Investigating Maximum Intensities for Yellow Rapid-Flashing Beacons at Night

Research has shown that rapid-flashing beacons (RFBs) at marked pedestrian crossings increase driver yielding rates at these locations. There are recommended minimum intensity levels for these devices, but no guidelines exist for maximum intensity levels that would cause light glare to drivers at night. This paper searches for evidence of such maximum thresholds by analyzing two data sets. One data set represented driver yielding at various RFB intensity levels; the data were collected from four cities in Arizona, Wisconsin, and Texas. The other data set was from a human factors study conducted on a closed course. These data were collected from volunteers in Texas who were asked to indicate their discomfort glare rating of various beacon intensities at a simulated pedestrian crossing. On the basis of the data set containing driver yielding rates, researchers estimated a minimum nighttime intensity of 1,100 candela (cd) was needed for the expected yielding rate at night to be at least the same as the yielding rate during the day. The wide dispersion of yielding rates in this data set made it impractical to find a minimum intensity in a more general way. More research is needed to reach a better explanation of the wide range of yielding rates. On the basis of the second data set, it was determined that driver discomfort from glare may become an issue at an intensity of approximately 1,000 cd. It is estimated that a maximum intensity of 1,350 cd at night should keep drivers' ratings of glare as being “unbearable” to 15% at most.