better understand the interaction between warning lights and driver perception and behavior, and to identify and evaluate potential improvements to current practice.

The research showed that drivers view current vehicle-mounted warning lights as highly visible, attention-getting, and effective at conveying the message caution/alert. However, intense lights can cause discomfort glare and multiple light sets on individual vehicles, or multiple vehicles at a location, can be distracting, annoying, or anxiety-inducing. Complex visual scenes can confuse drivers and take longer to process cognitively, leading to slower reaction times. Often, information provided by flashing arrows, signs, and changeable message signs can be interfered with by other warning lights on the same vehicle.

Suggestions for improvement from the focus groups centered primarily on reducing the number of flashing lights, or synchronizing their flashing, on individual vehicles, reducing the intensity of specific lights, sequential flashing of arrows between multiple trucks in a convoy, and incorporating directional motion in light bars. Researchers were not able to test some of the ideas due to limitations of current device technology; however, field experiments on several suggested concepts showed the potential to improve driver perception, comprehension, and behavior by modifying the number, intensity, and synchronization of lights on individual vehicles, as well as between vehicles.