Seeing Pedestrians at Night: The Benefits of Biological Motion are Robust to Clutter

Collisions between vehicles and pedestrians are more common at night and insufficient conspicuity has been implicated as a causal factor. Incorporating the phenomenon of biological motion - placing reflective markers on a pedestrians' major joints has been shown to make pedestrians more conspicuous to drivers at night. However, most on-road tests have been conducted in scenarios relatively free of visual clutter. We tested whether the presence of extraneous points of light degrades drivers' ability to detect pedestrians wearing reflectors in several different configurations. Twelve younger (21–34 years) and 12 older (61–78 years) volunteers drove an instrumented vehicle 12 laps around a 1.8 km closed-road circuit at night and pressed a button whenever they realized that a pedestrian was present. Two pedestrians were positioned on the road's shoulder wearing either all black clothing or all black clothing with 663 cm2 of silver retroreflective markings in four different configurations. One pedestrian walked in place at a point that was, on half of the laps, surrounded by reflective cones and posts (clutter). To test the effects of pedestrian motion, the other pedestrian stood still during half the laps and walked in place during the other half and was always surrounded by clutter. Reflector configuration dramatically influenced conspicuity. Without reflective markers, or with a reflective vest, most pedestrians were never detected. When pedestrians wore reflectors on their ankles and wrists, however, younger and older drivers responded at a mean distance of 285 m and 141 m, respectively. Importantly, the presence of visual clutter did not significantly influence response distances (p.05). Pedestrian motion enhanced conspicuity, particularly for older drivers. These results confirm that the phenomenon of biological motion can dramatically enhance the nighttime conspicuity of pedestrians and indicate that this effect is robust to the presence of visual clutter.