New Study of Driver Perception of Emergency Warning Lights and Retroreflective Markings Commissioned by The Emergency Responder Safety Institute Yields Surprising Findings

Are Higher Intensity and Greater Reflectivity Better?

A new research study from Emergency Responder Safety Institute (ERSI), “Effects of Emergency Vehicle Lighting Characteristics on Driver Perception and Behavior: Study Report,” investigated the impact of lighting color, intensity, modulation, and flash rate on driver behavior while approaching and passing a traffic incident scene at night. The impact of retroreflective chevron markings in combination with emergency lighting configurations, as well as the measurement of “moth-to-flame” effects of emergency lighting on drivers was also investigated. The research was conducted by Dr. John D. Bullogh (formerly with Rensselaer Polytechnic Institute and currently with the Light and Health Research Center in the Icahn School of Medicine at Mount Sinai) and Dr. Scott Parr of Embry-Riddle Aeronautical University in partnership with ERSI.

The full Study Report is available for download. It’s important reading for emergency responders, leaders, standards development organizations, and policy makers. The experiment design and findings are summarized here.

Under different emergency lighting setups volunteer civilians drove a closed course traffic incident scene at night consisting of a simulated fire apparatus in center-block position with a cone taper. Two SAE-compliant, commercially available blue, white, yellow, and red lights were mounted vertically on two tripods spaced apart at a distance approximating the left and right edge of the rear of a fire truck. A silhouette cutout of a firefighter wearing a high visibility safety vest was positioned adjacent to the lights. For some of the tests, researchers placed a panel of retroreflective red/yellow chevrons constructed with ASTM Type V sheeting materials directly behind each flashing light tripod. The researchers tested 14 combinations of lamp color, lamp intensity, pattern, flash rate, and presence of reflective markings next to the lights. Researchers measured vehicle distance to the lights and the distance at which drivers could distinguish the silhouette of a firefighter. They also administered a survey after the driver completed the course. Twenty drivers completed the testing.

The findings will surprise many emergency response professionals.

None of the variables tested had a significant effect on ratings of overall visibility of the road scene. But some individual factors and combined factors yielded findings of interest warranting further research.

Intensity

Study participants consistently judged higher intensity lights as more glaring but only marginally more visible than lights of lower intensity. Lower intensity lights remained highly visible. Using lower intensities at night will reduce discomfort glare without reducing the lights’ visibility. This finding indicates that stationary vehicles in nighttime blocking mode should be sufficiently visible with lower intensity lights.

Color

Drivers’ rated visibility of lights appeared to be related to the perceived saturation of their color. Blue and red lights have the greatest perceived saturation and were judged to be brighter than white and yellow lights of the same intensity. Blue and white lights were rated as most glaring. Yellow and red lights were least glaring. This data suggests that red lights for stationary blocking operations may offer the best combination of better visibility with less glare.

“Moth to Flame”

None of the variables tested caused drivers to move their vehicles either toward or away from the lights. Therefore, the data in this test did not support or disprove the “moth to flame” effect.

High Visibility Markings

When fluorescent and reflective markings were present, drivers did not see the firefighter silhouette until they were closer to it. This was the most unexpected finding of the study. Of the four setups tested, high intensity lights with no markings produced the longest detection distance, meaning drivers could see the firefighter silhouette from the furthest away. High intensity lights combined with high visibility markings yielded the shortest detection distance. Reflective markings may increase the amount of scattered light entering the eyes of a driver, thereby making the responder less visible. This study raises the possibility that combining high intensity lights with high visibility markings may make it more difficult for drivers to see responders on foot at night, even when the responders wear high visibility vests. Further research is planned to determine if lower grade retroreflective markings will help improve the conspicuity of emergency personnel operating near emergency vehicles and traffic.

More research is needed to further describe and understand these findings as well as new questions they raise. To stay informed on research into emergency lighting, visit the Emergency Vehicles page on ResponderSafety.com. This page also includes links to additional resources on emergency lighting and emergency vehicles.

This study was produced under a contract between the U.S. Fire Administration and the Cumberland Valley Volunteer Firemen’s Association’s Emergency Responder Safety Institute, which subcontracted with the Lighting Research Center at Rensselaer Polytechnic Institute and Embry-Riddle Aeronautical University to perform the research. Additional funding was provided by the Embry-Riddle Aeronautical University Office of Undergraduate Research and the Dwight D. Eisenhower Transportation Fellowship Program within the U.S. Department of Transportation.