Effects of Emergency Vehicle Warning Lighting System Characteristics on Driver Perception and Behavior

Secondary crashes, including struck-by incidents are a leading cause of line-of-duty deaths among emergency responders, such as firefighters, law enforcement officers, and emergency medical service providers. The introduction of light emitting diode (LED) sources and advanced lighting control systems, provides a wide range of options for emergency lighting configurations. This study investigated the impact of lighting color, intensity, modulation, and flash rate on driver behavior while traversing a traffic incident scene at night. The impact of retroreflective chevron markings in combination with lighting configurations, as well as the measurement of “moth-to-flame” effects of emergency lighting on drivers was also investigated. The results indicate that higher intensity lights were judged consistently as more glaring, but were only rated as marginally more visible. This finding may suggest that dimming emergency lights at night could results in near equal visibility, but with significantly less glare. The rated visibility of the lights appears to be related to the perceived saturation of the color, while discomfort glare is related to the amount of short-wavelength spectral content. This suggest colors at the extreme ends of the light spectrum (red and blue) are more visible. However, the results indicate that blue lights, with their shorter wavelength are more glaring than red lights. Therefore, red may be a better choice for emergency vehicle lighting at night. The results also suggest that the presence of very highly reflective markings may decrease drivers’ ability to see first responders working adjacent to their vehicles. This is likely because the retro-reflective sheeting is compounding the emergency lighting visible to the drivers as well as the reflection of the driver’s headlights against the sheeting. Taking the study in its totality, it is likely that national standards are needed which specify the maximum intensities for emergency vehicle lighting at night. Further research is needed to identify these levels and likewise investigate the maximum luminance for retro-reflective sheeting