Effects of Warning Lamps on Pedestrian Visibility and Driver Behavior

iii EXECUTIVE SUMMARY This report describes a field study that was performed to provide better information about how warning lamps for emergency vehicles affect the vision and driving performance of surrounding drivers, with special emphasis on understanding any ways in which those lamps might have negative effects on safety. The situations of most concern for this study are those in which an emergency professional is standing or working near a parked emergency vehicle and is therefore at risk of being struck by passing traffic. In such situations, warning lamps on the emergency vehicle can cause glare for the drivers of passing vehicles, possibly reducing their ability to see and avoid collisions with pedestrians near the emergency vehicle. The present study was designed to address questions in three primary areas: 1. Nighttime glare from warning lamps. How do warning lamp characteristics such as intensity, color, and flash pattern affect the tendency for the lamps to reduce the visibility of pedestrians in an emergency scene? How are those effects influenced by the degree of retroreflective marking of the pedestrian? 2. Effects on driving performance. How do the visual characteristics of warning lamps and of pedestrians affect drivers' behavior, including lateral position, while passing a parked emergency vehicle? Do drivers tend to deviate toward or away from warning lamps based on their photometric characteristics? 3. Nighttime photometry. What are the implications of differences in spectral sensitivity between day and night vision for measuring the light output of emergency lamps in a way that will best describe their effects—both intended and unintended—on drivers of other vehicles? When and how is it appropriate to measure light using photometric units designed for daytime light levels (photopic units) versus those designed for nighttime light levels (scotopic units)? The study was conducted on a closed-course test track. Participants selected from the driving population were asked to drive on the track at night, while attempting to detect pedestrian mannequins that were positioned near a parked vehicle displaying experimental warning lamps. The warning lamps used LED sources and were varied in color (blue, red), flash pattern (steady, flashing in phase, flashing out of phase), and intensity (low, high). Blue and red were chosen because they are the colors that maximize the differences that can be expected between the color sensitivity of human vision when it is adapted to daytime versus nighttime light levels. The iv pedestrian mannequins were varied in …